Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2016	Feb. 15, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	FY
Trading Symbol	MACK
Entity Registrant Name	MERRIMACK PHARMACEUTICALS INC
Entity Central Index Key	0001274792
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		130,570,161
Entity Public Float			$ 657,498,088

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 21,524	$ 185,606
Restricted cash	102	101
Accounts receivable, net	17,469	6,483
Inventory	14,554	3,717
Prepaid expenses and other current assets	3,786	5,487
Total current assets	57,435	201,394
Restricted cash	674	584
Property and equipment, net	15,765	21,915
Other assets	27	27
Intangible assets, net	3,977	7,355
Goodwill	3,605	3,605
Total assets	81,483	234,880
Current liabilities:
Accounts payable, accrued expenses and other	49,982	52,082
Deferred revenues	36,226	50,137
Deferred rent	2,014	1,527
Total current liabilities	88,222	103,746
Deferred revenues, net of current portion	25,673	51,197
Deferred rent, net of current portion	3,386	4,926
Deferred tax incentives, net of current portion		1,045
Long-term debt, net of current portion	216,861	257,655
Total liabilities	334,142	418,569
Commitments and contingencies
Non-controlling interest	(1,539)	239
Stockholders’ deficit:
Preferred stock, $0.01 par value: 10,000 shares authorized at December 31, 2016 and 2015; no shares issued or outstanding at December 31, 2016 or 2015
Common stock, $0.01 par value: 200,000 shares authorized at December 31, 2016 and 2015, 130,197 and 115,871 issued and outstanding at December 31, 2016 and 2015, respectively	1,302	1,159
Additional paid-in capital	702,377	617,145
Accumulated deficit	(954,799)	(802,232)
Total stockholders’ deficit	(251,120)	(183,928)
Total liabilities, non-controlling interest and stockholders’ deficit	$ 81,483	$ 234,880

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	130,197,000	115,871,000
Common stock, shares outstanding	130,197,000	115,871,000

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Product revenues, net	$ 53,064	$ 4,328
License and collaboration revenues	87,119	84,930	$ 102,756
Other revenues	4,090
Total revenues	144,273	89,258	102,756
Costs and expenses:
Cost of revenues	6,912	46
Research and development expenses	160,917	160,988	138,495
Selling, general and administrative expenses	80,729	57,795	30,517
Restructuring expenses	5,856
Total costs and expenses	254,414	218,829	169,012
Loss from operations	(110,141)	(129,571)	(66,256)
Other income and expenses:
Interest income	276	99	114
Interest expense	(43,645)	(19,232)	(18,230)
Other (expense) income, net	(8)	917	813
Net loss	(153,518)	(147,787)	(83,559)
Net (loss) income attributable to non-controlling interest	(1,778)	170	(268)
Net loss attributable to Merrimack Pharmaceuticals, Inc.	(151,740)	(147,957)	(83,291)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities		74	(50)
Other comprehensive income (loss)		74	(50)
Comprehensive loss	$ (151,740)	$ (147,883)	$ (83,341)
Net loss per share available to common stockholders—basic and diluted	$ (1.21)	$ (1.33)	$ (0.80)
Weighted-average common shares used in computing net loss per share available to common stockholders—basic and diluted	125,334	111,356	104,410

Consolidated Statements of Non-Controlling Interest and Stockholders' Deficit - USD ($) shares in Thousands, $ in Thousands	Total	Silver Creek Series B Preferred Stock [Member]	Silver Creek Series C Preferred Stock [Member]	Convertible Notes [Member]	Silver Creek [Member]	Silver Creek [Member] Silver Creek Series B Preferred Stock [Member]	Silver Creek [Member] Silver Creek Series C Preferred Stock [Member]	Non-Controlling Interest [Member]	Non-Controlling Interest [Member] Silver Creek Series B Preferred Stock [Member]	Non-Controlling Interest [Member] Silver Creek Series C Preferred Stock [Member]	Non-Controlling Interest [Member] Silver Creek [Member]	Common Stock [Member]	Common Stock [Member] Convertible Notes [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Silver Creek Series B Preferred Stock [Member]	Additional Paid-In Capital [Member] Silver Creek Series C Preferred Stock [Member]	Additional Paid-In Capital [Member] Convertible Notes [Member]	Additional Paid-In Capital [Member] Silver Creek [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2013	$ (43,465)							$ 337				$ 1,025		$ 527,779					$ (24)	$ (572,245)
Balance (in shares) at Dec. 31, 2013												102,523
Exercise of stock options and common stock warrants	10,425											$ 42		10,383
Exercise of stock options and common stock warrants (shares)												4,174
Issuance of stock due to conversion of convertible notes					$ 678						$ 366							$ 678
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.					$ 400
Stock-based compensation	13,197													13,197
Other comprehensive income (loss)	(50)																		(50)
Loss attributable to non-controlling interest	634							(634)												634
Net loss	(83,559)																			(83,559)
Balance at Dec. 31, 2014	(102,140)							69				$ 1,067		552,037					(74)	(655,170)
Balance (in shares) at Dec. 31, 2014												106,697
Exercise of stock options and common stock warrants	10,101											$ 54		10,047
Exercise of stock options and common stock warrants (shares)												5,360
Issuance of common stock in at the market offering, net of issuance costs	38,560											$ 38		38,522
Issuance of common stock in at the market offering, net of issuance costs (shares)												3,814
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.		$ 1,188				$ 900			$ 895						$ 1,188
Stock-based compensation	15,351													15,351
Other comprehensive income (loss)	74																		$ 74
Loss attributable to non-controlling interest	725							(725)												725
Net loss	(147,787)																			(147,787)
Balance at Dec. 31, 2015	(183,928)							239				$ 1,159		617,145						(802,232)
Balance (in shares) at Dec. 31, 2015												115,871
Exercise of stock options	$ 6,442											$ 20		6,422
Exercise of stock options (shares)	1,958											1,958
Issuance of stock due to conversion of convertible notes				$ 100,961									$ 123				$ 100,838
Issuance of stock due to conversion of convertible notes (shares)													12,368
Consideration allocated to reacquisition of conversion feature of convertible notes due 2020	$ (39,923)													(39,923)
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.			$ 2,689				$ (800)			$ (827)						$ 2,689
Stock-based compensation	15,206													15,206
Loss attributable to non-controlling interest	951							(951)												951
Net loss	(153,518)																			(153,518)
Balance at Dec. 31, 2016	$ (251,120)							$ (1,539)				$ 1,302		$ 702,377						$ (954,799)
Balance (in shares) at Dec. 31, 2016												130,197

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net loss	$ (153,518)	$ (147,787)	$ (83,559)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense	6,004	8,217	8,511
Non-cash loss on extinguishment of convertible notes due 2020	14,566
Loss on disposal of property and equipment	493	4
Gain on sale of property and equipment	(40)
Impairment of in-process research and development intangible asset	2,800
Depreciation and amortization expense	6,249	4,288	3,223
Stock-based compensation expense	14,865	15,351	13,197
Purchased premiums and interest on marketable securities			858
Changes in operating assets and liabilities:
Accounts receivable	(10,986)	(3,170)	2,587
Prepaid expenses and other current assets	1,910	(850)	827
Inventory	(9,688)	(3,717)
Accounts payable, accrued expenses and other	(3,869)	13,557	(646)
Deferred revenues	(39,435)	6,377	19,482
Deferred rent and tax incentives	408	2,374	712
Net cash used in operating activities	(170,241)	(105,356)	(34,808)
Cash flows from investing activities
Purchase of marketable securities	(84,262)		(111,832)
Proceeds from sales and maturities of marketable securities	84,160	87,899	111,858
Purchase of property and equipment	(3,155)	(12,789)	(6,035)
Other investing activities, net			(2)
Net cash (used in) provided by investing activities	(3,257)	75,110	(6,011)
Cash flows from financing activities
Proceeds from exercise of options and warrants to purchase common stock	6,224	10,087	10,384
Proceeds from issuance of convertible promissory notes by Silver Creek Pharmaceuticals, Inc.			1,044
Proceeds from at the market offering, net of issuance costs		38,560
Proceeds from issuance of senior secured notes due 2022, net of issuance costs		169,434
Proceeds from issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.	3,361	2,083
Repayment of loans payable to Hercules Technology Growth Capital, Inc.		(40,000)
Other financing activities, net	(169)		(7)
Net cash provided by financing activities	9,416	180,164	11,421
Net (decrease) increase in cash and cash equivalents	(164,082)	149,918	(29,398)
Cash and cash equivalents, beginning of period	185,606	35,688	65,086
Cash and cash equivalents, end of period	21,524	185,606	35,688
Non-cash investing and financing activities
Purchases of property and equipment in accounts payable, accrued expenses and other	130	816	704
Receivables related to stock option exercises in prepaid expenses and other current assets	232	14
Receivables related to the sale of property and equipment in prepaid expenses and other current assets	40
Principal amount of convertible notes	64,209
Supplemental disclosure of cash flows
Cash paid for interest	23,914	10,087	9,510
Silver Creek [Member]
Cash flows from financing activities
Cash and cash equivalents, beginning of period	700
Cash and cash equivalents, end of period	$ 1,900	$ 700
Silver Creek [Member] \| Series A Preferred Stock [Member]
Non-cash investing and financing activities
Principal amount of convertible notes			$ 1,044

Nature of the Business and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Nature of the Business and Summary of Significant Accounting Policies

1. Nature of the Business and Summary of Significant Accounting Policies

Nature of the Business

Merrimack Pharmaceuticals, Inc. (the “Company”) is a biopharmaceutical company discovering, developing and commercializing innovative medicines consisting of novel therapeutics paired with diagnostics for the treatment of cancer. The Company has one marketed therapeutic oncology product and multiple targeted therapeutic oncology candidates in clinical development. The Company’s most advanced program is its therapeutic ONIVYDE^®, which it markets in the United States. In addition to ONIVYDE and its product candidates in clinical development, the Company has multiple product candidates in preclinical development. The Company has tailored ONIVYDE and its other product candidates to target specific disease mechanisms that its research suggests are common across many solid tumor types. The Company believes that ONIVYDE and its other product candidates have the potential to address major unmet medical needs. The Company also has an agreement to utilize its manufacturing expertise to develop, manufacture and exclusively supply bulk drug product to a third party, who will in turn process the drug into finished product and commercialize it globally following regulatory approval. The Company was incorporated in the Commonwealth of Massachusetts in 1993 and reincorporated in the State of Delaware in October 2010.

The Company is subject to risks and uncertainties common to companies in the biopharmaceutical industry, including, among other things, its ability to secure additional capital to fund operations, success of clinical trials, development by competitors of new technological innovations, dependence on collaborative arrangements, protection of proprietary technology, compliance with government regulations and dependence on key personnel. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, infrastructure and extensive compliance reporting capabilities.

The Company has incurred significant expenses and operating losses to date, and it expects to continue to incur significant expenses and operating losses for at least the next several years. The accompanying consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. The Company performed an evaluation of its ability to continue as a going concern within one year after the date that the consolidated financial statements are issued, as described more fully in Note 22, “Going Concern.”

The Company may seek additional funding through public or private debt or equity financings, through existing or new collaboration arrangements, or through divestitures of its assets. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into additional collaborative arrangements or divest its assets. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Arrangements with collaborators or others may require the Company to relinquish rights to certain of its technologies or product candidates. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate its research and development programs or commercialization efforts, which could adversely affect its business prospects.

On January 7, 2017, the Company entered into an Asset Purchase and Sale Agreement (the “Asset Sale Agreement”) with Ipsen S.A. (“Ipsen”). Pursuant to the Asset Sale Agreement, Ipsen will acquire the Company’s right, title and interest in the non-cash assets, equipment, inventory, contracts and intellectual property primarily related to or used in the Company’s business operations and activities involving or relating to developing, manufacturing and commercializing ONIVYDE and MM-436 (the “Commercial Business”). This transaction is described more fully in Note 23, “Subsequent Events.”

Summary of Significant Accounting Policies

Segment Information

Operating segments are defined as components of an enterprise engaging in business activities for which discrete financial information is available and regularly reviewed by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business as one operating segment and the Company operates in only one geographic region.

Basis of Presentation and Consolidation

The accompanying consolidated financial statements have been prepared under U.S. generally accepted accounting principles (“GAAP”) and include the accounts of the Company and its wholly owned subsidiary, Merrimack Pharmaceuticals (Bermuda) Ltd., which was merged with and into the Company during the third quarter of 2014. The Company also consolidates its majority owned subsidiary, Silver Creek Pharmaceuticals, Inc. (“Silver Creek”). All intercompany transactions and balances have been eliminated in consolidation.

Use of Estimates

GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues, expenses and related disclosures. The Company bases estimates and judgments on historical experience and on various other factors that it believes to be reasonable under the circumstances. The most significant estimates in these consolidated financial statements include, but may not be limited to, revenue recognition, including the estimated percentage of billable expenses in any particular budget period, periods of meaningful use of licensed products, estimated service periods and services to be completed under a collaboration, estimates used in accounting for revenue separability and recognition, estimates of discounts and allowances related to commercial sales of ONIVYDE, estimates utilized in the valuation of inventory, useful lives with respect to long-lived assets and intangible assets, accounting for stock-based compensation, contingencies, intangible assets, goodwill, in-process research and development (“IPR&D”), tax valuation reserves and accrued expenses. The Company’s actual results may differ from these estimates under different assumptions or conditions. The Company evaluates its estimates on an ongoing basis. Changes in estimates are reflected in reported results in the period in which they become known by the Company’s management.

Cash, Cash Equivalents and Restricted Cash

Cash and cash equivalents are short-term, highly liquid investments with original maturities of three months or less at the date of purchase. Investments qualifying as cash equivalents primarily consist of money market funds, commercial paper, corporate notes and bonds and certificates of deposit.

Cash accounts with any type of restriction are classified as restricted cash. If restrictions are expected to be lifted in the next twelve months, the restricted cash account is classified as current. As of December 31, 2016 and 2015, the Company recorded restricted cash of $0.8 million and $0.7 million, respectively, which was primarily related to the Company’s facility lease.

Marketable Securities

The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available-for-sale. Available-for-sale securities may consist of U.S. government agencies securities, commercial paper, corporate notes and bonds and certificates of deposit, which are maintained by an investment manager. Available-for-sale securities are carried at fair value, with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ deficit until realized. To determine whether an other-than-temporary impairment exists, the Company performs an analysis to assess whether it intends to sell, or whether it would more likely than not be required to sell, the security before the expected recovery of the amortized cost basis. Where the Company intends to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary and the full amount of the unrealized loss is recognized on the statement of operations and comprehensive loss as an other-than-temporary impairment charge. When this is not the case, the Company performs additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where the Company does not expect to receive cash flows, based on using a single best estimate, sufficient to recover the amortized cost basis of a security and amount of the loss recognized in other income (expense). Realized gains and losses are recognized in interest income. Any premium or discount arising at purchase is amortized and/or accreted to interest income.

Inventory

The Company values its inventories at the lower of cost or net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials and manufacturing overhead, on a first-in, first-out basis. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded as a component of “Cost of revenues.”

The Company capitalizes inventory costs associated with the Company’s products after regulatory approval when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized. Inventory acquired prior to receipt of marketing approval of a product candidate is expensed as research and development expense as incurred. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign.

Shipping and handling costs for product shipments are recorded as incurred as a component of “Cost of revenues” along with amortization expense related to definite-lived intangible assets, costs associated with manufacturing the product and any inventory reserves or write-downs.

Property and Equipment

Property and equipment, including leasehold improvements, are recorded at cost and depreciated when placed into service using the straight-line method, based on their estimated useful lives as follows:

Asset Classification		Estimated Useful Life (in years)
Lab equipment		3 - 7
IT equipment		3 - 7
Leaseholds improvements		Lesser of useful life or lease term
Furniture and fixtures		3 - 7

Costs for capital assets not yet placed into service have been capitalized as construction-in-progress and will be depreciated in accordance with the above guidelines once placed into service. Costs for repairs and maintenance are expensed as incurred, while major betterments are capitalized. The Company capitalizes interest cost incurred on funds used to construct property and equipment. The capitalized interest is recorded as part of the asset to which it relates and is depreciated over the asset’s estimated useful life. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is reflected in earnings.

The Company reviews its long-lived assets for impairment whenever events or changes in business circumstances indicate that the carrying amount of assets may not be fully recoverable or that the useful lives of these assets are no longer appropriate. Each impairment test is based on a comparison of the undiscounted cash flow to the recorded value of the asset. If impairment is indicated, the asset will be written down to its estimated fair value on a discounted cash flow basis.

Goodwill and Intangible Assets

Goodwill and indefinite-lived intangible assets, including IPR&D assets, are evaluated for impairment on an annual basis or more frequently if an indicator of impairment is present. The Company performs its annual goodwill and IPR&D impairment evaluations on August 31^st.

When performing an evaluation of goodwill impairment, the Company has the option to first assess qualitative factors to determine whether it is necessary to perform the quantitative two-step impairment test. If the Company elects this option and finds, as a result of the qualitative assessment, that it is more likely than not that the fair value of the reporting unit is less than its carrying amount, the quantitative two-step impairment test is required; otherwise, further testing is not required. This requires the Company to assess the impact of significant events, milestones and changes to expectations and activities that may have occurred since the last impairment evaluation. Significant changes to these estimates, judgments and assumptions could materially change the outcome of the impairment assessment. Alternatively, the Company may elect to not first assess qualitative factors and immediately perform the quantitative two-step impairment test. If such an election occurs, in the first step, the fair value of the Company’s reporting unit is compared to the carrying value. If the carrying value of the net assets assigned to the reporting unit exceeds the fair value of the reporting unit, then the second step of the impairment test is performed in order to determine the implied fair value of the reporting unit’s goodwill. If the carrying value of the reporting unit’s goodwill exceeds the implied fair value, then the Company would record an impairment loss equal to the difference. As described above, the Company operates in one operating segment, which is considered the only reporting unit.

The Company commences amortization of indefinite-lived intangible assets, such as IPR&D, once the associated research and development efforts have been completed. The Company amortizes these product-related intangible assets over their estimated useful lives, and amortization expense is recorded as a component of “Cost of revenues.” The Company amortizes other definite-lived assets, such as core technology, over their estimated useful lives as a component of “Research and development expenses.” Definite-lived intangible assets are evaluated for impairment whenever events or circumstances indicate that the carrying value may not be fully recoverable.

Accrued Expenses

As part of the process of preparing financial statements, the Company is required to estimate accrued expenses. This process involves identifying services that have been performed on the Company’s behalf and estimating the level of services performed and the associated costs incurred for such services where the Company has not yet been invoiced or otherwise notified of actual cost. The Company records these estimates in its consolidated financial statements as of each balance sheet date. Examples of estimated accrued expenses include:

•

fees due to contract research organizations in connection with preclinical and toxicology studies and clinical trials;

•

fees paid to investigative sites in connection with clinical trials; and

•

professional service fees.

In accruing service fees, the Company estimates the time period over which services will be provided and the level of effort in each period. If the actual timing of the provision of services or the level of effort varies from the estimate, the Company adjusts the accrual accordingly. In the event that the Company does not identify costs that have been incurred or it under or overestimates the level of services performed or the costs of such services, its actual expenses could differ from such estimates. The date on which some services commence, the level of services performed on or before a given date and the cost of such services are often subjective determinations. The Company prepares its estimates based on the facts and circumstances known to it at the time and in accordance with GAAP. There have been no material changes in estimates for the periods presented.

Non-Controlling Interest

Non-controlling interest represents the non-controlling stockholders’ proportionate share of preferred stock and net loss of the Company’s majority owned consolidated subsidiary, Silver Creek. The non-controlling stockholders’ proportionate share of the preferred stock in Silver Creek is reflected as non-controlling interest in the Company’s consolidated balance sheets as a component of mezzanine equity.

Revenue Recognition

The Company recognizes revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; delivery has occurred or services have been rendered; the price to the customer is fixed or determinable; and collectability is reasonably assured.

Product Revenues, Net

The Company sells ONIVYDE to a limited number of specialty pharmaceutical distributors in the United States (collectively, its “Distributors”). The Company’s Distributors subsequently resell the products to healthcare providers. The Company recognizes revenue on product sales when title and risk of loss have passed to the Distributor, which is typically upon delivery. Product revenues are recorded net of applicable reserves for discounts and allowances.

In order to conclude that the price is fixed or determinable, the Company must be able to reasonably estimate its net product revenues upon delivery to its Distributors. As such, the Company estimates its net product revenues by deducting from its gross product revenues trade allowances, estimated contractual discounts, estimated Medicaid rebates, estimated reserves for product returns and estimated costs of other incentives offered to patients.

These discounts and allowances are based on estimates of the amounts earned or to be claimed on the related sales. The Company’s estimates take into consideration its historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted Distributor buying and payment patterns. Actual amounts may ultimately differ from the Company’s estimates. If actual results vary, the Company will adjust these estimates, which could have an effect on earnings in the period of adjustment.

Product revenue reserves and allowances that reduce gross revenue are categorized as follows:

Trade Allowances: The Company pays fees to its Distributors for providing certain data to the Company as well as for maintaining contractual inventory and service levels. These trade allowances are recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized.

Rebates and Chargeback Discounts: The Company is subject to discount obligations under state Medicaid programs and the Public Health Service 340B Drug Pricing Program, contracts with Federal government entities purchasing via the Federal Supply Schedule and various private organizations, such as group purchasing organizations (collectively, its “Third-party Payors”). The Company estimates the rebates and chargeback discounts it will provide to Third-party Payors, based upon its estimated payor mix, and deducts these estimated amounts from its gross product revenues at the time revenue is recognized. Chargeback discounts are processed when the Third-party Payor purchases the product at a discount from the Distributor, who then in turn charges back to the Company the difference between the price initially paid by the Distributor and the discounted price paid by the Third-party Payor. These chargeback discounts are recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized. Rebates that are invoiced directly to the Company are recorded as accrued liabilities on the consolidated balance sheet at the time revenue is recognized.

Product Returns: An allowance for product returns is established for returns expected to be made by Distributors and is recorded at the time revenue is recognized, resulting in a reduction to product sales. In accordance with contractual terms, Distributors have the right to return unopened and undamaged product that is within a permissible number of months before and after the product’s expiration date, subject to contractual limitations. The Company has the ability to monitor inventory levels and the shelf life of product at Distributors and can contractually control the amount of inventory that is sold to Distributors. Based on inventory levels held by Distributors and the structure of the Company’s distribution model, the Company has concluded that it has the ability to reasonably estimate product returns at the time revenue is recognized. The Company’s estimated rate of return is based on historical rates of return for comparable oncology products.

Other Incentives: The Company offers co-pay mitigation support to commercially insured patients. The Company’s co-pay mitigation program is intended to reduce each participating patient’s portion of the financial responsibility for a product’s purchase price to a specified dollar amount. Based upon the terms of the Company’s co-pay mitigation program, the Company estimates average co-pay mitigation amounts in order to establish a reserve for co-pay mitigation claims and deducts these estimated amounts from its gross product revenues at the later of the date that (i) the revenues are recognized or (ii) the incentive is offered. Claims under the Company’s co-pay mitigation program are subject to expiration.

License and Collaboration Revenues

The Company enters into biopharmaceutical product development agreements with collaborative partners for the research and development of therapeutic and diagnostic products. The terms of the agreements may include nonrefundable signing and licensing fees, funding for research, development and manufacturing, milestone payments and royalties or profit-sharing on any product sales derived from collaborations. These multiple-element arrangements are analyzed to determine whether the deliverables can be separated or whether they must be accounted for as a single unit of accounting.

The revenue recognition guidance related to multiple-element arrangements requires entities to separate and allocate consideration in a multiple-element arrangement according to the relative selling price of each deliverable. The fair value of deliverables under the arrangement may be derived using a best estimate of selling price if vendor specific objective evidence and third-party evidence are not available. Deliverables under the arrangement will be separate units of accounting provided that a delivered item has value to the customer on a stand-alone basis and if the arrangement does not include a general right of return relative to the delivered item and delivery or performance of the undelivered item is considered probable and substantially in the control of the vendor.

In September 2014, the Company entered into a license and collaboration agreement (the “Baxalta Agreement”) with Baxter International Inc., Baxter Healthcare Corporation and Baxter Healthcare SA (collectively, “Baxter”) for the development and commercialization of ONIVYDE outside of the United States and Taiwan (the “Licensed Territory”). In connection with Baxter International Inc.’s separation of the Baxalta business, the Baxalta Agreement was assigned to Baxalta Incorporated, Baxalta US Inc. and Baxalta GmbH (collectively, “Baxalta”) during the second quarter of 2015. The Baxalta Agreement was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements. The Company determined that the obligations under this agreement represent a single unit of accounting and that the agreement represents a services agreement. As a result, the Company has estimated the level of effort expected to be completed as a result of providing the identified deliverables and will recognize revenue related to the agreement based on proportional performance as effort is completed over the expected services period.

The Company also entered into a collaboration agreement with Watson Laboratories, Inc. (“Actavis”) in November 2013, which was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements. See Note 4, “License and Collaboration Agreements,” for additional information.

Whenever the Company determines that an arrangement should be accounted for as a single unit of accounting, it determines the period over which the performance obligations would be performed and revenue would be recognized. If the Company cannot reasonably estimate the timing and the level of effort to complete its performance obligations under the arrangement, then revenue under the arrangement is recognized on a straight-line basis over the period the Company expects to complete its performance obligations.

The Company’s collaboration agreements may include additional payments upon the achievement of performance-based milestones. As milestones are achieved, a portion of the milestone payment, equal to the percentage of the total time that the Company has performed the performance obligations to date divided by the total estimated time to complete the performance obligations, multiplied by the amount of the milestone payment, will be recognized as revenue upon achievement of such milestone. The remaining portion of the milestone will be recognized over the remaining performance period. Milestones that are tied to regulatory approvals are not considered probable of being achieved until such approval is received. Milestones tied to counterparty performance are not included in the Company’s revenue model until the performance conditions are met.

Other Revenues

The Company is a party to separate commercial supply agreements with Baxalta and PharmaEngine, Inc. (“PharmaEngine”) pursuant to which the Company supplies ONIVYDE to these entities. Revenue is recognized under these commercial supply arrangements when the counterparty takes delivery of the commercial supply product and when the other general revenue recognition criteria outlined above are met.

The Company is also eligible to receive royalty revenues on Baxalta’s net sales of ONIVYDE in the Licensed Territory. The Company recognizes royalty revenues in the period that the related sales occur.

Research and Development Expenses

Research and development expenses are charged to expense as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including personnel-related costs, stock-based compensation, facilities, research-related overhead, clinical trial costs, contracted services, research-related manufacturing, license fees and other external costs. The Company accounts for nonrefundable advance payments for goods and services that will be used in future research and development activities as expenses when the services have been performed or when the goods have been received rather than when the payment is made.

Selling, General and Administrative Expenses

Selling, general and administrative expenses are comprised of salaries and other related costs for personnel, including stock-based compensation expenses and benefits, in the Company’s commercial, legal, intellectual property, business development, finance, information technology, corporate communications, investor relations and human resources departments. Other selling, general and administrative expenses include costs to support commercial sales, employee training and development, board of directors costs, depreciation, insurance expenses, facility-related costs not otherwise included in research and development expenses, professional fees for legal services, including patent-related expenses, and accounting and information technology services.

In connection with the commercial launch of ONIVYDE on October 26, 2015, the Company began incurring advertising expenses. Advertising expenses are expensed as incurred as a component of selling, general and administrative expenses. For the years ended December 31, 2016 and 2015, advertising expenses totaled $4.5 million and $1.0 million, respectively.

Stock-Based Compensation Expense

The Company accounts for its stock-based compensation awards in accordance with Accounting Standards Codification (“ASC”) 718, Compensation – Stock Compensation. ASC 718 requires all share-based payments to employees, including grants of employee stock options, to be recognized in the consolidated statements of operations and comprehensive loss based on their grant date fair values. For stock options granted to employees and to members of the Company’s Board of Directors for their service on the Board of Directors, the Company estimates the grant date fair value of each option award using the Black-Scholes option pricing model. The use of the Black-Scholes option pricing model requires the Company to make assumptions with respect to the expected term of the option, the expected volatility of the Company’s common stock consistent with the expected term of the option, the risk-free interest rate consistent with the expected term of the option and the expected dividend yield of the Company’s common stock. Stock-based compensation expense related to employee stock options is measured using the fair value of the award at the grant date, net of estimated forfeitures, and is adjusted annually to reflect actual forfeitures. Stock-based compensation expense is then recognized on a straight-line basis over the vesting period, which is also the requisite service period.

The Company records stock options issued to non-employees at fair value, remeasures to reflect the current fair value at each reporting period and recognizes expense over the related service period. When applicable, these equity instruments are accounted for based on the fair value of the consideration received or the fair value of the equity instrument issued, whichever is more reliably measurable.

Comprehensive Loss

Comprehensive loss consists of net loss and unrealized gains and losses on available-for-sale marketable securities.

Other (Expense) Income, Net

The Company records income related to tax incentive awards, foreign currency gains and losses and other income or expense-related items as components of “Other (expense) income, net” within the consolidated statements of operations and comprehensive loss.

The Company has been awarded tax incentives by the Massachusetts Life Sciences Center (“MLSC”), an independent agency of the Commonwealth of Massachusetts. These tax incentives require that the Company achieve certain hiring targets. Failure to maintain the additional headcount in subsequent periods could require the Company to repay some or all of the incentives. The Company recognizes the benefit of these incentives on a straight-line basis over the five-year performance period of each award, beginning when the Company achieves the hiring goal target, with a cumulative catch-up recognized in the period that the hiring goal target is achieved. The Company received MLSC tax incentives in 2011, 2013, 2014 and 2015 totaling $3.8 million in the aggregate, allowing the Company to monetize approximately $3.4 million of state research and development tax credits. As a result of the October 2016 corporate restructuring described more fully in Note 13, “Restructuring Activities,” the Company determined that it would be required to repay a portion of the 2014 and 2015 tax incentives received from the MLSC in the aggregate amount of $1.3 million. Such amounts have been classified as current liabilities as of December 31, 2016.

The Company recognized $0.1 million, $0.7 million and $0.4 million in income related to these MLSC tax incentives during the years ended December 31, 2016, 2015 and 2014, respectively.

Income Taxes

The Company accounts for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted rates in effect for the year in which these temporary differences are expected to be recovered or settled. Valuation allowances are provided if based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions and other issues. Reserves are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filing is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. Potential interest and penalties associated with such uncertain tax positions are recorded as components of income tax expense. To date, the Company has not taken any uncertain tax positions or recorded any reserves, interest or penalties.

Concentration of Credit Risk

Financial instruments that subject the Company to credit risk consist primarily of cash, cash equivalents and marketable securities. The Company places its cash deposits in accredited financial institutions and, therefore, the Company’s management believes these funds are subject to minimal credit risk. The Company invests cash equivalents and marketable securities in money market funds, U.S. government agencies securities and various corporate debt securities. Credit risk in these securities is reduced as a result of the Company’s investment policy to limit the amount invested in any one issue or any single issuer and to only invest in high credit quality securities. The Company has no significant off-balance sheet concentrations of credit risk such as foreign currency exchange contracts, option contracts or other hedging arrangements. The Company also is subject to credit risk from its accounts receivable related to its product sales and collaborators. The Company evaluates the creditworthiness of each of its customers and has determined that all of its customers are creditworthy. To date, the Company has not experienced significant losses with respect to the collection of its accounts receivable.

Gross revenues from each of the Company’s customers who individually accounted for 10% or more of total gross revenues for the years ended December 31, 2016, 2015 and 2014 consisted of the following:

	Years Ended December 31,
	2016		2015		2014
Baxalta		60%		93%		10%
Sanofi		—		—		90%
AmerisourceBergen Corporation		15%	<10%			—
McKesson Corporation		16%	<10%			—

Gross accounts receivable related to each of the Company’s customers who individually accounted for 10% or more of total gross accounts receivable as of December 31, 2016 and 2015 consisted of the following:

	December 31,
	2016		2015
Baxalta		20%		29%
AmerisourceBergen Corporation		25%		29%
McKesson Corporation		32%		25%
Cardinal Health, Inc.		21%		16%

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers (Topic 606),” which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. This guidance was originally effective for interim and annual periods beginning after December 15, 2016 and allows for adoption using a full retrospective method, or a modified retrospective method. Early adoption was originally not permitted. Subsequent to the issuance of ASU 2014-09, the FASB also issued the following updates related to ASC 606, Revenue from Contracts with Customers:

•

In August 2015, the FASB issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date,” whereby the effective date for the new revenue standard was deferred by one year. As a result of ASU 2015-14, the new revenue standard is now effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017, and early adoption is now permitted for annual periods beginning after December 15, 2016, including interim periods within that annual period.

•

In March 2016, the FASB issued ASU 2016-08, “Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net),” to clarify the implementation guidance on principal versus agent considerations.

•

In April 2016, the FASB issued ASU 2016-10, “Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing,” to clarify the principle for determining whether a good or service is “separately identifiable” from other promises in the contract and to clarify the categorization of licenses of intellectual property.

•

In May 2016, the FASB issued ASU 2016-12, “Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Technical Expedients,” to clarify guidance on transition, determining collectibility, non-cash consideration and the presentation of sales and other similar taxes.

•

In December 2016, the FASB issued ASU 2016-20, “Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers,” that allows entities not to make qualitative disclosures about remaining performance obligations in certain cases, adds disclosure requirements for entities that elect certain optional exemptions and adds twelve additional technical corrections and improvements to the new revenue standard.

The Company is currently evaluating the potential impact that the adoption of this guidance and the related transition guidance may have on the consolidated financial statements, including the adoption method to be utilized.

In August 2014, the FASB issued ASU 2014-15, “Presentation of Financial Statements – Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern,” outlining management’s responsibility to perform interim and annual assessments of an entity’s ability to continue as a going concern within one year of the date the financial statements are issued and providing guidance on determining when and how to disclose going concern uncertainties in the financial statements. This guidance is effective for annual and interim reporting periods ending after December 15, 2016, and the Company adopted this guidance for the year ended December 31, 2016, as described more fully in Note 22, “Going Concern.”

In January 2016, the FASB issued ASU 2016-01, “Financial Statements – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Liabilities,” which contains a number of provisions related to the measurement, presentation and disclosure of financial instruments. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual periods. Early adoption of this guidance is not permitted with the exception of certain specific presentation requirements that are not currently applicable to the Company. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance.

In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842),” which supersedes all existing lease accounting guidance within ASC 840, Leases. The new standard requires that lease assets and lease liabilities be recognized by lessees for those leases previously classified as operating leases under ASC 840, with limited exceptions. This update also creates a new definition of a lease and provides guidance as to whether a contract is or contains a lease. This guidance will be effective for annual reporting periods beginning after December 15, 2018, including interim periods within those annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the consolidated financial statements.

In March 2016, the FASB issued ASU 2016-06, “Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments,” which clarifies the requirements for assessing whether contingent call or put options that can accelerate the repayment of principal on debt instruments are clearly and closely related to their debt hosts. This guidance will be effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods, and early adoption is permitted. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance.

In March 2016, the FASB issued ASU 2016-09, “Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” which simplifies several areas of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either liabilities or equity and classification of excess tax benefits on the statement of cash flows. This guidance also permits a new entity-wide accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur. This guidance will be effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods, and early adoption is permitted. An entity that elects early adoption must adopt all of the amendments in the same period. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the consolidated financial statements.

In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments,” which represents a new credit loss standard that will change the impairment model for most financial assets and certain other financial instruments. Specifically, this guidance will require entities to utilize a new “expected loss” model as it relates to trade and other receivables. In addition, entities will be required to recognize an allowance for estimated credit losses on available-for-sale debt securities, regardless of the length of time that a security has been in an unrealized loss position. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the consolidated financial statements.

In August 2016, the FASB issued ASU 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments,” which is intended to reduce diversity in practice in how entities present certain types of cash transactions in the statement of cash flows. This guidance also clarifies how the predominance principle should be applied when classifying cash receipts and cash payments that have attributes of more than one class of cash flows. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption is permitted. An entity that elects early adoption must adopt all of the amendments in the same period. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance.

In November 2016, the FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash,” which will require entities to show the change in the total of cash, cash equivalents, restricted cash and restricted cash equivalents within the statement of cash flows. As a result, entities will no longer separately present transfers between unrestricted cash and restricted cash. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption is permitted. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance.

In January 2017, the FASB issued ASU 2017-04, “Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” which will eliminate the requirement to calculate the implied fair value of goodwill, commonly referred to as “Step 2” in the current goodwill impairment test. An entity will still have the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. This guidance will be effective for annual and interim impairment tests performed in annual reporting periods beginning after December 15, 2020, and early adoption is permitted for annual or interim impairment tests performed after January 1, 2017. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the consolidated financial statements.

Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

Consolidated Subsidiaries	12 Months Ended
Consolidated Subsidiaries	Dec. 31, 2016
Text Block [Abstract]
Consolidated Subsidiaries	2. Consolidated Subsidiaries Silver Creek Pharmaceuticals, Inc. On August 20, 2010, the Company acquired a controlling interest in Silver Creek. The Company has concluded that Silver Creek is a variable interest entity and that the Company is the primary beneficiary. The Company has the ability to direct the activities of Silver Creek through its ownership percentage and through the board of director seats controlled by the Company and its de facto agents. As such, Silver Creek is consolidated by the Company. During the year ended December 31, 2014, Silver Creek issued convertible notes to various lenders in the aggregate principal amount of $1.0 million. As of December 31, 2014, these outstanding borrowings and related accrued interest converted into shares of Silver Creek Series A preferred stock at the Series A preferred stock value of $1.00 per share. As a result of changes to the ownership composition of Silver Creek as of December 31, 2014, the non-controlling interest in Silver Creek increased by approximately $0.4 million. During the year ended December 31, 2015, Silver Creek issued and sold a total of 1.6 million shares of Silver Creek Series B preferred stock at a price of $1.35 per share to investors and received net cash proceeds of $2.1 million, after deducting issuance costs. As a result of changes to the ownership composition of Silver Creek as of December 31, 2015, the non-controlling interest in Silver Creek increased by approximately $0.9 million. As described more fully in Note 12, “Borrowings,” Silver Creek issued $1.0 million of convertible promissory notes (the “Silver Creek Notes”) in May 2016. In August 2016, Silver Creek issued $0.2 million of additional Silver Creek Notes under the same terms as the May 2016 issuance. In December 2016, these outstanding borrowings and related accrued interest were converted into shares of Silver Creek Series C preferred stock at the Series C preferred stock value of $1.50 per share. In addition, Silver Creek sold 1.5 million additional shares of its Series C preferred stock to new investors at a price of $1.50 per share and received net cash proceeds of $2.1 million, after deducting issuance costs. In conjunction with this sale, Silver Creek also issued warrants to purchase 1.9 million shares of Silver Creek Series C preferred stock to the same new investors. As a result of changes to the ownership composition of Silver Creek as of December 31, 2016, the non-controlling interest in Silver Creek decreased by approximately $0.8 million. As of December 31, 2016 and 2015, the Company owned approximately 50% and 56% of the outstanding voting stock of Silver Creek, respectively, and recorded a non-controlling interest of approximately $(1.5) million and $0.2 million, respectively, as a component of mezzanine equity on the Company’s consolidated balance sheets based on the terms of the Silver Creek Series A, Series B and Series C preferred stock. As of December 31, 2016, the Company consolidated Silver Creek’s total assets and total liabilities of $2.0 million and $2.0 million, respectively. As of December 31, 2015, the Company consolidated Silver Creek’s total assets and total liabilities of $0.8 million and $0.2 million, respectively. As of December 31, 2016 and 2015, the Company’s unrestricted cash and cash equivalents balance included $1.9 million and $0.7 million, respectively, of cash and cash equivalents held by Silver Creek that is designated for the operations of Silver Creek. Merrimack Pharmaceuticals (Bermuda) Ltd. Merrimack Pharmaceuticals (Bermuda) Ltd. was incorporated in Bermuda during 2011 and merged with and into the Company during the third quarter of 2014.

Net Loss Per Common Share

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Net Loss Per Common Share

3. Net Loss Per Common Share

Basic net loss per share is calculated by dividing the net loss available to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing the net loss available to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, convertible preferred stock, stock options and warrants are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive.

As discussed in Note 12, “Borrowings,” in July 2013, the Company issued $125.0 million aggregate principal amount of 4.50% convertible notes due 2020 (the “Convertible Notes”) in an underwritten public offering. Following the repayment and satisfaction in full of the Company’s obligations to Hercules Technology Growth Capital, Inc. (“Hercules”) under its Loan and Security Agreement with Hercules (the “Loan Agreement”), which occurred in December 2015, upon any conversion of the Convertible Notes, the Convertible Notes may be settled, at the Company’s election, in cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock. For purposes of calculating the maximum dilutive impact, it is presumed that the conversion premium will be settled in common stock, inclusive of a contractual make-whole provision resulting from a fundamental change, and the resulting potential common shares included in diluted earnings per share if the effect is more dilutive. As of December 31, 2016, $60.8 million aggregate principal amount of the Convertible Notes remain outstanding.

The stock options, warrants and conversion premium on the Convertible Notes are excluded from the calculation of diluted loss per share because the net loss for the years ended December 31, 2016, 2015 and 2014 causes such securities to be anti-dilutive. Securities excluded from the calculation of diluted loss per share are shown in the chart below:

	Years Ended December 31,
(in thousands)	2016		2015		2014
Common stock warrants		—		—		2,381
Outstanding options to purchase common stock		19,025		19,211		19,567
Conversion of the Convertible Notes		12,158		25,000		25,000

License and Collaboration Agreements

12 Months Ended

Dec. 31, 2016

Organization Consolidation And Presentation Of Financial Statements [Abstract]

License and Collaboration Agreements

4. License and Collaboration Agreements

Baxalta

On September 23, 2014, the Company and Baxter entered into the Baxalta Agreement for the development and commercialization of ONIVYDE in the Licensed Territory. In connection with Baxter’s separation of the Baxalta business, the Baxalta Agreement was assigned to Baxalta during the second quarter of 2015. As part of the Baxalta Agreement, the Company granted Baxalta an exclusive, royalty-bearing right and license under the Company’s patent rights and know-how to develop and commercialize ONIVYDE in the Licensed Territory. Baxalta is responsible for using commercially reasonable efforts to develop, obtain regulatory approvals for and, following regulatory approval, commercialize ONIVYDE in the Licensed Territory. A joint steering committee comprised of an equal number of representatives from each of Baxalta and the Company is responsible for approving changes to the global development plan for ONIVYDE, including all budgets, and overseeing the parties’ development and commercialization activities with respect to ONIVYDE. Unless otherwise agreed, the Company will be responsible for conducting all clinical trials contemplated by the global development plan for ONIVYDE and manufacturing all clinical material needed for such trials. Baxalta also has the option to manufacture ONIVYDE, in which case the Company will perform a technology transfer of its manufacturing process to Baxalta.

Under the terms of the Baxalta Agreement, the Company received a $100.0 million nonrefundable upfront cash payment in September 2014. In addition, the Company is eligible to receive from Baxalta (i) up to an aggregate of $100.0 million upon the achievement of specified research and development milestones, of which the Company has received $62.5 million from Baxalta through December 31, 2016, (ii) up to an aggregate of $520.0 million upon the achievement of specified regulatory milestones, of which the Company has received $60.0 million from Baxalta through December 31, 2016, and (iii) up to an aggregate of $250.0 million upon the achievement of specified sales milestones. Under the terms of the Baxalta Agreement, the Company will bear up to the first $98.8 million of costs related to the development of ONIVYDE for pancreatic cancer patients who have not previously received gemcitabine-based therapy; however, the Company expects most of these costs to be offset by payments received upon the achievement of clinical trial-related milestones. The Company and Baxalta will share equally all other clinical trial costs contemplated by the global development plan. The Company is also entitled to tiered, escalating royalties ranging from sub-teen double digits to low twenties percentages of net sales of ONIVYDE in the Licensed Territory.

If not terminated earlier by either party, the Baxalta Agreement will expire upon expiration of all royalty and other payment obligations of Baxalta under the Baxalta Agreement. Either party may terminate the Baxalta Agreement in the event of an uncured material breach by the other party. Baxalta may also terminate the Baxalta Agreement on a product-by-product, country-by-country or sub-territory-by-sub-territory basis or in its entirety, for its convenience, upon 180 days’ prior written notice. In addition, the Company may terminate the Baxalta Agreement if Baxalta challenges or supports any challenge of the Company’s licensed patent rights.

At the inception of the collaboration, the Company identified the following deliverables as part of the Baxalta Agreement: (i) license to develop and commercialize ONIVYDE in Baxalta’s territories, (ii) discovery, research, development and manufacturing services required to complete ongoing clinical trials related to ONIVYDE, (iii) discovery, research, development and manufacturing services needed to complete future clinical trials in further indications related to ONIVYDE, (iv) the option to perform a technology transfer of the Company’s manufacturing process related to the production of ONIVYDE to Baxalta and (v) participation on the joint steering committee.

The Company concluded that none of the deliverables identified at the inception of the collaboration has standalone value from the other undelivered elements. As such, all deliverables represent a single unit of accounting.

The Company has determined that the collaboration represents a services agreement and as such has estimated the level of effort expected to be completed as a result of providing the identified deliverables. The Company will recognize revenue from the nonrefundable upfront payment, forecasted non-substantive milestone payments and estimated payments related to discovery, research, development and technology transfer services based on proportional performance as effort is completed over the expected services period, which is estimated to be substantially complete by June 30, 2022. The Company will periodically review and, if necessary, revise the estimated service period related to its collaboration with Baxalta. As of December 31, 2016, the Company has achieved $62.5 million of the $90.0 million of forecasted non-substantive milestones that are included in the Company’s proportional performance revenue recognition model and $60.0 million of the $530.0 million of substantive milestones that are included in the Baxalta Agreement.

Research, development and regulatory milestones that are considered substantive on the basis of the contingent nature of the milestone will be recognized as revenue in full in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. All sales milestones will be accounted for in the same manner as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.

From the inception of the Baxalta Agreement through December 31, 2016, the Company has achieved the following substantive and non-substantive milestones:

•

In July 2015, the European Medicines Agency (“EMA”) accepted for review a Marketing Authorization Application (“MAA”) filed by Baxalta for ONIVYDE. As a result of this acceptance, the Company recognized $20.0 million of license and collaboration revenue related to a substantive milestone payment owed from Baxalta.

•

In August 2015, the Company achieved a $15.0 million milestone related to the submission of the protocol for the Company’s Phase 2 clinical trial of ONIVYDE in front-line metastatic pancreatic cancer. This milestone is a non-substantive milestone, and revenue related to the achievement of this milestone will be recognized through the proportional performance revenue recognition model.

•

In October 2015, the Company achieved a $47.5 million milestone related to the enrollment of the first patient in a Phase 2 clinical trial of ONIVYDE in front-line pancreatic cancer. This milestone is a non-substantive milestone, and revenue related to the achievement of this milestone will be recognized through the proportional performance revenue recognition model.

•

In June 2016, the South Korean Ministry of Food and Drug Safety (the “MFDS”) accepted for review a new drug application filed by Baxalta for ONIVYDE. As a result of this acceptance, the Company recognized $10.0 million of license and collaboration revenue related to a substantive milestone payment owed from Baxalta.

•

In October 2016, the European Commission granted marketing authorization to Baxalta for ONIVYDE in combination with 5-FU and leucovorin for the treatment of adult patients with metastatic adenocarcinoma of the pancreas who have progressed following gemcitabine-based therapy. As a result of this approval and the first commercial sale of ONIVYDE made by Baxalta during the fourth quarter of 2016, the Company recognized $30.0 million of license and collaboration revenue related to a substantive milestone payment owed from Baxalta.

During the years ended December 31, 2016, 2015 and 2014, the Company recognized license and collaboration revenues based on the following components of the Baxalta Agreement:

	Years Ended December 31,
(in thousands)	2016		2015		2014
Proportional performance revenue recognition model	$	47,119	$	64,930	$	10,460
Substantive milestones		40,000		20,000		—
Total	$	87,119	$	84,930	$	10,460

During the year ended December 31, 2016, the Company also recognized royalty revenues of $0.2 million related to the Baxalta Agreement.

As of December 31, 2016 and 2015, the Company maintained the following assets and liabilities related to the Baxalta Agreement:

	December 31,
(in thousands)	2016		2015
Accounts receivable, billed	$	860	$	1,336
Accounts receivable, unbilled		581		626
Deferred revenues		56,779		97,365

Of the $56.8 million of deferred revenue related to the Baxalta Agreement as of December 31, 2016, $36.2 million is classified as current in the consolidated balance sheets based upon the Company’s estimate of revenue that will be recognized under the proportional performance revenue recognition model as a result of effort expected to be completed within the next twelve months.

In February 2016, the Company and Baxalta entered into a commercial supply agreement (the “Baxalta Supply Agreement”) pursuant to which the Company supplies ONIVYDE to Baxalta and, at Baxalta’s option, manages fill and finish activities conducted by a third-party contract manufacturer for Baxalta. The Company began supplying ONIVYDE under the Baxalta Supply Agreement during the second quarter of 2016 and recognized $3.6 million of revenue during the year ended December 31, 2016.

Sanofi

On September 30, 2009, the Company and Sanofi entered into a license and collaboration agreement (the “Sanofi Agreement”) for the development and commercialization of MM-121. The Sanofi Agreement became effective on November 10, 2009, and Sanofi paid the Company a nonrefundable, noncreditable upfront license fee of $60.0 million. On June 17, 2014, the Company and Sanofi agreed to terminate the Sanofi Agreement effective December 17, 2014. In connection with the agreement to terminate the Sanofi Agreement, among other things, Sanofi transferred ownership of the investigational new drug application for MM-121 back to the Company in July 2014, and the Company waived Sanofi’s obligation to reimburse the Company for MM-121 development costs incurred after the effective termination date. Following the termination of the Sanofi Agreement, the Company is not entitled to receive any additional fees, milestone payments or reimbursements from the collaboration.

The Company received total milestone payments of $25.0 million pursuant to the Sanofi Agreement. Under the Sanofi Agreement, Sanofi was responsible for all MM-121 development and manufacturing costs. Sanofi reimbursed the Company for direct costs incurred in both development and manufacturing and compensated the Company for its internal development efforts based on a full time equivalent rate.

The Company recognized cost reimbursements for MM-121 development services within the period they were incurred and billable. Billable expenses were identified during each specified budget period. In the event that total development services expense incurred and expected to be incurred during the same period exceeded the total contractually allowed billable amount for development services during that period, the Company recognized only a percentage of the development services incurred as revenue during that period.

At the inception of the collaboration, the Company determined that the license, the right to future technology, back-up compounds, participation on steering committees and manufacturing services performance obligations comprising the Sanofi Agreement represented a single unit of accounting. As the Company could not reasonably estimate its level of effort over the collaboration, the Company recognized revenue from the upfront payment, milestone payments and manufacturing services payments using the contingency-adjusted performance model over the expected development period, which was initially estimated at 12 years from the effective date of the Sanofi Agreement.

As a result of the Company and Sanofi agreeing to terminate the Sanofi Agreement, the development period was revised to end as of December 17, 2014. Accordingly, the balance of the deferred revenue remaining on April 1, 2014 was recognized prospectively on a straight-line basis over the remaining development period, ending on December 17, 2014, in accordance with current generally accepted principles on revenue recognition.

The Company recognized no revenue under the Sanofi agreement during the years ended December 31, 2016 or 2015. During the year ended December 31, 2014, the Company recognized revenue based on the following components of the Sanofi agreement:

(in thousands)	Year Ended December 31, 2014
Upfront payment	$	39,306
Milestone payment		16,377
Development services		18,904
Manufacturing services and other		17,709
Total	$	92,296

The Company performed development services for which revenue was recognized under the Sanofi Agreement in accordance with the specified budget period. During the year and specified budget periods ended December 31, 2013, the Company performed $10.1 million of development services in excess of recognized revenue. Of this amount, approximately $5.8 million was recognized as increased revenue in the year ended December 31, 2014 related to expenses incurred prior to December 31, 2013 upon the Company receiving budget approval for these overruns.

The Company maintained no assets or liabilities related to the Sanofi Agreement as of either December 31, 2016 or 2015.

PharmaEngine

On May 5, 2011, the Company and PharmaEngine entered into an assignment, sublicense and collaboration agreement (the “PharmaEngine Agreement”) under which the Company reacquired rights in Europe and certain countries in Asia to ONIVYDE. In exchange, the Company agreed to pay PharmaEngine a nonrefundable, noncreditable upfront payment of $10.0 million and up to an additional $80.0 million in aggregate development and regulatory milestones and $130.0 million in aggregate sales milestones. PharmaEngine is also entitled to tiered royalties on net sales of ONIVYDE in Europe and certain countries in Asia. PharmaEngine is not responsible for any future development costs of ONIVYDE except those required specifically for regulatory approval in Taiwan.

On September 22, 2014, the Company amended the PharmaEngine Agreement to redefine sublicense revenue and reduce the portion of sublicense revenue that the Company is required to pay to PharmaEngine. As a result of this amendment, the Company made a $7.0 million milestone payment to PharmaEngine in September 2014. Additionally, as a result of this amendment, a previously contingent $5.0 million milestone payment was paid to PharmaEngine in the second quarter of 2015. Prior to the amendment of the PharmaEngine Agreement, this milestone payment was contingent upon the award of certain specified regulatory designations. These milestone payments were recognized as research and development expense during the year ended December 31, 2014. In July 2015, the Company made an $11.0 million milestone payment to PharmaEngine in connection with the EMA’s acceptance for review of an MAA for ONIVYDE, which occurred, and was recognized as research and development expense, in the second quarter of 2015. In June 2016, the Company made a $10.0 million milestone payment to PharmaEngine in connection with the MFDS’s acceptance for review of a new drug application for ONIVYDE, which occurred, and was recognized as research and development expense, in the second quarter of 2016. In December 2016, the Company made a $25.5 million milestone payment to PharmaEngine in connection with Baxalta’s receipt of marketing authorization from the European Commission for ONIVYDE in combination with 5-FU and leucovorin for the treatment of adult patients with metastatic adenocarcinoma of the pancreas who have progressed following gemcitabine-based therapy, which occurred, and was recognized as research and development expense, in the fourth quarter of 2016.

During the years ended December 31, 2016, 2015 and 2014, the Company recognized research and development expenses of $35.6 million, $11.4 million and $12.6 million, respectively, related to the PharmaEngine Agreement.

Under the PharmaEngine Agreement, the Company is also obligated to pay PharmaEngine royalties on Baxalta’s net sales of ONIVYDE in the Licensed Territory. The Company records these royalty expenses in the period that the related sales occur, and such royalty expenses are recorded as a component of “Cost of revenues” within the consolidated statements of operations and comprehensive loss. During the year ended December 31, 2016, the Company recorded $0.1 million of royalty expenses related to PharmaEngine.

In August 2015, the Company and PharmaEngine also entered into a commercial supply agreement (the “PharmaEngine Supply Agreement”) pursuant to which the Company supplies ONIVYDE to PharmaEngine. The Company began supplying ONIVYDE under the PharmaEngine Supply Agreement in the second quarter of 2016 and recognized $0.3 million of revenue during the year ended December 31, 2016. No revenue related to the PharmaEngine Supply Agreement was recognized during the year ended December 31, 2015.

Actavis

In November 2013, the Company and Watson Laboratories, Inc. (“Actavis”) entered into a development, license and supply agreement (the “Actavis Agreement”) pursuant to which the Company will develop, manufacture and exclusively supply the bulk form of doxorubicin hydrochloride (HCl) liposome injection (the “Initial Product”) to Actavis. The Actavis Agreement was subsequently amended in January 2015 to transfer certain responsibilities from the Company to Actavis in exchange for reducing the aggregate milestone payments that the Company is eligible to receive by $0.4 million. The Company will manufacture and supply the Initial Product to Actavis in bulk form at an agreed upon unit price, and Actavis is responsible for all costs related to finished product processing and global commercialization. Pursuant to the agreement, additional products may be developed for Actavis in the future, the identities of which will be mutually agreed upon. The Company is eligible to receive up to $15.1 million in milestone and development payments, as well as additional reimbursement for specific activities performed by the Company at the request of Actavis. The Company will also receive a mid-twenties percentage of net profits on global sales of the Initial Product and any additional products. In October 2016, the U.S. Food and Drug Administration (the “FDA”) accepted for review an Abbreviated New Drug Application filed by Actavis for the Initial Product, which triggered the payment obligation of $1.1 million of milestones from Actavis to the Company. As of December 31, 2016, the Company had received $4.9 million in total milestone and development payments and reimbursement for specific activities from Actavis.

The Actavis Agreement will expire with respect to the Initial Product and any additional products developed in the future ten years after Actavis’ first sale of the applicable product, unless terminated earlier, and will automatically renew for additional two year periods thereafter unless either party provides notice of non-renewal. Either party may terminate the Actavis Agreement in the event of an uncured material breach or bankruptcy filing by the other party. Actavis may also terminate the Actavis Agreement for convenience in specified circumstances upon 90 days’ prior written notice.

The Company applied revenue recognition guidance to determine whether the performance obligations under the Actavis Agreement, including the license, participation on steering committees, development services, and manufacturing and supply services could be accounted for separately or as a single unit of accounting. The Company determined that these obligations represent a single unit of accounting and will recognize revenue as product is supplied to Actavis. Therefore, the Company has recorded $5.1 million and $4.0 million of billed and billable milestones and development expenses related to the Actavis Agreement as deferred revenue as of December 31, 2016 and 2015, respectively. This revenue is expected to be recognized by the Company over the ten year period that begins after Actavis’ first sale of the applicable product under the Actavis Agreement.

Product Revenue Reserves and Allowances

12 Months Ended

Dec. 31, 2016

Product Revenue Reserves And Allowances [Abstract]

Product Revenue Reserves and Allowances

5. Product Revenue Reserves and Allowances

The following table summarizes activity in each of the product revenue reserve and allowance categories for the year ended December 31, 2016:

(in thousands)	Trade Allowances			Rebates and Chargeback Discounts			Product Returns			Other Incentives			Total
Balance at December 31, 2015	$	138		$	362		$	32		$	8		$	540
Provisions related to sales in the current year		1,900			5,928			397			5			8,230
Adjustments related to sales in the prior year		—			(213	)		—			—			(213	)
Credits and payments made		(1,507	)		(5,077	)		(26	)		(7	)		(6,617	)
Balance at December 31, 2016	$	531		$	1,000		$	403		$	6		$	1,940

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2016

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

6. Fair Value of Financial Instruments

Fair value is an exit price, representing the amount that would be received from the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value is determined based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect certain market assumptions. As a basis for considering such assumptions, GAAP establishes a three-tier value hierarchy, which prioritizes the inputs used to develop the assumptions and for measuring fair value as follows: (Level 1) observable inputs such as quoted prices in active markets for identical assets; (Level 2) inputs other than the quoted prices in active markets that are observable either directly or indirectly; and (Level 3) unobservable inputs in which there is little or no market data, which requires the Company to develop its own assumptions. This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value.

Recurring Fair Value Measurements

The carrying values of cash, restricted cash, prepaid expenses, accounts receivable, accounts payable and accrued expenses, and other short-term assets and liabilities approximate their respective fair values due to the short-term maturities of these assets and liabilities.

The following tables summarize assets and liabilities measured at fair value on a recurring basis as of December 31, 2016 and 2015 and the input categories associated with those assets and liabilities:

	December 31, 2016
(in thousands)	Level 1		Level 2		Level 3
Assets:
Money market funds	$	12,373	$	—	$	—
Totals	$	12,373	$	—	$	—

Liabilities:
Silver Creek warrant liability	$	—	$	—	$	1,499
Totals	$	—	$	—	$	1,499

	December 31, 2015
(in thousands)	Level 1		Level 2		Level 3
Assets:
Money market funds	$	704	$	—	$	—
Totals	$	704	$	—	$	—

In December 2016, Silver Creek issued warrants to purchase an aggregate of 1.9 million shares of Silver Creek Series C preferred stock (the “Silver Creek warrants”). The issuance of the Silver Creek warrants is described more fully in Note 12, “Borrowings.” The Silver Creek warrants were valued at $1.5 million as of December 31, 2016 using a Black-Scholes option pricing model, probability-weighted for different exercise scenarios. The key assumptions utilized in the Black-Scholes option pricing model as of December 31, 2016 were a risk-free interest rate of 2.3%, expected dividend yield of 0.0%, expected volatility of 61.7% and expected term of 6.9 years. Changes in the fair value of the Silver Creek warrants in subsequent periods will be recognized as a component of “Other income, net” in the consolidated statements of operations and comprehensive loss.

There were no changes in valuation techniques or transfers between the fair value measurement levels during the years ended December 31, 2016 or 2015. There were no liabilities measured at fair value on a recurring basis as of December 31, 2015.

Non-Recurring Fair Value Measurements

Certain assets, including IPR&D intangible assets, may be measured at fair value on a non-recurring basis in periods subsequent to initial recognition. As described more fully in Note 9, “Goodwill and Intangible Assets, Net,” the Company performed an interim impairment assessment during the fourth quarter of 2016 on the Company’s IPR&D asset related to the antibody-targeted nanotherapeutic that contains a chemotherapy drug. The Company utilized a probability-weighted discounted cash flow analysis under the income approach in performing this assessment. As a result of this interim impairment assessment, the fair value of this IPR&D asset was determined to be zero as of December 31, 2016. No non-recurring fair value measurements were required during the year ended December 31, 2015.

Other Fair Value Measurements

The estimated fair value of the Convertible Notes was $57.5 million as of December 31, 2016. The Company estimated the fair value of the Convertible Notes by using a quoted market rate in an inactive market, which is classified as a Level 2 input. The carrying value of the Convertible Notes was $47.0 million as of December 31, 2016 due to the bifurcation of the conversion feature of the Convertible Notes as described more fully in Note 12, “Borrowings.”

As discussed in Note 12, “Borrowings,” in December 2015, the Company closed a private placement of $175.0 million aggregate principal amount of 11.50% senior secured notes due 2022 (the “2022 Notes”). The Company estimated the fair value of the 2022 Notes by using publicly-available information related to one of the 2022 Notes borrower’s portfolio of debt investments based on unobservable inputs, which is classified as a Level 3 input. The estimated fair value of the 2022 Notes was $167.0 million as of December 31, 2016. The carrying value of the 2022 Notes was $169.9 million as of December 31, 2016.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Marketable Securities	12 Months Ended
Marketable Securities	Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Marketable Securities	7. Marketable Securities As of both December 31, 2016 and 2015, the Company maintained only cash equivalents comprised of money market funds. As of December 31, 2016, the Company did not hold any securities that were in an unrealized loss position. There were no realized gains or losses on available-for-sale securities during the years ended December 31, 2016, 2015 or 2014.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Inventory

12 Months Ended

Dec. 31, 2016

Inventory Disclosure [Abstract]

Inventory

8. Inventory

Inventory as of December 31, 2016 and 2015 consisted of the following:

	December 31,
(in thousands)	2016		2015
Raw materials	$	4,483	$	900
Work in process		8,651		2,743
Finished goods		1,420		74
Total inventory	$	14,554	$	3,717

Inventory acquired prior to receipt of marketing approval of ONIVYDE was expensed as research and development expense as incurred. The Company began to capitalize the costs associated with the production of ONIVYDE upon receipt of FDA approval on October 22, 2015.

During the year ended December 31, 2016, the Company incurred aggregate charges of $3.6 million related to excess and scrap inventory and excess manufacturing capacity. These expenses were recorded as a component of “Cost of revenues.”

Goodwill and Intangible Assets, Net

12 Months Ended

Dec. 31, 2016

Goodwill And Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets, Net

9. Goodwill and Intangible Assets, Net

As part of the acquisition of Hermes BioSciences, Inc. (“Hermes”) on October 6, 2009, the Company recognized goodwill of $3.6 million and acquired IPR&D assets of $7.0 million related to several development programs: an antibody-targeted nanotherapeutic that contains a chemotherapy drug, a nanotherapeutic that contains a chemotherapy drug and other early-stage preclinical programs in the amounts of $2.8 million, $3.4 million and $0.8 million, respectively. The Company also acquired intangible assets of $3.2 million related to core nano-carrier technology. These values were determined at the time of acquisition by estimating the costs to develop the acquired IPR&D assets into commercially viable products, estimating the net cash flows from such projects and discounting the net cash flows back to their present values. The probability of success factors and discount rates used for each project considered the uncertainty surrounding the successful development of the acquired IPR&D assets.

The deprioritization and delay of the other early-stage preclinical programs during the year ended December 31, 2013 resulted in an impairment charge of $0.8 million recognized during the third quarter of 2013.

During the fourth quarter of 2015, upon the approval of ONIVYDE by the FDA, the Company reclassified the acquired IPR&D asset related to the nanotherapeutic that contains a chemotherapy drug to definite-lived intangible assets and commenced amortization. This definite-lived ONIVYDE intangible asset is amortized on a straight-line basis through 2028.

In December 2016, the Company determined that it would be stopping the ongoing Phase 2 clinical trial of MM-302, which utilized the antibody-targeted nanotheraputic that contains a chemotherapy drug. The decision to stop the trial was made following an independent Data and Safety Monitoring Board (the “DSMB”) opinion that continuing the clinical trial would be unlikely to demonstrate benefit over the comparator treatments. Subsequent to this recommendation, a futility assessment was performed that confirmed the DSMB’s opinion. Both the treatment and control arms were found to have shorter than expected median progression free survival. While patients currently enrolled in the clinical trial may choose to continue on their assigned treatment based upon discussion with their study physician, no further development of MM-302 is being contemplated by the Company at this time. As a result of this determination, the Company recorded an impairment charge of $2.8 million during the fourth quarter of 2016. This impairment charge was recorded as a component of “Research and development expenses” within the consolidated statements of operations and comprehensive loss.

The core nano-carrier technology intangible asset is being amortized on a straight-line basis over a period of ten years, which is the Company’s best estimate of the useful life of this technology.

The Company has not recorded any impairment charges related to either goodwill or definite-lived intangible assets during the years ended December 31, 2016, 2015 and 2014.

Goodwill and intangible assets as of December 31, 2016 and 2015 consisted of the following:

	December 31, 2016
(in thousands)	Gross Carrying Value		Accumulated Amortization			Net Carrying Value
Nano-carrier technology intangible asset	$	3,200	$	(2,315	)	$	885
ONIVYDE intangible asset		3,400		(308	)		3,092
Goodwill		3,605		—			3,605
Totals	$	10,205	$	(2,623	)	$	7,582

	December 31, 2015
(in thousands)	Gross Carrying Value		Accumulated Amortization			Net Carrying Value
Nano-carrier technology intangible asset	$	3,200	$	(1,995	)	$	1,205
ONIVYDE intangible asset		3,400		(50	)		3,350
IPR&D		2,800		—			2,800
Goodwill		3,605		—			3,605
Totals	$	13,005	$	(2,045	)	$	10,960

Amortization expense was $0.6 million, $0.4 million and $0.3 million for the years ended December 31, 2016, 2015 and 2014, respectively. The weighted-average remaining amortization period for the Company’s intangible assets subject to amortization is approximately 10.0 years as of December 31, 2016.

Future amortization expense for the next five-year period is expected to be as follows:

Years Ended December 31,	(in thousands)
2017	$	578
2018		578
2019		503
2020		258
2021		258

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2016

Property Plant And Equipment [Abstract]

Property and Equipment, Net

10. Property and Equipment, Net

Property and equipment, net as of December 31, 2016 and 2015 consisted of the following:

	December 31,
(in thousands)	2016			2015
Lab equipment	$	20,752		$	19,305
IT equipment		8,601			7,742
Leasehold improvements		21,153			21,026
Furniture and fixtures		959			910
Construction in process		515			2,243
Total property and equipment, gross		51,980			51,226
Less: Accumulated depreciation		(36,215	)		(29,311	)
Total property and equipment, net	$	15,765		$	21,915

Depreciation expense was $7.3 million, $5.5 million and $4.2 million for the years ended December 31, 2016, 2015 and 2014, respectively. Capitalized interest costs were insignificant for the years ended December 31, 2016, 2015 and 2014.

During the year ended December 31, 2016, the Company recognized a $0.5 million charge related to the disposal of property and equipment. There were no significant losses recognized related to the disposal of property and equipment during the years ended December 31, 2015 or 2014.

Accounts Payable, Accrued Expenses and Other

12 Months Ended

Dec. 31, 2016

Payables And Accruals [Abstract]

Accounts Payable, Accrued Expenses and Other

11. Accounts Payable, Accrued Expenses and Other

Accounts payable, accrued expenses and other as of December 31, 2016 and 2015 consisted of the following:

	December 31,
(in thousands)	2016		2015
Accounts payable	$	3,384	$	5,049
Accrued goods and services		15,760		14,295
Accrued clinical trial costs		11,260		12,764
Accrued drug purchase costs		910		7,460
Accrued payroll and related benefits		9,150		9,009
Accrued restructuring expenses		774		—
Accrued asset sale transaction costs		3,724		—
Accrued interest		2,100		3,041
Accrued dividends payable		19		19
Silver Creek warrant liability		1,499		—
Deferred tax incentives		1,402		445
Total accounts payable, accrued expenses and other	$	49,982	$	52,082

Borrowings

12 Months Ended

Dec. 31, 2016

Debt Disclosure [Abstract]

Borrowings

12. Borrowings

2022 Notes

On December 22, 2015, the Company closed a private placement of $175.0 million aggregate principal amount of 11.50% 2022 Notes and entered into an indenture (the “U.S. Bank Indenture”) with U.S. Bank National Association as trustee and collateral agent (the “2020 Notes Trustee”). As a result of this placement, the Company received net proceeds of approximately $168.5 million, after deducting private placement and offering expenses payable by the Company. The private placement and offering expenses included $0.9 million of transaction costs that were expensed in accordance with the debt modification guidance per ASC 470, Debt, as further discussed below. The 2022 Notes bear interest at a rate of 11.50% per year, payable semi-annually on June 15 and December 15 of each year, beginning on June 15, 2016. The Company will pay semi-annual installments of principal on the 2022 Notes of $21,875,000 each, subject to adjustment as provided in the 2022 Notes, on June 15 and December 15 of each year, beginning on June 15, 2019. The 2022 Notes will mature on December 15, 2022, unless earlier redeemed or repurchased in accordance with their terms prior to such date.

The Company may redeem the 2022 Notes at its option, in whole or in part from time to time at a price equal to the principal amount plus accrued interest and a specified make-whole premium. If the Company experiences certain change of control events as defined in the U.S. Bank Indenture, the holders of the 2022 Notes will have the right to require the Company to purchase all or a portion of the 2022 Notes at a purchase price in cash equal to 101% of the principal amount thereof, plus accrued and unpaid interest to the date of purchase. In addition, upon certain asset sale events as defined in the U.S. Bank Indenture, the Company may be required to offer to use the net proceeds thereof to purchase all or a portion of the 2022 Notes at 100% of the principal amount thereof, plus accrued and unpaid interest to the date of purchase.

The 2022 Notes are senior secured obligations of the Company and will be equal in right of payment to all existing and future pari passu indebtedness of the Company (including the Company’s outstanding Convertible Notes), will be senior in right of payment to all existing and future subordinated indebtedness of the Company, will have the benefit of a security interest in the 2022 Notes collateral and will be junior in lien priority in respect of any asset-based lending collateral that secures any first priority lien obligations from time to time. The 2022 Notes contain customary covenants, including covenants that limit or restrict the Company’s ability to incur liens, incur indebtedness, and make certain restricted payments, but do not contain covenants related to future financial performance. The 2022 Notes are secured by a first priority lien on substantially all of the Company’s assets.

The 2022 Notes contain customary events of default. Upon certain events of default occurring, the 2022 Notes Trustee may declare 100% of the principal of and accrued and unpaid interest, if any, on all the 2022 Notes to be due and payable. In the case of certain events of bankruptcy, insolvency or reorganization involving the Company or a restricted subsidiary, 100% of the principal of, and accrued and unpaid interest on, the 2022 Notes will automatically become due and payable. There have been no events of default as of or during the year ended December 31, 2016.

The Company assessed the 2022 Notes pursuant to ASC 815, Derivatives and Hedging, to determine if any features necessitated bifurcation from the host instrument. The Company concluded that none of the embedded redemption features within the 2022 Notes require bifurcation, as these features are clearly and closely related to the host instrument.

Debt issuance costs incurred by the Company, excluding costs allocated to the debt modification as discussed below, are accounted for as a direct deduction to the carrying value of the 2022 Notes and are amortized to interest expense using the effective interest method over the life of the 2022 Notes. The effective interest rate associated with the 2022 Notes is 12.32%. For the years ended December 31, 2016 and 2015, interest expense related to the 2022 Notes was approximately $20.9 million and $0.5 million, respectively.

Convertible Notes

In July 2013, the Company issued $125.0 million aggregate principal amount of Convertible Notes in an underwritten public offering. The Company issued the Convertible Notes under an indenture, dated as of July 17, 2013 (the “Base Indenture”) between the Company and Wells Fargo Bank, National Association, as trustee (the “Convertible Notes Trustee”), as supplemented by a supplemental indenture, dated as of July 17, 2013, between the Company and the Convertible Notes Trustee (together with the Base Indenture, the “Wells Fargo Indenture”). As a result of the Convertible Notes offering, the Company received net proceeds of approximately $120.6 million, after deducting underwriting discounts and commissions and offering expenses payable by the Company.

The Convertible Notes bear interest at a rate of 4.50% per year, payable semiannually in arrears on January 15 and July 15 of each year, beginning on January 15, 2014. The Convertible Notes are general unsecured senior obligations of the Company and rank (i) pari passu in seniority with respect to the 2022 Notes, (ii) senior in right of payment to any of the Company’s indebtedness that is expressly subordinated in right of payment to the Convertible Notes, (iii) equal in right of payment to any of the Company’s unsecured indebtedness that is not so subordinated, (iv) effectively junior in right of payment to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness and (v) structurally junior to all indebtedness and other liabilities (including trade payables) of the Company’s subsidiaries.

The Company separately accounted for the liability and equity components of the Convertible Notes by bifurcating gross proceeds between the indebtedness, or liability component, and the embedded conversion option, or equity component. This bifurcation was done by estimating an effective interest rate as of the date of issuance for similar notes which do not contain an embedded conversion option. The gross proceeds received from the issuance of the Convertible Notes less the initial amount allocated to the indebtedness resulted in a $53.8 million allocation to the embedded conversion option. The embedded conversion option was recorded in stockholders’ deficit and as debt discount, to be subsequently amortized as interest expense over the term of the Convertible Notes. Underwriting discounts and commissions and offering expenses totaled $4.4 million and were allocated to the indebtedness and the embedded conversion option based on their relative values.

On April 13, 2016, the Company entered into separate, privately-negotiated conversion agreements (the “Conversion Agreements”) with certain holders of the Convertible Notes. Under the Conversion Agreements, such holders agreed to convert an aggregate principal amount of $64.2 million of Convertible Notes held by them. The Company initially settled each $1,000 principal amount of Convertible Notes surrendered for conversion by delivering 136 shares of the Company’s common stock on April 18, 2016. In total, the Company issued an aggregate of 8,732,152 shares of its common stock on this initial closing date. In addition, pursuant to the Conversion Agreements, at the additional closings (as defined in the Conversion Agreements), the Company issued an aggregate of 3,635,511 shares of the Company’s common stock representing an aggregate of $27.7 million as additional payments in respect of the conversion of the Convertible Notes. The number of additional shares was determined based on the daily VWAP (as defined in the Conversion Agreements) of the Company’s common stock for each of the trading days in the 10-day trading period following the date of the Conversion Agreements. The issuance of 12,367,663 total shares of the Company’s common stock pursuant to the Conversion Agreements resulted in an increase to common stock and additional paid-in capital of $101.0 million.

As a result of the conversion, the Company recognized an overall loss on extinguishment of $14.6 million representing the difference between the total settlement consideration transferred to the holders that was attributed to the liability component of the Convertible Notes, based on the fair value of that component at the time of conversion, and the net carrying value of the liability. The loss on extinguishment was recorded as interest expense during the second quarter of 2016. The remaining settlement consideration transferred was allocated to the reacquisition of the embedded conversion option and recognized as a $39.8 million reduction of additional paid-in capital. Transaction costs incurred with third parties related to the conversion were allocated to the liability and equity components and resulted in an additional $0.2 million of interest expense and a $0.2 million reduction of additional paid-in capital.

The outstanding Convertible Notes will mature on July 15, 2020 (the “Maturity Date”), unless earlier repurchased by the Company or converted at the option of holders. Holders may convert their Convertible Notes at their option at any time prior to the close of business on the business day immediately preceding April 15, 2020 only under the following circumstances:

•

during any calendar quarter commencing after September 30, 2013 (and only during such calendar quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day;

•

during the five business day period after any five consecutive trading day period (the “measurement period”) in which the trading price (as defined in the Convertible Notes) per $1,000 principal amount of Convertible Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day; or

•

upon the occurrence of specified corporate events set forth in the Wells Fargo Indenture.

On or after April 15, 2020 until the close of business on the business day immediately preceding the Maturity Date, holders may convert their Convertible Notes at any time, regardless of the foregoing circumstances.

Following the repayment and satisfaction in full of the Company’s obligations to Hercules under the Loan Agreement, which occurred in December 2015, upon any conversion of the Convertible Notes, the Convertible Notes may be settled, at the Company’s election, in cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock.

The initial conversion rate of the Convertible Notes is 160 shares of the Company’s common stock per $1,000 principal amount of Convertible Notes, which is equivalent to an initial conversion price of $6.25 per share of common stock. The conversion rate will be subject to adjustment in some events, but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the Maturity Date, the Company will increase the conversion rate for a holder who elects to convert its Convertible Notes in connection with such a corporate event in certain circumstances.

Upon the occurrence of a fundamental change (as defined in the Wells Fargo Indenture) involving the Company, holders of the Convertible Notes may require the Company to repurchase all or a portion of their Convertible Notes for cash at a price equal to 100% of the principal amount of the Convertible Notes to be purchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

The Wells Fargo Indenture contains customary terms and covenants and events of default with respect to the Convertible Notes. If an event of default (as defined in the Wells Fargo Indenture) occurs and is continuing, the Convertible Notes Trustee by written notice to the Company, or the holders of at least 25% in aggregate principal amount of the Convertible Notes then outstanding by written notice to the Company and the Convertible Notes Trustee, may, and the Convertible Notes Trustee at the request of such holders will, declare 100% of the principal of and accrued and unpaid interest on the Convertible Notes to be due and payable. In the case of an event of default arising out of certain events of bankruptcy, insolvency or reorganization involving the Company or a significant subsidiary (as set forth in the Indenture), 100% of the principal of and accrued and unpaid interest on the Convertible Notes will automatically become due and payable. There have been no events of default as of or during the year ended December 31, 2016.

For the years ended December 31, 2016, 2015 and 2014, interest expense related to the Convertible Notes was $22.7 million, $13.7 million and $13.7 million, respectively. As discussed above, interest expense for the year ended December 31, 2016 includes the loss on extinguishment of $14.6 million associated with the April 2016 conversion of the Convertible Notes as well as $0.2 million of related transaction costs.

Loan Agreement

In November 2012, the Company entered into the Loan Agreement with Hercules pursuant to which the Company received loans in the aggregate principal amount of $40.0 million. The Company, as permitted under the Loan Agreement, had previously extended the interest-only payment period with the aggregate principal balance of the loans to be repaid in monthly installments starting on June 1, 2014 and continuing through November 1, 2016. On June 25, 2014, the Company entered into an amendment to the Loan Agreement, whereby the Company and Hercules agreed to extend until October 1, 2014 the period during which the Company makes interest-only payments. On November 6, 2014, the Company entered into a further amendment to the Loan Agreement, whereby the Company and Hercules agreed to extend by four additional months the period during which the Company makes interest-only payments. On February 25, 2015, the Company entered into a fourth amendment to the Loan Agreement pursuant to which the Company and Hercules agreed to extend the maturity date and the period during which the Company makes interest-only payments on its current loans in the aggregate principal amount of $40.0 million. As a result of this amendment, the Company was required to repay the outstanding aggregate principal balance of the loan beginning on June 1, 2016 and continuing through November 1, 2018. As a result of the FDA’s approval of the Company’s NDA for ONIVYDE, which occurred on October 22, 2015, the Company elected to extend the interest-only period by an additional six months such that the Company would repay the outstanding aggregate principal balance of the loans beginning on December 1, 2016 and continuing through November 1, 2018. This amendment was treated as a debt modification for accounting purposes.

Upon the earlier of full repayment of the loans or November 1, 2016, the Company was required to pay Hercules a fee of $1.2 million, which had been recorded as a discount to the loans and as a long-term liability on the Company’s consolidated balance sheets. Additionally, the Company reimbursed Hercules for costs incurred related to the loans, which was reflected as a discount to the carrying value of the loans. The Company amortized these loan discounts totaling $1.6 million to interest expense over the term of the loans using the effective interest method.

In connection with the Loan Agreement, the Company granted Hercules a security interest in all of the Company’s personal property now owned or hereafter acquired, excluding intellectual property but including the proceeds from the sale, if any, of intellectual property, and a negative pledge on intellectual property. The Loan Agreement also contained certain representations, warranties and non-financial covenants of the Company.

During the fourth quarter of 2015, the Company repaid the loans in full in conjunction with the issuance of the 2022 Notes. The total repayment amount included the $40.0 million in outstanding principal, the $1.2 million fee discussed above and interest accrued up through the repayment date. The Company assessed the repayment of the Loan Agreement with Hercules in conjunction with the issuance of the 2022 Notes, of which Hercules holds a portion, in accordance with the debt extinguishment and modification guidance per ASC 470, Debt. Based upon this assessment, the Company concluded that this transaction represented a debt modification, and accordingly, $0.3 million of unamortized debt issuance costs related to the Loan Agreement are being amortized as an adjustment of interest expense over the life of the 2022 Notes using the effective interest method. In addition, $0.9 million of debt issuance costs associated with the 2022 Notes were allocated to the modified Loan Agreement and expensed as a component of “Interest expense” on the consolidated statement of operations and comprehensive loss for the year ended December 31, 2015.

For the years ended December 31, 2015 and 2014, interest expense related to the Hercules loans was $5.4 million and $4.7 million, respectively. No interest expense related to the Hercules loans was recognized during the year ended December 31, 2016.

Credit Facility

On November 8, 2016, the Company entered into a Loan and Security Agreement (the “Credit Agreement”) with BioPharma Credit Investments IV Sub, LP (“Pharmakon”) pursuant to which a credit facility of an aggregate principal amount of at least $15.0 million and up to $25.0 million is available. The credit facility was originally available at any time through March 15, 2017 upon the Company’s request and upon compliance with certain funding conditions. As described more fully in Note 23, “Subsequent Events,” the availability of the credit facility was subsequently extended through April 27, 2017. If the Company borrows under the Credit Agreement, the credit facility will bear interest at an annual rate of 11.50%.

In connection with any borrowings that occur under the Credit Agreement, the Company will grant Pharmakon a security interest in all inventory and accounts receivable. The Credit Agreement also contains certain representations, warranties and non-financial covenants. In addition, the Credit Agreement grants Pharmakon an option during the two years following funding of the credit facility to participate in a future financing at an amount up to the lesser of 25% of the total amount financed or $50.0 million. The Company had not borrowed any amounts under the Credit Agreement as of December 31, 2016.

Silver Creek Convertible Notes

In December 2012, the Company’s majority owned subsidiary, Silver Creek, entered into a Note Purchase Agreement pursuant to which it issued convertible notes to various lenders in aggregate principal amounts of $1.6 million in December 2012, $0.9 million during the year ended December 31, 2013 and $1.0 million during the year ended December 31, 2014. The notes issued pursuant to the Note Purchase Agreement bore interest at 6% per annum. Upon issuance, these convertible notes contained a feature wherein if at any time prior to maturity Silver Creek enters into a qualifying equity financing, defined as a sale or series of related sales of equity securities prior to the maturity date and resulting in at least $4.0 million of gross proceeds, the notes would automatically convert into the next qualifying equity financing at a 25% discount. The Company determined that this convertible feature met the definition of a derivative and required separate accounting treatment. The derivative was estimated to be valued at $0.2 million using a probability-weighted model and was recorded as derivative liability on the consolidated balance sheets. For the year ended December 31, 2014, the derivative was remeasured upon conversion of the notes with the gain in remeasurement recognized in other income. The specific notes that were outstanding as of December 31, 2014 matured and converted, along with an immaterial amount of accrued interest into shares of Silver Creek Series A preferred stock on December 31, 2014.

In May 2016, Silver Creek issued an aggregate of $1.0 million of Silver Creek Notes. In August 2016, Silver Creek issued $0.2 million of additional Silver Creek Notes under the same terms as the May 2016 issuance. The Silver Creek Notes were automatically convertible into shares of Silver Creek equity under a variety of conversion scenarios. The Silver Creek Notes bore interest at 6% per annum and were set to mature and convert, along with accrued interest, into Silver Creek Series B preferred stock at a conversion price of $1.35 per share on December 31, 2016. If, prior to maturity, Silver Creek entered into a sale or series of related sales of equity securities resulting in at least $4.0 million of gross proceeds, the Silver Creek Notes would convert into the equity securities sold at the lesser of the price paid per share for the equity securities or $1.60 per share. Principal and accrued interest related to the Silver Creek Notes were not permitted to be paid in cash by Silver Creek without the consent of a majority of the noteholders.

In December 2016, Silver Creek executed a Series C Preferred Stock and Warrant Purchase Agreement (the “Silver Creek Series C Agreement”) whereby it agreed to sell 1.5 million shares of Silver Creek Series C preferred stock to new investors at a purchase price of $1.50 per share. In connection with this financing, holders of the Silver Creek Notes agreed to convert all principal and accrued interest associated with the Silver Creek Notes into 0.8 million shares of Silver Creek Series C preferred stock at a conversion price of $1.50 per share.

New purchasers of the Silver Creek Series C preferred stock also received warrants to purchase an aggregate of 1.9 million shares of Silver Creek Series C preferred stock at a future date. The exercise price of the warrants varies based upon the achievement of certain milestone events defined in the related warrant agreements. Milestone Event 1 is defined as the date that is seven business days following the acceptance by the FDA of Silver Creek’s filing of an Investigational New Drug application (“IND”), or 30 business days after the IND is filed without FDA rejection of the application. Milestone Event 2 is defined as the date that is seven business days following the date when Silver Creek completes a Phase 1 clinical trial provided, that if Silver Creek receives proceeds of less than $4.0 million pursuant to the sale of Series C preferred stock, Milestone Event 2 shall mean the date that is seven business days following the first dose in humans in a clinical trial.

Of the warrants to purchase 1.9 million shares of Silver Creek Series C preferred stock that were issued, warrants to purchase 1.2 million shares of Silver Creek Series C preferred stock are exercisable at an exercise price of $1.75 per share if the warrant is exercised prior to the date that is 30 business days after the date that the holder receives notice from Silver Creek of the achievement of Milestone Event 1, or $2.25 per share if the warrant is exercised on or after the date that is 30 business days after the holder receives notice from Silver Creek of the achievement of Milestone Event 1. The remaining warrants to purchase 0.7 million shares of Silver Creek Series C preferred stock are exercisable at an exercise price of $2.25 per share if the warrant is exercised prior to the date that is 30 business days after the date that the holder receives notice from Silver Creek of the achievement of Milestone Event 2, or $2.75 per share if the warrant is exercised on or after the date that is 30 business days after Milestone Event 2. All warrants to purchase Silver Creek Series C preferred stock are exercisable until the earliest of (i) the consummation of a Silver Creek liquidation event, (ii) the consummation of an initial public offering of Silver Creek common stock, (iii) four months after the achievement of Milestone Event 2 or (iv) seven years from the date of issuance.

The warrants to purchase Silver Creek Series C preferred stock were classified as a current liability in accordance with ASC 480, Distinguishing Liabilities from Equity, and initially measured at fair value, as described more fully in Note 6, “Fair Value of Financial Instruments.” The fair value of the warrants was deducted from the total Silver Creek Series C preferred stock proceeds received by Silver Creek, and the remaining proceeds received were allocated to the Silver Creek Series C preferred stock.

Future Minimum Payments under Outstanding Borrowings

Future minimum payments under outstanding borrowings as of December 31, 2016 are as follows:

(in thousands)	Convertible Notes			2022 Notes
2017	$	2,736		$	20,125
2018		2,736			20,125
2019		2,736			62,617
2020		63,527			57,586
2021 and thereafter		—			100,078
Total		71,735			260,531
Less interest		(10,943	)		(85,531	)
Less unamortized discount		(13,842	)		(5,089	)
Less current portion		—			—
Long-term debt	$	46,950		$	169,911

Restructuring Activities

12 Months Ended

Dec. 31, 2016

Restructuring And Related Activities [Abstract]

Restructuring Activities

13. Restructuring Activities

On October 3, 2016, the Company announced a 22% reduction in headcount as part of a major corporate restructuring with the objective of prioritizing its research and development on a focused set of systems biology-derived oncology products and strengthening its financial runway. On this same date, the Company also announced the resignation of Robert Mulroy, the Company’s former President and Chief Executive Officer (“CEO”).

Under this corporate restructuring, the Company recognized total restructuring expenses of $5.9 million during the year ended December 31, 2016 related to stock-based compensation expense for certain terminated employees, contractual termination benefits for employees with pre-existing severance arrangements and one-time employee termination benefits. These one-time employee termination benefits were comprised of severance, benefits and related costs, all of which resulted in cash expenditures during the third and fourth quarters of 2016.

The following table summarizes the charges related to the restructuring activities as of December 31, 2016:

(in thousands)

Expenses

Less: Payments

Less: Non-Cash Expenses

Accrued Restructuring Expenses at

December 31, 2016

Severance, benefits and related costs due

to workforce reduction

5,856

(3,711

)

(1,371

)

774

Totals

5,856

(3,711

)

(1,371

)

774

Common Stock Warrants

12 Months Ended

Dec. 31, 2016

Text Block [Abstract]

Common Stock Warrants

14. Common Stock Warrants

The following is a description of the common stock warrant activity of the Company:

(in thousands, except per share amounts)	Warrants for the Purchase of Common Stock			Weighted Average Exercise Price
Balance at December 31, 2013		2,777		$	3.05
Exercised		(396	)	$	3.38
Balance at December 31, 2014		2,381		$	3.00
Exercised		(2,355	)	$	3.00
Cancelled		(26	)	$	3.00
Balance at December 31, 2015		—		$	—

During the year ended December 31, 2014, warrants to purchase approximately 75,000 shares of common stock were cashless exercised and 38,000 shares of common stock were issued. During the year ended December 31, 2015, warrants to purchase approximately 2,295,000 shares of common stock were cashless exercised and 1,695,000 shares of common stock were issued. As of December 31, 2015, all remaining unexercised warrants for the purchase of common stock had expired and were cancelled.

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2016
Equity [Abstract]
Common Stock	15. Common Stock In July 2015, the Company entered into a Sales Agreement with Cowen and Company, LLC (“Cowen”) to sell shares of the Company’s common stock having an aggregate sales price of up to $40.0 million through an “at the market offering” program under which Cowen acted as the sales agent. The Company concluded sales under this program in September 2015, having sold approximately 3.8 million shares of common stock and generating approximately $38.6 million in net proceeds, after deducting commissions and offering expenses. As of December 31, 2016 and 2015, the Company had 200.0 million shares of $0.01 par value common stock authorized. There were approximately 130.2 million and 115.9 million shares of common stock issued and outstanding as of December 31, 2016 and 2015, respectively.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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+ Details

Stock-Based Compensation

12 Months Ended

Dec. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

16. Stock-Based Compensation

In 2008, the Company adopted the 2008 Stock Incentive Plan (as amended, the “2008 Plan”) for employees, officers, directors, consultants and advisors. The 2011 Stock Incentive Plan (the “2011 Plan”) became effective upon closing of the Company’s initial public offering in April 2012. Upon effectiveness of the 2011 Plan, no further awards were available to be issued under the 2008 Plan. The 2011 Plan is administered by the Board of Directors of the Company and permits the Company to grant incentive and non-qualified stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. Additional shares also become available for grant by reason of the forfeiture, cancellation, expiration or termination of existing awards. The Company registered 4.1 million, 3.7 million and 3.6 million of additional shares of common stock related to the 2011 Plan in February 2016, February 2015 and March 2014, respectively. As of December 31, 2016, there were 4.7 million shares remaining available for grant under the 2011 Plan.

During the years ended December 31, 2016, 2015 and 2014, the Company issued options to purchase 4.3 million, 3.7 million and 3.9 million shares of common stock, respectively. These options generally vest over a three-year period for employees. Options granted to directors vest immediately.

The fair value of stock options granted to employees during the years ended December 31, 2016, 2015 and 2014 was estimated at the date of grant using the following assumptions:

	Years Ended December 31,
	2016	2015	2014
Risk-free interest rate	1.1 – 2.0%	1.5 – 1.8%	1.6 – 2.0%
Expected dividend yield	0%	0%	0%
Expected term	5.0 – 5.8 years	5.0 – 5.9 years	5.0 – 5.9 years
Expected volatility	67 – 69%	66 – 67%	64 – 72%

The Company uses the simplified method to calculate the expected term as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term of its stock options. Under this approach, the expected term is calculated to be the average of the ten-year contractual term of the option and the weighted-average vesting term of the option, taking into consideration multiple vesting tranches. The computation of expected volatility is based on the historical volatility of comparable companies from a representative peer group selected based on industry and market capitalization. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected life of the stock options. Management estimates expected forfeitures based on historical experience and recognizes compensation costs only for those equity awards expected to vest.

The Company recognized stock-based compensation expense during the years ended December 31, 2016, 2015 and 2014 as follows:

	Years Ended December 31,
(in thousands)	2016			2015		2014
Employee awards:
Research and development expense	$	6,503		$	8,271	$	6,864
Selling, general and administrative expense		7,331			7,022		6,065
Restructuring expense		1,371			—		—
Stock-based compensation expense for employee awards		15,205			15,293		12,929
Stock-based compensation expense for non-employee awards		1			58		268
Less: stock-based compensation expense capitalized to inventory		(341	)		—		—
Total stock-based compensation expense	$	14,865		$	15,351	$	13,197

The following table summarizes stock option activity during the year ended December 31, 2016:

(in thousands, except per share amounts)	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2015		19,211		$	5.72		6.24	$	47,963
Granted		4,258		$	5.57
Exercised		(1,958	)	$	3.29
Forfeited		(2,487	)	$	7.04
Outstanding at December 31, 2016		19,024		$	5.77		5.97	$	7,564
Vested and expected to vest at December 31, 2016		18,794		$	5.76		5.93	$	7,564
Exercisable at December 31, 2016		14,968		$	5.49		5.24	$	7,564

The weighted-average grant date fair value of stock options granted during the years ended December 31, 2016, 2015 and 2014 was $3.32, $5.80 and $3.41, respectively.

The aggregate intrinsic value was calculated as the difference between the exercise price of the stock options and the fair value of the underlying common stock. The aggregate intrinsic value of options exercised during the years ended December 31, 2016, 2015 and 2014 was $5.6 million, $30.9 million and $19.8 million, respectively.

As of December 31, 2016, there was $12.7 million of total unrecognized stock-based compensation expense related to unvested employee stock options. The Company expects to recognize this expense over a weighted-average period of approximately 1.7 years.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Income Taxes

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Income Taxes

17. Income Taxes

As a result of losses incurred, the Company did not provide for any income taxes in the years ended December 31, 2016, 2015 or 2014. A reconciliation of the Company’s effective tax rate to the statutory federal income tax rate is as follows:

	Years Ended December 31,
	2016			2015			2014
Federal income tax at statutory federal rate		35.0	%		35.0	%		35.0	%
State taxes		0.7			1.0			3.1
Permanent differences		(11.6	)		(6.4	)		(9.1	)
Stock-based compensation		(2.2	)		(1.3	)		(1.7	)
Tax credits		28.0			21.3			30.5
Foreign rate differential		—			—			(2.3	)
Change in deferred state tax rate		(0.3	)		(2.3	)		—
Other		4.5			(0.5	)		4.5
Change in valuation allowance		(54.1	)		(46.8	)		(60.0	)
Total		—	%		—	%		—	%

During the year ended December 31, 2014, the Company recorded a deferred tax liability related to the embedded conversion option of the Convertible Notes though equity. This deferred tax liability is reflected in the deferred tax table below, but is appropriately excluded from the effective tax rate.

Temporary differences that give rise to significant net deferred tax assets as of December 31, 2016 and 2015 are as follows:

	December 31,
(in thousands)	2016			2015
Deferred tax assets
Net operating losses	$	194,027		$	182,992
Capitalized research and development expenses		15,854			21,444
Credit carryforwards		144,823			93,113
Depreciation		2,557			2,128
Deferred compensation		12,463			11,664
Accrued expenses		3,601			1,807
Deferred revenue		21,935			10,999
Other temporary differences		25,276			17,235
Total gross deferred tax assets		420,536			341,382
Valuation allowance		(414,558	)		(326,577	)
Net deferred tax assets		5,978			14,805
Deferred tax liabilities
Intangible assets		(1,428	)		(2,667	)
Debt discount		(4,550	)		(12,138	)
Net deferred taxes	$	—		$	—

The Company concluded that there are no significant uncertain tax positions requiring recognition in the consolidated financial statements. The Company’s evaluation was performed for the tax years ended December 31, 2013 through 2016, the tax years which remain subject to examination by major tax jurisdictions as of December 31, 2016. However, to the extent the Company utilizes net operating losses from years prior to 2012, the statute remains open to the extent of the net operating losses utilized. The Company’s policy is to recognize interest and penalties for uncertain tax positions as a component of income tax expense. The Company has not recognized any interest and penalties historically through December 31, 2016.

At December 31, 2016, the Company had net operating loss carryforwards for federal and state income tax purposes of $542.7 million and $367.4 million, respectively. Included in the federal and state net operating loss carryforwards is approximately $39.2 million and $25.2 million, respectively, of deduction related to the exercise of stock options. This amount represents an excess tax benefit, which will be realized when it results in reduction of cash taxes in accordance with ASC 718, Compensation – Stock Compensation. The Company’s existing federal and state net operating loss carryforwards will expire in years through 2036. The Company also has available research and development credits for federal and state income tax purposes of approximately $27.3 million and $16.3 million, respectively. The federal and state research and development credits will begin to expire in 2022 and 2025, respectively. As of December 31, 2016, the Company also had available investment tax credits for state income tax purposes of $0.8 million, which will expire in years through 2019 if unused. In addition, the Company has federal orphan drug credits of $106.4 million which begin to expire in 2031. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are comprised principally of net operating loss carryforwards, deferred revenue and capitalized research and development expenses. Under the applicable accounting standards, the Company has considered its history of losses and concluded that it is more likely than not that the Company will not recognize the benefits of federal and state deferred tax assets. Accordingly, the Company has established a full valuation allowance against the deferred tax assets. If the asset sale with Ipsen, which is outlined more fully in Note 23, “Subsequent Events,” is consummated, the Company expects to utilize deferred tax assets to offset the taxable gain generated by the sale. The valuation allowance could be released during the year ended December 31, 2017 once it is determined it is more likely than not that the deferred tax assets will be realizable.

Utilization of the net operating loss and research and development credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”), due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of net operating loss and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax. The Company completed an evaluation of ownership changes through September 30, 2016 to assess whether utilization of the Company’s net operating loss or research and development credit carryforwards would be subject to an annual limitation under Section 382 of the Internal Revenue Code. The Company believes that it may be able to utilize all of its tax attributes as a result of the analysis. To the extent an ownership change occurs in the future, the net operating loss and credit carryforwards may be subject to limitation.

The Company has not yet conducted a study of its domestic research and development credit carryforwards and orphan drug credits. This study may result in an increase or decrease to the Company’s credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. As a result, there would be no impact to the consolidated statements of operations and comprehensive loss or consolidated statements of cash flows if an adjustment were required.

The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2016, 2015 and 2014 was as follows:

(in thousands)	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
December 31, 2014	$	207,304	$	50,185	$	—	$	257,489
December 31, 2015		257,489		69,088		—		326,577
December 31, 2016		326,577		87,981		—		414,558

Commitments and Contingencies

12 Months Ended

Dec. 31, 2016

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

18. Commitments and Contingencies

Operating Leases

The Company leases its office, laboratory and manufacturing space under non-cancelable operating leases. During August 2012, the Company entered into an Indenture of Lease (the “Amended Lease”), which amended and restated its facility lease. The Amended Lease will terminate on June 30, 2019, but the Company retains an option to renew the Amended Lease with respect to all of the leased space for an additional period of five years. In March 2013, September 2013, February 2015 and July 2015, the Company entered into further facility lease amendments for additional space that are co-terminus with the Amended Lease. In total, the Company leases approximately 167,000 square feet at its corporate headquarters in Cambridge, Massachusetts.

As part of the Amended Lease and subsequent amendments, the landlord agreed to reimburse the Company for a portion of tenant improvements made to the facility. As of December 31, 2016, the Company had received $9.5 million of tenant improvement reimbursements. Tenant improvement reimbursements are recorded within deferred rent and are amortized over the term of the lease as reductions to rent expense.

In May 2016, the Company entered into a sublease agreement (the “Sublease”) whereby a subtenant agreed to lease 8,143 square feet of office and lab space from the Company. The Sublease terminates on December 31, 2017, but may be extended through June 30, 2019 if mutually agreed upon by the Company and the subtenant. Rental income received from the subtenant has been classified by the Company as reduction of rent expense. Total future minimum rental payments to be received by the Company from the subtenant as of December 31, 2016 are $0.6 million.

Total rent expense was $8.6 million, $7.4 million and $5.9 million for the years ended December 31, 2016, 2015 and 2014, respectively.

Future minimum lease payments to be made by the Company under non-cancelable operating leases as of December 31, 2016 are as follows:

Years ended December 31,	(in thousands)
2017	$	8,108
2018		8,102
2019		4,082
Total future minimum lease payments	$	20,292

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2016
Related Party Transactions [Abstract]
Related Party Transactions	19. Related Party Transactions Related parties of the Company held approximately 7% of the outstanding shares of Silver Creek Series A and Series B preferred stock as of both December 31, 2016 and 2015. No shares of Silver Creek Series C preferred stock issued during December 2016 were held by related parties of the Company as of December 31, 2016.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

21. Selected Quarterly Financial Data (Unaudited)

The following table contains quarterly financial information for 2016 and 2015. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period.

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2016
Product revenues, net	$	9,968		$	12,851		$	14,493		$	15,752
License and collaboration revenues		11,313			19,332			12,417			44,057
Other revenues		—			1,498			1,161			1,431
Cost of revenues		711			1,872			1,010			3,319
Research and development expenses		32,882			40,996			32,078			54,961
Selling, general and administrative expenses		17,795			20,680			18,048			24,206
Restructuring expenses		—			—			809			5,047
Net loss		(38,658	)		(50,958	)		(30,275	)		(33,627	)
Net loss attributable to Merrimack Pharmaceuticals, Inc.		(38,473	)		(50,750	)		(30,068	)		(32,449	)
Net loss per share available to common stockholders—basic and diluted		(0.33	)		(0.40	)		(0.23	)		(0.25	)

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2015
Product revenues, net	$	—		$	—		$	—		$	4,328
License and collaboration revenues		14,842			36,558			16,440			17,090
Cost of revenues		—			—			—			46
Research and development expenses		35,679			42,806			37,763			44,740
Selling, general and administrative expenses		9,189			12,315			16,956			19,335
Net loss		(34,432	)		(22,901	)		(42,386	)		(48,068	)
Net loss attributable to Merrimack Pharmaceuticals, Inc.		(34,759	)		(22,778	)		(42,594	)		(47,826	)
Net loss per share available to common stockholders—basic and diluted		(0.32	)		(0.21	)		(0.38	)		(0.41	)

Going Concern	12 Months Ended
Going Concern	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Going Concern	22. Going Concern In accordance with ASC 205-40, Going Concern, the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. The Company has suffered recurring losses from operations, has negative working capital and has cash outflows from operating activities, all of which raise substantial doubt about its ability to continue as a going concern. As of December 31, 2016, the Company had unrestricted cash and cash equivalents of $21.5 million. Upon stockholder approval and the closing of the asset sale with Ipsen outlined more fully in Note 23, “Subsequent Events,” the Company will receive a $575.0 million upfront cash payment from Ipsen (subject to a working capital adjustment as provided in the Asset Sale Agreement). The Company expects to use these proceeds to declare and pay a special cash dividend of at least $200.0 million to stockholders and redeem the $175.0 million outstanding aggregate principal amount of 2022 Notes, which will require an additional make-whole premium payment of approximately $20.1 million. Additionally, if the asset sale is consummated and certain milestones under the Baxalta Agreement are met, the Company currently expects to receive up to an aggregate of $33.0 million in net milestone payments in 2017. The Company believes these potential net cash inflows, along with the completion of the headcount reduction and refocused research and development efforts that were announced in January 2017, will provide financial resources sufficient to fund operations into the second half of 2019. The consummation of the asset sale with Ipsen is contingent upon approval by the Company’s stockholders as well as other customary closing conditions. If the asset sale is not consummated, the Company will not receive the $575.0 million upfront cash payment from Ipsen, and the Company will need to obtain additional funding through public or private debt or equity financings, through existing or new collaboration arrangements, or through divestitures of its assets. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into additional collaborative arrangements. The ability to obtain additional financing is not considered probable at this time and could result in the Company’s inability to meet its obligations as they become due within one year after the date that the consolidated financial statements are issued. Based upon the above evaluation, the Company has concluded that there is substantial doubt as to its ability to continue as a going concern within one year after the date that the consolidated financial statements are issued.

Subsequent Event	12 Months Ended
Subsequent Event	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Events	23. Subsequent Events Asset Sale On January 7, 2017, the Company entered into the Asset Sale Agreement with Ipsen. Pursuant to the Asset Sale Agreement, Ipsen will acquire the Company’s right, title and interest in the non-cash assets, equipment, inventory, contracts and intellectual property primarily related to or used in the Commercial Business. Ipsen will not acquire the Company’s rights to $33.0 million in net milestone payments that may become payable pursuant to the Baxalta Agreement, among other excluded assets. Pursuant to the Asset Sale Agreement, Ipsen will pay the Company $575.0 million in cash (subject to a working capital adjustment as provided in the Asset Sale Agreement) and will assume certain related liabilities. Following the closing of the asset sale, the Company may be entitled to up to $450.0 million of additional payments based on achievement by or on behalf of Ipsen of certain milestone events related to FDA approval of ONIVYDE for certain indications. The consummation of the transaction is subject to customary closing conditions, including, among others: (i) the receipt of the approval of the Company’s stockholders; (ii) the expiration or termination of the required waiting periods under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, which waiting periods expired on February 22, 2017; (iii) the absence of a breach of the Company’s representations and warranties that would cause a material adverse effect on the Commercial Business; (iv) the absence of a business material adverse effect; and (v) the performance of certain covenants in all material respects. The Asset Sale Agreement contains certain termination rights for the Company and Ipsen. Upon termination of the Asset Sale Agreement under specified circumstances, the Company would be required to pay Ipsen a termination fee of $25.0 million, including if the Asset Sale Agreement is terminated in connection with the Company accepting a superior proposal or because the Company’s Board of Directors has changed its recommendation of the sale to its stockholders. The termination fee will also be payable if the Asset Sale Agreement is terminated because the Company’s stockholders did not vote to adopt the Asset Sale Agreement and, prior to such termination, a proposal to acquire at least 50% of the consolidated assets of the Company with respect to the Commercial Business or at least 50% of the Company’s voting securities has been publicly disclosed and the Company enters into a definitive agreement with respect to such proposal within 12 months after such termination, which is subsequently consummated. In addition, the Company would be required to reimburse Ipsen for up to $3.0 million of its out-of-pocket expenses incurred in connection with the transaction and the Asset Sale Agreement if the Asset Sale Agreement is terminated because the Company’s stockholders do not vote to approve it. In addition to the foregoing termination rights, and subject to certain limitations, the Company or Ipsen may terminate the Asset Sale Agreement if the asset sale is not consummated by June 30, 2017. Ipsen has also agreed to sublease 68,409 square feet of the Company’s manufacturing facility at the closing of the asset sale. In addition, at the closing of the asset sale, the Company and Ipsen will enter into an intellectual property license agreement pursuant to which Ipsen will grant the Company an exclusive license with respect to the portion of the transferred patents relating to certain liposomal technology and a non-exclusive license to the remainder of the transferred patents, in both cases for use outside of the field in which the Commercial Business will operate. In turn, the Company will grant Ipsen a non-exclusive license with respect to the remaining patents owned by the Company at the closing for use in the field in which the Commercial Business will operate. January 2017 Corporate Restructuring On January 9, 2017, the Company announced that it will further reduce headcount in connection with the asset sale and the completion of its strategic pipeline review. Upon the closing of the asset sale, the Company will focus its development efforts on its MM-121, MM-141 and MM-310 programs. After the headcount reduction, the Company expects to have approximately 80 employees. The Company’s Board of Directors committed to this course of action on January 6, 2017, subject to the closing of the asset sale, which is contingent upon the closing conditions described above. The reduction in personnel is expected to be complete upon the later of the closing of the asset sale and March 10, 2017. The Company estimates that, if the asset sale closes, it will incur approximately $7.5 million to $8.5 million of restructuring expenses related to one-time employee termination benefits. These one-time employee termination benefits are comprised of severance, benefits and related costs, all of which are expected to result in cash expenditures. The specific timing of the incurrence and payment of these restructuring expenses is dependent upon the timing of the closing of the asset sale. Hiring of Chief Executive Officer On January 16, 2017, the Company announced the hiring of Richard Peters, M.D., Ph.D., as the Company’s new CEO, effective as of February 6, 2017. Dr. Peters was also elected as a member of the Company’s Board of Directors. The Company and Dr. Peters entered into an employment agreement commencing on February 6, 2017 whereby Dr. Peters will receive an annual base salary of $700,000 and is eligible for an annual bonus of up to 65% of his base salary. Dr. Peters also received a one-time signing bonus of $900,000. Subject to the further approval of the Company’s Board of Directors, the Company will also grant Dr. Peters an option to purchase a number of shares of the Company’s common stock equal to the lesser of (i) such number of shares that has a target grant date fair value of $3.5 million and (ii) 2.0 million shares, with an exercise price per share equal to the fair market value of the Company’s common stock on the date of grant. The option will vest over four years at the rate of 25% on February 6, 2018 and the remainder in equal quarterly installments over the following three years. Extension of Credit Facility Availability On February 23, 2017, the Company entered into an amendment to the Credit Agreement with Pharmakon whereby the availability of the credit facility was extended through April 27, 2017. The Company had not borrowed any amounts under the Credit Agreement as of March 1, 2017.

Nature of the Business and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Segment Information

Basis of Presentation and Consolidation

Use of Estimates

Cash, Cash Equivalents and Restricted Cash

Marketable Securities

Inventory

Property and Equipment

Asset Classification		Estimated Useful Life (in years)
Lab equipment		3 - 7
IT equipment		3 - 7
Leaseholds improvements		Lesser of useful life or lease term
Furniture and fixtures		3 - 7

Goodwill and Intangible Assets

Accrued Expenses

•

fees due to contract research organizations in connection with preclinical and toxicology studies and clinical trials;

•

fees paid to investigative sites in connection with clinical trials; and

•

professional service fees.

Non-Controlling Interest

Revenue Recognition

Product Revenues, Net

Product revenue reserves and allowances that reduce gross revenue are categorized as follows:

License and Collaboration Revenues

Other Revenues

Research and Development Expenses

Selling, General and Administrative Expenses

Stock-Based Compensation Expense

Comprehensive Loss

Comprehensive loss consists of net loss and unrealized gains and losses on available-for-sale marketable securities.

Other (Expense) Income, Net

The Company recognized $0.1 million, $0.7 million and $0.4 million in income related to these MLSC tax incentives during the years ended December 31, 2016, 2015 and 2014, respectively.

Income Taxes

Concentration of Credit Risk

	Years Ended December 31,
	2016		2015		2014
Baxalta		60%		93%		10%
Sanofi		—		—		90%
AmerisourceBergen Corporation		15%	<10%			—
McKesson Corporation		16%	<10%			—

	December 31,
	2016		2015
Baxalta		20%		29%
AmerisourceBergen Corporation		25%		29%
McKesson Corporation		32%		25%
Cardinal Health, Inc.		21%		16%

Recent Accounting Pronouncements

•

Nature of the Business and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Schedule of Estimated Useful Lives of Property and Equipment Including Leasehold Improvements

Asset Classification		Estimated Useful Life (in years)
Lab equipment		3 - 7
IT equipment		3 - 7
Leaseholds improvements		Lesser of useful life or lease term
Furniture and fixtures		3 - 7

Schedules of Concentration of Risk by Risk Factor

	Years Ended December 31,
	2016		2015		2014
Baxalta		60%		93%		10%
Sanofi		—		—		90%
AmerisourceBergen Corporation		15%	<10%			—
McKesson Corporation		16%	<10%			—

	December 31,
	2016		2015
Baxalta		20%		29%
AmerisourceBergen Corporation		25%		29%
McKesson Corporation		32%		25%
Cardinal Health, Inc.		21%		16%

Net Loss Per Common Share (Tables)

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Schedule of Securities Excluded from Computation of Diluted Loss Per Share

Securities excluded from the calculation of diluted loss per share are shown in the chart below:

	Years Ended December 31,
(in thousands)	2016		2015		2014
Common stock warrants		—		—		2,381
Outstanding options to purchase common stock		19,025		19,211		19,567
Conversion of the Convertible Notes		12,158		25,000		25,000

License and Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2016

Baxalta [Member]

Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements

During the years ended December 31, 2016, 2015 and 2014, the Company recognized license and collaboration revenues based on the following components of the Baxalta Agreement:

	Years Ended December 31,
(in thousands)	2016		2015		2014
Proportional performance revenue recognition model	$	47,119	$	64,930	$	10,460
Substantive milestones		40,000		20,000		—
Total	$	87,119	$	84,930	$	10,460

During the year ended December 31, 2016, the Company also recognized royalty revenues of $0.2 million related to the Baxalta Agreement.

As of December 31, 2016 and 2015, the Company maintained the following assets and liabilities related to the Baxalta Agreement:

	December 31,
(in thousands)	2016		2015
Accounts receivable, billed	$	860	$	1,336
Accounts receivable, unbilled		581		626
Deferred revenues		56,779		97,365

Sanofi [Member]

Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements

(in thousands)	Year Ended December 31, 2014
Upfront payment	$	39,306
Milestone payment		16,377
Development services		18,904
Manufacturing services and other		17,709
Total	$	92,296

Product Revenue Reserves and Allowances (Tables)

12 Months Ended

Dec. 31, 2016

Product Revenue Reserves And Allowances [Abstract]

Summary of Product Revenue Reserve and Allowance Categories

The following table summarizes activity in each of the product revenue reserve and allowance categories for the year ended December 31, 2016:

(in thousands)	Trade Allowances			Rebates and Chargeback Discounts			Product Returns			Other Incentives			Total
Balance at December 31, 2015	$	138		$	362		$	32		$	8		$	540
Provisions related to sales in the current year		1,900			5,928			397			5			8,230
Adjustments related to sales in the prior year		—			(213	)		—			—			(213	)
Credits and payments made		(1,507	)		(5,077	)		(26	)		(7	)		(6,617	)
Balance at December 31, 2016	$	531		$	1,000		$	403		$	6		$	1,940

Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2016

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis

	December 31, 2016
(in thousands)	Level 1		Level 2		Level 3
Assets:
Money market funds	$	12,373	$	—	$	—
Totals	$	12,373	$	—	$	—

Liabilities:
Silver Creek warrant liability	$	—	$	—	$	1,499
Totals	$	—	$	—	$	1,499

	December 31, 2015
(in thousands)	Level 1		Level 2		Level 3
Assets:
Money market funds	$	704	$	—	$	—
Totals	$	704	$	—	$	—

Inventory (Tables)

12 Months Ended

Dec. 31, 2016

Inventory Disclosure [Abstract]

Schedule of Inventory

Inventory as of December 31, 2016 and 2015 consisted of the following:

	December 31,
(in thousands)	2016		2015
Raw materials	$	4,483	$	900
Work in process		8,651		2,743
Finished goods		1,420		74
Total inventory	$	14,554	$	3,717

Goodwill and Intangible Assets, Net (Tables)

12 Months Ended

Dec. 31, 2016

Goodwill And Intangible Assets Disclosure [Abstract]

Schedule of Goodwill and Intangible Assets

Goodwill and intangible assets as of December 31, 2016 and 2015 consisted of the following:

	December 31, 2016
(in thousands)	Gross Carrying Value		Accumulated Amortization			Net Carrying Value
Nano-carrier technology intangible asset	$	3,200	$	(2,315	)	$	885
ONIVYDE intangible asset		3,400		(308	)		3,092
Goodwill		3,605		—			3,605
Totals	$	10,205	$	(2,623	)	$	7,582

	December 31, 2015
(in thousands)	Gross Carrying Value		Accumulated Amortization			Net Carrying Value
Nano-carrier technology intangible asset	$	3,200	$	(1,995	)	$	1,205
ONIVYDE intangible asset		3,400		(50	)		3,350
IPR&D		2,800		—			2,800
Goodwill		3,605		—			3,605
Totals	$	13,005	$	(2,045	)	$	10,960

Schedule of Expected Future Amortization Expense for Intangible Assets for the Next Five-Year Period

Future amortization expense for the next five-year period is expected to be as follows:

Years Ended December 31,	(in thousands)
2017	$	578
2018		578
2019		503
2020		258
2021		258

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2016

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net as of December 31, 2016 and 2015 consisted of the following:

	December 31,
(in thousands)	2016			2015
Lab equipment	$	20,752		$	19,305
IT equipment		8,601			7,742
Leasehold improvements		21,153			21,026
Furniture and fixtures		959			910
Construction in process		515			2,243
Total property and equipment, gross		51,980			51,226
Less: Accumulated depreciation		(36,215	)		(29,311	)
Total property and equipment, net	$	15,765		$	21,915

Accounts Payable, Accrued Expenses and Other (Tables)

12 Months Ended

Dec. 31, 2016

Payables And Accruals [Abstract]

Schedule of Accounts Payable, Accrued Expenses and Other

Accounts payable, accrued expenses and other as of December 31, 2016 and 2015 consisted of the following:

	December 31,
(in thousands)	2016		2015
Accounts payable	$	3,384	$	5,049
Accrued goods and services		15,760		14,295
Accrued clinical trial costs		11,260		12,764
Accrued drug purchase costs		910		7,460
Accrued payroll and related benefits		9,150		9,009
Accrued restructuring expenses		774		—
Accrued asset sale transaction costs		3,724		—
Accrued interest		2,100		3,041
Accrued dividends payable		19		19
Silver Creek warrant liability		1,499		—
Deferred tax incentives		1,402		445
Total accounts payable, accrued expenses and other	$	49,982	$	52,082

Borrowings (Tables)

12 Months Ended

Dec. 31, 2016

Debt Disclosure [Abstract]

Schedule of Future Minimum Payments under the Loans Payable

Future minimum payments under outstanding borrowings as of December 31, 2016 are as follows:

(in thousands)	Convertible Notes			2022 Notes
2017	$	2,736		$	20,125
2018		2,736			20,125
2019		2,736			62,617
2020		63,527			57,586
2021 and thereafter		—			100,078
Total		71,735			260,531
Less interest		(10,943	)		(85,531	)
Less unamortized discount		(13,842	)		(5,089	)
Less current portion		—			—
Long-term debt	$	46,950		$	169,911

Restructuring Activities (Tables)

12 Months Ended

Dec. 31, 2016

Restructuring And Related Activities [Abstract]

Summary of Charges Related to Restructuring Activities

The following table summarizes the charges related to the restructuring activities as of December 31, 2016:

(in thousands)

Expenses

Less: Payments

Less: Non-Cash Expenses

Accrued Restructuring Expenses at

December 31, 2016

Severance, benefits and related costs due

to workforce reduction

5,856

(3,711

)

(1,371

)

774

Totals

5,856

(3,711

)

(1,371

)

774

Common Stock Warrants (Tables)

12 Months Ended

Dec. 31, 2016

Text Block [Abstract]

Schedule of Common Stock Warrant Activity of the Company

The following is a description of the common stock warrant activity of the Company:

(in thousands, except per share amounts)	Warrants for the Purchase of Common Stock			Weighted Average Exercise Price
Balance at December 31, 2013		2,777		$	3.05
Exercised		(396	)	$	3.38
Balance at December 31, 2014		2,381		$	3.00
Exercised		(2,355	)	$	3.00
Cancelled		(26	)	$	3.00
Balance at December 31, 2015		—		$	—

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees

The fair value of stock options granted to employees during the years ended December 31, 2016, 2015 and 2014 was estimated at the date of grant using the following assumptions:

	Years Ended December 31,
	2016	2015	2014
Risk-free interest rate	1.1 – 2.0%	1.5 – 1.8%	1.6 – 2.0%
Expected dividend yield	0%	0%	0%
Expected term	5.0 – 5.8 years	5.0 – 5.9 years	5.0 – 5.9 years
Expected volatility	67 – 69%	66 – 67%	64 – 72%

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense during the years ended December 31, 2016, 2015 and 2014 as follows:

	Years Ended December 31,
(in thousands)	2016			2015		2014
Employee awards:
Research and development expense	$	6,503		$	8,271	$	6,864
Selling, general and administrative expense		7,331			7,022		6,065
Restructuring expense		1,371			—		—
Stock-based compensation expense for employee awards		15,205			15,293		12,929
Stock-based compensation expense for non-employee awards		1			58		268
Less: stock-based compensation expense capitalized to inventory		(341	)		—		—
Total stock-based compensation expense	$	14,865		$	15,351	$	13,197

Summary of Stock Option Activity

The following table summarizes stock option activity during the year ended December 31, 2016:

(in thousands, except per share amounts)	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2015		19,211		$	5.72		6.24	$	47,963
Granted		4,258		$	5.57
Exercised		(1,958	)	$	3.29
Forfeited		(2,487	)	$	7.04
Outstanding at December 31, 2016		19,024		$	5.77		5.97	$	7,564
Vested and expected to vest at December 31, 2016		18,794		$	5.76		5.93	$	7,564
Exercisable at December 31, 2016		14,968		$	5.49		5.24	$	7,564

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate

A reconciliation of the Company’s effective tax rate to the statutory federal income tax rate is as follows:

	Years Ended December 31,
	2016			2015			2014
Federal income tax at statutory federal rate		35.0	%		35.0	%		35.0	%
State taxes		0.7			1.0			3.1
Permanent differences		(11.6	)		(6.4	)		(9.1	)
Stock-based compensation		(2.2	)		(1.3	)		(1.7	)
Tax credits		28.0			21.3			30.5
Foreign rate differential		—			—			(2.3	)
Change in deferred state tax rate		(0.3	)		(2.3	)		—
Other		4.5			(0.5	)		4.5
Change in valuation allowance		(54.1	)		(46.8	)		(60.0	)
Total		—	%		—	%		—	%

Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets

Temporary differences that give rise to significant net deferred tax assets as of December 31, 2016 and 2015 are as follows:

	December 31,
(in thousands)	2016			2015
Deferred tax assets
Net operating losses	$	194,027		$	182,992
Capitalized research and development expenses		15,854			21,444
Credit carryforwards		144,823			93,113
Depreciation		2,557			2,128
Deferred compensation		12,463			11,664
Accrued expenses		3,601			1,807
Deferred revenue		21,935			10,999
Other temporary differences		25,276			17,235
Total gross deferred tax assets		420,536			341,382
Valuation allowance		(414,558	)		(326,577	)
Net deferred tax assets		5,978			14,805
Deferred tax liabilities
Intangible assets		(1,428	)		(2,667	)
Debt discount		(4,550	)		(12,138	)
Net deferred taxes	$	—		$	—

Schedule of Changes in the Valuation Allowance

The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2016, 2015 and 2014 was as follows:

(in thousands)	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
December 31, 2014	$	207,304	$	50,185	$	—	$	257,489
December 31, 2015		257,489		69,088		—		326,577
December 31, 2016		326,577		87,981		—		414,558

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2016

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases

Future minimum lease payments to be made by the Company under non-cancelable operating leases as of December 31, 2016 are as follows:

Years ended December 31,	(in thousands)
2017	$	8,108
2018		8,102
2019		4,082
Total future minimum lease payments	$	20,292

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2016
Product revenues, net	$	9,968		$	12,851		$	14,493		$	15,752
License and collaboration revenues		11,313			19,332			12,417			44,057
Other revenues		—			1,498			1,161			1,431
Cost of revenues		711			1,872			1,010			3,319
Research and development expenses		32,882			40,996			32,078			54,961
Selling, general and administrative expenses		17,795			20,680			18,048			24,206
Restructuring expenses		—			—			809			5,047
Net loss		(38,658	)		(50,958	)		(30,275	)		(33,627	)
Net loss attributable to Merrimack Pharmaceuticals, Inc.		(38,473	)		(50,750	)		(30,068	)		(32,449	)
Net loss per share available to common stockholders—basic and diluted		(0.33	)		(0.40	)		(0.23	)		(0.25	)

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2015
Product revenues, net	$	—		$	—		$	—		$	4,328
License and collaboration revenues		14,842			36,558			16,440			17,090
Cost of revenues		—			—			—			46
Research and development expenses		35,679			42,806			37,763			44,740
Selling, general and administrative expenses		9,189			12,315			16,956			19,335
Net loss		(34,432	)		(22,901	)		(42,386	)		(48,068	)
Net loss attributable to Merrimack Pharmaceuticals, Inc.		(34,759	)		(22,778	)		(42,594	)		(47,826	)
Net loss per share available to common stockholders—basic and diluted		(0.32	)		(0.21	)		(0.38	)		(0.41	)

Nature of the Business and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) Segment Region	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment	1
Number of geographic regions \| Region	1
Original maturities	Three months or less
Restricted cash	$ 0.8	$ 0.7
Advertising expenses	$ 4.5	1.0
Performance period	5 years
Tax incentive awarded	$ 3.8
State research and development tax credits monetized	3.4
Amount of tax incentives required to repay	1.3
Amount of benefit recognized	$ 0.1	$ 0.7	$ 0.4
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected remaining maturities period of marketable securities classified as available-for-sale	3 months

Nature of the Business and Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment Including Leasehold Improvements (Detail)	12 Months Ended
	Dec. 31, 2016
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	Lesser of useful life or lease term
Minimum [Member] \| Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] \| IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] \| Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Maximum [Member] \| Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Maximum [Member] \| IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Maximum [Member] \| Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years

Nature of the Business and Summary of Significant Accounting Policies - Schedules of Concentration of Risk by Risk Factor - Gross Sales Revenue (Detail) - Sales Revenue, Net [Member] - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Baxalta [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue	60.00%	93.00%	10.00%
Sanofi [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue			90.00%
Amerisource Bergen Corporation [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue	15.00%
Amerisource Bergen Corporation [Member] \| Maximum [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue		10.00%
McKesson Corporation [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue	16.00%
McKesson Corporation [Member] \| Maximum [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue		10.00%

Nature of the Business and Summary of Significant Accounting Policies - Schedules of Concentration of Risk by Risk Factor - Gross Accounts Receivable (Detail) - Accounts Receivable [Member] - Credit Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Baxalta [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable	20.00%	29.00%
Amerisource Bergen Corporation [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable	25.00%	29.00%
McKesson Corporation [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable	32.00%	25.00%
Cardinal Health Inc [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable	21.00%	16.00%

Consolidated Subsidiaries - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Aug. 31, 2016	May 31, 2016	Dec. 31, 2013
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Preferred stock value, per share	$ 0.01	$ 0.01	$ 0.01
Preferred stock issued	0	0	0
Net cash proceeds from stock issuance		$ 3,361	$ 2,083
Total assets of consolidated subsidiaries	$ 81,483	81,483	234,880
Total liabilities of consolidated subsidiaries	334,142	334,142	418,569
Cash and cash equivalents	21,524	21,524	185,606	$ 35,688			$ 65,086
Series B Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Increase (decrease) in non-controlling interest			1,188
Series C Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Increase (decrease) in non-controlling interest		$ 2,689
Silver Creek [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Acquisition date		Aug. 20, 2010
Increase (decrease) in non-controlling interest				400
Total assets of consolidated subsidiaries	2,000	$ 2,000	800
Total liabilities of consolidated subsidiaries	2,000	2,000	200
Cash and cash equivalents	$ 1,900	$ 1,900	700
Silver Creek [Member] \| Convertible Promissory Notes [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Aggregate principal amount					$ 200	$ 1,000
Silver Creek [Member] \| Silver Creek Convertible Note [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Aggregate principal amount				$ 1,000
Silver Creek [Member] \| Series A Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Preferred stock value, per share				$ 1.00
Silver Creek [Member] \| Series B Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Increase (decrease) in non-controlling interest			$ 900
Preferred stock issued			1,600
Preferred stock price per share			$ 1.35
Net cash proceeds from stock issuance			$ 2,100
Silver Creek [Member] \| Series C Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Preferred stock value, per share	$ 1.50	$ 1.50
Increase (decrease) in non-controlling interest		$ (800)
Preferred stock issued	1,500	1,500
Preferred stock price per share	$ 1.50	$ 1.50
Net cash proceeds from stock issuance	$ 2,100
Warrants issued to purchase preferred stock, shares	1,900	1,900
Silver Creek [Member] \| Series A, Series B and Series C Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ownership interest (as a percent)	50.00%	50.00%	56.00%
Non-controlling interest	$ (1,500)	$ (1,500)	$ 200

Net Loss Per Common Share - Additional Information (Detail) - Convertible Notes [Member] - USD ($) $ in Millions	Dec. 31, 2016	Jul. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Aggregate principal amount		$ 125.0
Interest rate (as a percent)		4.50%
Aggregate principal amount of outstanding debt	$ 60.8

Net Loss Per Common Share - Schedule of Securities Excluded from Computation of Diluted Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted loss per share			2,381
Outstanding Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted loss per share	19,025	19,211	19,567
Conversion of the Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted loss per share	12,158	25,000	25,000

License and Collaboration Agreements - Additional Information (Detail) - USD ($)					1 Months Ended								3 Months Ended								12 Months Ended				27 Months Ended
	Sep. 23, 2014	Nov. 25, 2013	May 05, 2011	Nov. 10, 2009	Dec. 31, 2016	Oct. 31, 2016	Jun. 30, 2016	Oct. 31, 2015	Aug. 31, 2015	Jul. 31, 2015	Jan. 31, 2015	Sep. 30, 2014	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenues, current					$ 36,226,000								$ 36,226,000				$ 50,137,000				$ 36,226,000	$ 50,137,000			$ 36,226,000
Other revenues													1,431,000	$ 1,161,000	$ 1,498,000						$ 4,090,000
Agreement termination scheduled date																					Dec. 17, 2014
License and collaboration revenues													44,057,000	12,417,000	19,332,000	$ 11,313,000	17,090,000	$ 16,440,000	$ 36,558,000	$ 14,842,000	$ 87,119,000	84,930,000	$ 102,756,000
Assets maintained related to Sanofi Agreement					81,483,000								81,483,000				234,880,000				81,483,000	234,880,000			81,483,000
Liabilities maintained related to Sanofi Agreement					334,142,000								334,142,000				418,569,000				334,142,000	418,569,000			334,142,000
Research and development expenses													54,961,000	$ 32,078,000	$ 40,996,000	$ 32,882,000	44,740,000	$ 37,763,000	42,806,000	$ 35,679,000	160,917,000	160,988,000	138,495,000
Deferred Revenue, Noncurrent					25,673,000								25,673,000				51,197,000				$ 25,673,000	51,197,000			25,673,000
Baxalta [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront license fee received												$ 100,000,000
Baxalta [Member] \| Regulatory Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone license fee received																									60,000,000
Maximum amount of milestone payments that can be received	$ 520,000,000
Baxalta [Member] \| Research and Development Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone license fee received																									62,500,000
Maximum amount of milestone payments that can be received	100,000,000
Baxalta [Member] \| Sales Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received	250,000,000
Baxalta [Member] \| Clinical Trials in Pancreatic Cancer [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement costs	98,800,000
Baxalta [Member] \| License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty for improved products																					The Company is also entitled to tiered, escalating royalties ranging from sub-teen double digits to low twenties percentages of net sales of ONIVYDE in the Licensed Territory.
Notice period of termination																					180 days
Revenue recognized related to a substantive milestone payment						$ 30,000,000	$ 10,000,000	$ 47,500,000	$ 15,000,000	$ 20,000,000
Royalty revenue																					$ 200,000
Deferred revenues					56,779,000								56,779,000				97,365,000				56,779,000	97,365,000			56,779,000
Deferred revenues, current					36,200,000								36,200,000								36,200,000				36,200,000
License and collaboration revenues																					87,119,000	84,930,000	10,460,000
Baxalta [Member] \| Non-Substantive Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone license fee received																									62,500,000
Milestone license fee	90,000,000
Baxalta [Member] \| Substantive Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone license fee received																									60,000,000
Milestone license fee	$ 530,000,000
Baxalta [Member] \| Commercial Supply Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Other revenues																					3,600,000
Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront license fee received				$ 60,000,000
Milestone license fee received																					25,000,000
Expected development period from the effective date of agreement				12 years
License and collaboration revenues																					0	0
Assets maintained related to Sanofi Agreement					0								0				0				0	0			0
Liabilities maintained related to Sanofi Agreement					0								0				0				0	0			0
Sanofi [Member] \| License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and collaboration revenues																							92,296,000
Recognized revenue related to excess spending																							5,800,000
Spending in excess of budget																								$ 10,100,000
PharmaEngine [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront license fees paid			$ 10,000,000
Milestone payment					25,500,000		$ 10,000,000			$ 11,000,000		$ 7,000,000							$ 5,000,000
Royalty expense																					100,000
PharmaEngine [Member] \| Sales Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payment obligation			130,000,000
PharmaEngine [Member] \| Development and Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payment obligation			$ 80,000,000
PharmaEngine [Member] \| License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expenses																					35,600,000	11,400,000	$ 12,600,000
PharmaEngine [Member] \| Commercial Supply Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Other revenues																					$ 300,000	0
Actavis [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Notice period of termination																					90 days
Maximum amount of milestone and development payments that can be received		$ 15,100,000
Collaborative arrangement gross payments received																					$ 4,900,000
Aggregate milestone payments eligible to receive, decrease											$ 400,000
Percentage of net profits on global sales of product																					The Company will also receive a mid-twenties percentage of net profits on global sales of the Initial Product and any additional products.
Milestones achieved						$ 1,100,000
Agreement expiration term respect to each product																					10 years
Additional renewal term																					2 years
Deferred Revenue, Noncurrent					$ 5,100,000								$ 5,100,000				$ 4,000,000				$ 5,100,000	$ 4,000,000			$ 5,100,000
Expected revenue recognition period begins after first sale of applicable product																					10 years

License and Collaboration Agreements - Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total	$ 44,057,000	$ 12,417,000	$ 19,332,000	$ 11,313,000	$ 17,090,000	$ 16,440,000	$ 36,558,000	$ 14,842,000	$ 87,119,000	$ 84,930,000	$ 102,756,000
Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total									0	0
License and Collaboration Agreements [Member] \| Baxalta [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proportional performance revenue recognition model									47,119,000	64,930,000	10,460,000
Substantive milestones									40,000,000	20,000,000
Total									87,119,000	84,930,000	10,460,000
Accounts receivable, billed	860,000				1,336,000				860,000	1,336,000
Accounts receivable, unbilled	581,000				626,000				581,000	626,000
Deferred revenues	$ 56,779,000				$ 97,365,000				$ 56,779,000	$ 97,365,000
License and Collaboration Agreements [Member] \| Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total											92,296,000
Upfront payment											39,306,000
Milestone payment											16,377,000
Development services											18,904,000
Manufacturing services and other											$ 17,709,000

Product Revenue Reserves and Allowances - Summary of Product Revenue Reserve and Allowance Categories (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	$ 540
Provisions related to sales in the current year	8,230
Adjustments related to sales in the prior year	(213)
Credits and payments made	(6,617)
Ending balance	1,940
Trade Allowances [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	138
Provisions related to sales in the current year	1,900
Credits and payments made	(1,507)
Ending balance	531
Rebates and Chargeback Discounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	362
Provisions related to sales in the current year	5,928
Adjustments related to sales in the prior year	(213)
Credits and payments made	(5,077)
Ending balance	1,000
Product Returns [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	32
Provisions related to sales in the current year	397
Credits and payments made	(26)
Ending balance	403
Other Incentives [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	8
Provisions related to sales in the current year	5
Credits and payments made	(7)
Ending balance	$ 6

Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - Recurring Basis [Member] - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities		$ 0
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	$ 12,373,000	704,000
Level 1 [Member] \| Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	12,373,000	$ 704,000
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	1,499,000
Level 3 [Member] \| Silver Creek [Member] \| Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	$ 1,499,000

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 22, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Transfers between fair value measurement levels	$ 0	$ 0
Non-recurring fair value measurements		0
Senior Convertible Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Aggregate principal amount of outstanding debt	47,000,000
Senior Convertible Notes [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of debt	57,500,000
2022 Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of debt	167,000,000
Aggregate principal amount of outstanding debt	169,900,000
Aggregate principal amount of loan			$ 175,000,000
Interest rate (as a percent)			11.50%
IPR&D [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of assets	$ 0
Recurring Basis [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value		$ 0
Silver Creek [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Risk-free interest rate	2.30%
Expected dividend yield	0.00%
Expected volatility	61.70%
Expected term	6 years 10 months 24 days
Silver Creek [Member] \| Series C Preferred Stock [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Warrants issued to purchase preferred stock, shares	1.9
Warrants to purchase preferred stock, value	$ 1,500,000

Marketable Securities - Additional Information (Detail)	12 Months Ended
Marketable Securities - Additional Information (Detail)	Dec. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Amortized Cost And Fair Value Debt Securities [Abstract]
Number of securities held in unrealized loss position	0
Number of securities with other-than-temporary impairment	0
Realized gains (losses) on sale of available-for-sale securities \| $	$ 0	$ 0	$ 0

Inventory - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
Raw materials	$ 4,483	$ 900
Work in process	8,651	2,743
Finished goods	1,420	74
Total inventory	$ 14,554	$ 3,717

Goodwill and Intangible Assets, Net - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Impairment charge			$ 2,800,000
Impairment charges related to goodwill			0	$ 0	$ 0
Impairment charges related to definite-lived intangible assets			0	0	0
Amortization expenses of intangible assets			$ 600,000	$ 400,000	$ 300,000
Weighted-average remaining amortization period of intangible assets			10 years
Core Nano Carrier Technology [Member]
Business Acquisition [Line Items]
Amortization period of intangible assets			10 years
IPR&D [Member]
Business Acquisition [Line Items]
Impairment charge	$ 2,800,000
Other In-process Research and Development Program [Member]
Business Acquisition [Line Items]
Impairment charge		$ 800,000
Hermes BioSciences, Inc. [Member]
Business Acquisition [Line Items]
Acquired IPR&D assets recognized in a business combination			$ 7,000,000
Acquisition date			Oct. 06, 2009
Acquired goodwill recognized in a business combination			$ 3,600,000
Hermes BioSciences, Inc. [Member] \| Core Nano Carrier Technology [Member]
Business Acquisition [Line Items]
Acquired intangible assets			3,200,000
Hermes BioSciences, Inc. [Member] \| Antibody Targeted Nanotherapeutic Program with Chemotherapy Drug [Member]
Business Acquisition [Line Items]
Acquired IPR&D assets recognized in a business combination			2,800,000
Hermes BioSciences, Inc. [Member] \| Nanotherapeutic Program with Chemotherapy Drug [Member]
Business Acquisition [Line Items]
Acquired IPR&D assets recognized in a business combination			3,400,000
Hermes BioSciences, Inc. [Member] \| Other In-process Research and Development Program [Member]
Business Acquisition [Line Items]
Acquired IPR&D assets recognized in a business combination			$ 800,000

Goodwill and Intangible Assets, Net - Schedule of Goodwill and Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Intangible Assets By Major Class [Line Items]
Intangible assets, Accumulated Amortization	$ (2,623)	$ (2,045)
Goodwill	3,605	3,605
Goodwill and Intangible assets, Gross Carrying Value	10,205	13,005
Goodwill and Intangible assets, Net Carrying Value	7,582	10,960
IPR&D [Member]
Intangible Assets By Major Class [Line Items]
Indefinite-lived intangible asset		2,800
Nano Carrier Technology [Member]
Intangible Assets By Major Class [Line Items]
Intangible assets, Gross Carrying Value	3,200	3,200
Intangible assets, Accumulated Amortization	(2,315)	(1,995)
Intangible assets, Net Carrying Value	885	1,205
ONIVYDE [Member]
Intangible Assets By Major Class [Line Items]
Intangible assets, Gross Carrying Value	3,400	3,400
Intangible assets, Accumulated Amortization	(308)	(50)
Intangible assets, Net Carrying Value	$ 3,092	$ 3,350

Goodwill and Intangible Assets, Net - Schedule of Expected Future Amortization Expense for Intangible Assets for the Next Five-Year Period (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
2017	$ 578
2018	578
2019	503
2020	258
2021	$ 258

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 51,980	$ 51,226
Less: Accumulated depreciation	(36,215)	(29,311)
Total property and equipment, net	15,765	21,915
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	20,752	19,305
IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	8,601	7,742
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	21,153	21,026
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	959	910
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 515	$ 2,243

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant and Equipment Useful Life and Values [Abstract]
Depreciation expense	$ 7,300	$ 5,500	$ 4,200
Charge related to disposal of property and equipment	$ 493	$ 4

Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts Payable And Accrued Liabilities [Line Items]
Accounts payable	$ 3,384	$ 5,049
Accrued goods and services	15,760	14,295
Accrued clinical trial costs	11,260	12,764
Accrued drug purchase costs	910	7,460
Accrued payroll and related benefits	9,150	9,009
Accrued restructuring expenses	774
Accrued asset sale transaction costs	3,724
Accrued interest	2,100	3,041
Accrued dividends payable	19	19
Deferred tax incentives	1,402	445
Total accounts payable, accrued expenses and other	49,982	$ 52,082
Silver Creek [Member]
Accounts Payable And Accrued Liabilities [Line Items]
Warrant liability	$ 1,499

Borrowings - 2022 Notes - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 22, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Debt maturity date		Jul. 15, 2020
Interest expense		$ 43,645,000	$ 19,232,000	$ 18,230,000
Change of Control Event [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	101.00%
Asset Sale Event [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	100.00%
2022 Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 175,000,000
Interest rate (as a percent)	11.50%
Net proceeds from the debt issuance	$ 168,500,000
Debt issuance costs	900,000
Semi-annual installments of principal	$ 21,875,000
Debt maturity date	Dec. 15, 2022
Effective interest rate		12.32%
Interest expense		$ 20,900,000	$ 500,000
2022 Notes [Member] \| Conversion Terms, Fundamental Changes [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest		100.00%

Borrowings - Convertible Notes - Additional Information (Detail)				1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 18, 2016 shares	Apr. 13, 2016 USD ($) shares	Jul. 31, 2013 USD ($) $ / shares	Jul. 31, 2013 USD ($) $ / shares	Jun. 30, 2016 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Principal amount of convertible notes due 2020 converted into shares of common stock						$ 64,209,000
Common stock, shares issued \| shares						130,197,000	115,871,000
Loss on extinguishment of debt						$ 14,566,000
Debt maturity date						Jul. 15, 2020
Interest expense						$ 43,645,000	$ 19,232,000	$ 18,230,000
Convertible Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount			$ 125,000,000	$ 125,000,000
Net proceeds from the debt issuance				$ 120,600,000
Interest rate (as a percent)			4.50%	4.50%
Embedded conversion option			$ 53,800,000	$ 53,800,000
Underwriting discounts and commissions and offering expenses			4,400,000
Principal amount of convertible notes due 2020 converted into shares of common stock		$ 64,200,000
Conversion ratio, principal amount		$ 1,000	$ 1,000	$ 1,000
Conversion rate of common stock shares per $1,000 principal amount	136		160
Common stock, shares issued \| shares	8,732,152	3,635,511			12,367,663
Value of additional shares issued for conversion		$ 27,700,000
Trading period		10 days
Increase to additional paid in capital pursuant to conversion					$ 101,000,000
Loss on extinguishment of debt					14,600,000
Reduction in additional paid-in capital attributable to embedded conversion option					$ 39,800,000
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible			30 days
Convertibility of debt, closing price of stock test, percentage of stock price to conversion price for the notes that must be exceeded			130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period			5 days
Number of consecutive trading days before five consecutive business days during the note measurement period			5 days
Initial conversion price of shares (in dollars per share) \| $ / shares			$ 6.25	$ 6.25
Minimum percentage of aggregate principal amount held by bondholders to declare notes due and payable			25.00%
Percentage of principal amount due and payable upon event of default			100.00%
Interest expense						22,700,000	$ 13,700,000	$ 13,700,000
Convertible Notes [Member] \| Conversion Terms, Fundamental Changes [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest			100.00%
Convertible Notes [Member] \| Conversion Terms, Event of Default [Member]
Debt Instrument [Line Items]
Percentage of principal amount due and payable upon event of default arising out of certain bankruptcy events			100.00%
Convertible Notes [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible			20 days
Convertible Notes [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Convertibility of debt, trading price of debt test, percentage of closing price of stock used in calculation			98.00%
Convertible Notes [Member] \| Transaction Costs Incurred With Third Parties [Member]
Debt Instrument [Line Items]
Reduction in additional paid-in capital						200,000
Convertible Notes [Member] \| Interest Expense [Member] \| Transaction Costs Incurred With Third Parties [Member]
Debt Instrument [Line Items]
Transaction costs related to conversion of convertible notes due 2020 incurred and paid						$ 200,000

Borrowings - Loan Agreement - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 25, 2015	Nov. 06, 2014	Dec. 22, 2015	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Nov. 30, 2012
Schedule Of Debt Instruments [Line Items]
Extension period for interest-only payment		4 months
Repayment of notes				$ 40,000,000
Interest expense					$ 43,645,000	$ 19,232,000	$ 18,230,000
2022 Notes [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount			$ 175,000,000
Unamortized debt issuance costs					5,089,000
Debt issuance costs			$ 900,000
Interest expense					20,900,000	500,000
2022 Notes [Member] \| Modified Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Unamortized debt issuance costs				$ 300,000		300,000
Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Discount on loan recorded as a non-current liability to be paid upon full repayment or maturity of the loans					1,200,000
Hercules [Member]
Schedule Of Debt Instruments [Line Items]
Initial debt discount					1,600,000
Interest expense					$ 0	5,400,000	$ 4,700,000
Hercules [Member] \| 2022 Notes [Member] \| Modified Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Debt issuance costs						$ 900,000
Hercules [Member] \| Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount	$ 40,000,000							$ 40,000,000
Outstanding principal balance repayment start date	Jun. 01, 2016
Outstanding principal balance repayment end date	Nov. 01, 2018
Extended maturity period on principal payment	6 months

Borrowings - Credit Facility - Additional Information (Detail) - BioPharma Credit Investments IV Sub, LP (“Pharmakon”) [Member] - Credit Agreement [Member] - USD ($)			12 Months Ended
	Feb. 23, 2017	Nov. 08, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Credit facility principal amount, minimum amount		$ 15,000,000
Credit facility principal amount, maximum amount		$ 25,000,000
Credit facility, expiration date		Mar. 15, 2017
Credit facility, annual interest rate		11.50%
Credit facility, optional future financing, description			In addition, the Credit Agreement grants Pharmakon an option during the two years following funding of the credit facility to participate in a future financing at an amount up to the lesser of 25% of the total amount financed or $50.0 million.
Credit facility, future financing, expiration period		2 years
Maximum percentage of participation in future financing		25.00%
Maximum dollar amount of participation in future financing		$ 50,000,000
Credit facility, amounts borrowed			$ 0
Subsequent Event [Member]
Debt Instrument [Line Items]
Credit facility, expiration date	Apr. 27, 2017

Borrowings - Silver Creek Convertible Notes - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands	1 Months Ended			12 Months Ended
	Dec. 31, 2016	May 31, 2016	Dec. 31, 2012	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Aug. 31, 2016
Debt Instrument [Line Items]
Preferred stock issued	0			0	0
Proceeds from sale of preferred stock				$ 3,361,000	$ 2,083,000
Silver Creek [Member] \| Convertible Notes [Member]
Debt Instrument [Line Items]
Interest rate (as a percent)		6.00%
Aggregate principal amount		$ 1,000,000						$ 200,000
Debt instrument conversion price per share		$ 1.60
Minimum gross proceeds for next equity financing conversion		$ 4,000,000
Silver Creek [Member] \| Series B Preferred Stock [Member]
Debt Instrument [Line Items]
Preferred stock issued					1,600
Preferred stock price per share					$ 1.35
Proceeds from sale of preferred stock					$ 2,100,000
Silver Creek [Member] \| Series B Preferred Stock [Member] \| Convertible Notes [Member]
Debt Instrument [Line Items]
Debt instrument conversion price per share	$ 1.35			$ 1.35
Silver Creek [Member] \| Silver Creek Series C Preferred Stock [Member]
Debt Instrument [Line Items]
Preferred stock issued	1,500			1,500
Preferred stock price per share	$ 1.50			$ 1.50
Warrants to purchase	1,900			1,900
Proceeds from sale of preferred stock	$ 2,100,000
Silver Creek [Member] \| Silver Creek Series C Preferred Stock [Member] \| Milestone Event 1 [Member]
Debt Instrument [Line Items]
Number of warrants exercisable	1,200			1,200
Description of milestone event achievement				Milestone Event 1 is defined as the date that is seven business days following the acceptance by the FDA of Silver Creek’s filing of an Investigational New Drug application (“IND”), or 30 business days after the IND is filed without FDA rejection of the application.
Silver Creek [Member] \| Silver Creek Series C Preferred Stock [Member] \| Prior to the Achievement of Milestone Event 1 [Member]
Debt Instrument [Line Items]
Warrants exercise price per share	$ 1.75			$ 1.75
Silver Creek [Member] \| Silver Creek Series C Preferred Stock [Member] \| On or After the Achievement of Milestone Event 1 [Member]
Debt Instrument [Line Items]
Warrants exercise price per share	$ 2.25			$ 2.25
Silver Creek [Member] \| Silver Creek Series C Preferred Stock [Member] \| Milestone Event 2 [Member]
Debt Instrument [Line Items]
Number of warrants exercisable	700			700
Description of milestone event achievement				Milestone Event 2 is defined as the date that is seven business days following the date when Silver Creek completes a Phase 1 clinical trial provided, that if Silver Creek receives proceeds of less than $4.0 million pursuant to the sale of Series C preferred stock, Milestone Event 2 shall mean the date that is seven business days following the first dose in humans in a clinical trial.
Silver Creek [Member] \| Silver Creek Series C Preferred Stock [Member] \| Prior to the Achievement of Milestone Event 2 [Member]
Debt Instrument [Line Items]
Warrants exercise price per share	$ 2.25			$ 2.25
Silver Creek [Member] \| Silver Creek Series C Preferred Stock [Member] \| On or After the Achievement of Milestone Event 2 [Member]
Debt Instrument [Line Items]
Warrants exercise price per share	2.75			2.75
Silver Creek [Member] \| Silver Creek Series C Preferred Stock [Member] \| Convertible Notes [Member]
Debt Instrument [Line Items]
Debt instrument conversion price per share	$ 1.50			$ 1.50
Preferred stock issued	1,500			1,500
Preferred stock price per share	$ 1.50			$ 1.50
Debt conversion, shares issued	800
Silver Creek [Member] \| Maximum [Member] \| Silver Creek Series C Preferred Stock [Member] \| Milestone Event 2 [Member]
Debt Instrument [Line Items]
Proceeds from sale of preferred stock				$ 4,000,000
Silver Creek Convertible Note [Member] \| Silver Creek [Member]
Debt Instrument [Line Items]
Gross proceeds from the debt issuance			$ 1,600,000			$ 1,000,000	$ 900,000
Interest rate (as a percent)	6.00%			6.00%
Discount on automatic conversion into the next qualifying equity financing (as a percent)			25.00%
Derivative liability			$ 200,000
Aggregate principal amount						$ 1,000,000
Silver Creek Convertible Note [Member] \| Silver Creek [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Amount of gross proceeds from qualifying equity financing in which holders would automatically convert into the next qualifying equity financing at a 25% discount			$ 4,000,000

Borrowings - Schedule of Future Minimum Payments under the Loans Payable (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 216,861	$ 257,655
Convertible Notes [Member]
Debt Instrument [Line Items]
2017	2,736
2018	2,736
2019	2,736
2020	63,527
Loans payable, gross including contractual interest	71,735
Less interest	(10,943)
Less unamortized discount	(13,842)
Long-term debt	46,950
2022 Notes [Member]
Debt Instrument [Line Items]
2017	20,125
2018	20,125
2019	62,617
2020	57,586
2021 and thereafter	100,078
Loans payable, gross including contractual interest	260,531
Less interest	(85,531)
Less unamortized discount	(5,089)
Long-term debt	$ 169,911

Restructuring Activities - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
	Oct. 03, 2016	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016
Restructuring Cost And Reserve [Line Items]
Reduction in headcount, percent	22.00%
Restructuring activity, announcement date				Oct. 03, 2016
Restructuring expenses		$ 5,047	$ 809	$ 5,856
Restructuring activities, description				One-time employee termination benefits were comprised of severance, benefits and related costs, all of which resulted in cash expenditures during the third and fourth quarters of 2016.
Stock-based Compensation Expense, Contractual Termination Benefits and One-time Employee Termination Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses				$ 5,900

Restructuring Activities - Summary of Charges Related to Restructuring Activities (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016
Restructuring Cost And Reserve [Line Items]
Expenses	$ 5,047	$ 809	$ 5,856
Less: Payments			(3,711)
Less: Non-Cash Expenses			(1,371)
Accrued Restructuring Expenses	774		774
Severance Benefits and Related Costs Due to Workforce Reduction [Member]
Restructuring Cost And Reserve [Line Items]
Expenses			5,856
Less: Payments			(3,711)
Less: Non-Cash Expenses			(1,371)
Accrued Restructuring Expenses	$ 774		$ 774

Common Stock Warrants - Schedule of Common Stock Warrant Activity of the Company (Detail) - Common Stock Warrant [Member] - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Beginning Balance	2,381	2,777
Exercised (in shares)	(2,355)	(396)
Cancelled (in shares)	(26)
Ending Balance		2,381
Beginning Balance	$ 3.00	$ 3.05
Exercised (per share)	3.00	3.38
Cancelled (per share)	$ 3.00
Ending Balance		$ 3.00

Common Stock - Additional Information (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Jul. 13, 2015	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2016
Class of Stock [Line Items]
Net proceeds from issuance of common stock after deducting commissions and offering expenses			$ 38,560,000
Common stock, shares issued			115,871,000	130,197,000
Common stock, shares authorized			200,000,000	200,000,000
Common stock, par value			$ 0.01	$ 0.01
Common stock, shares outstanding			115,871,000	130,197,000
Cowen and Company LLC [Member] \| At the Market Offering [Member]
Class of Stock [Line Items]
Net proceeds from issuance of common stock after deducting commissions and offering expenses		$ 38,600,000
Common stock, shares issued		3,800,000
Maximum [Member] \| Cowen and Company LLC [Member] \| At the Market Offering [Member]
Class of Stock [Line Items]
Aggregate sales price of offering	$ 40,000,000

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended
	Feb. 29, 2016	Feb. 28, 2015	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Granted				4,258,000
Weighted-average grant date fair value per share of stock options				$ 3.32	$ 5.80	$ 3.41
Aggregate intrinsic value of options exercised				$ 5.6	$ 30.9	$ 19.8
Unrecognized stock-based compensation expense related to nonvested stock options				$ 12.7
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized				1 year 8 months 12 days
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term				10 years
Stock Incentive Plan 2011 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional common stock available for issuance (in shares)	4,100,000	3,700,000	3,600,000
Shares of common stock available for grant (in shares)				4,700,000
Number of Options, Granted				4,300,000	3,700,000	3,900,000
Stock Incentive Plan 2011 [Member] \| Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period				3 years

Stock-Based Compensation - Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees (Detail) - Options to Purchase Common Stock [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.10%	1.50%	1.60%
Expected volatility	67.00%	66.00%	64.00%
Expected term	5 years	5 years	5 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.00%	1.80%	2.00%
Expected volatility	69.00%	67.00%	72.00%
Expected term	5 years 9 months 18 days	5 years 10 months 24 days	5 years 10 months 24 days

Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 15,205	$ 15,293	$ 12,929
Stock-based compensation expense for non-employee awards	1	58	268
Less: stock-based compensation expense capitalized to inventory	(341)
Total stock-based compensation expense	14,865	15,351	13,197
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	6,503	8,271	6,864
Selling, General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	7,331	$ 7,022	$ 6,065
Restructuring Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 1,371

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Options, Outstanding, Beginning balance	19,211
Number of Options, Granted	4,258
Number of Options, Exercised	(1,958)
Number of Options, Forfeited	(2,487)
Number of Options, Outstanding, Ending balance	19,024	19,211
Number of Options, Vested and expected to vest	18,794
Number of Options, Exercisable	14,968
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 5.72
Weighted-Average Exercise Price, Granted	5.57
Weighted-Average Exercise Price, Exercised	3.29
Weighted-Average Exercise Price, Forfeited	7.04
Weighted-Average Exercise Price, Outstanding, Ending balance	5.77	$ 5.72
Weighted-Average Exercise Price, Vested and expected to vest	5.76
Weighted-Average Exercise Price, Exercisable	$ 5.49
Weighted-Average Remaining Contractual Term	5 years 11 months 19 days	6 years 2 months 27 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	5 years 11 months 5 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 2 months 27 days
Aggregate Intrinsic Value, Outstanding	$ 7,564	$ 47,963
Aggregate Intrinsic Value, Vested and expected to vest	7,564
Aggregate Intrinsic Value, Exercisable	$ 7,564

Income Taxes - Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal income tax at statutory federal rate	35.00%	35.00%	35.00%
State taxes	0.70%	1.00%	3.10%
Permanent differences	(11.60%)	(6.40%)	(9.10%)
Stock-based compensation	(2.20%)	(1.30%)	(1.70%)
Tax credits	28.00%	21.30%	30.50%
Foreign rate differential			(2.30%)
Change in deferred state tax rate	(0.30%)	(2.30%)
Other	4.50%	(0.50%)	4.50%
Change in valuation allowance	(54.10%)	(46.80%)	(60.00%)

Income Taxes - Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets
Net operating losses	$ 194,027	$ 182,992
Capitalized research and development expenses	15,854	21,444
Credit carryforwards	144,823	93,113
Depreciation	2,557	2,128
Deferred compensation	12,463	11,664
Accrued expenses	3,601	1,807
Deferred revenue	21,935	10,999
Other temporary differences	25,276	17,235
Total gross deferred tax assets	420,536	341,382
Valuation allowance	(414,558)	(326,577)	$ (257,489)	$ (207,304)
Net deferred tax assets	5,978	14,805
Deferred tax liabilities
Intangible assets	(1,428)	(2,667)
Debt discount	$ (4,550)	$ (12,138)

Income Taxes - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Operating Loss Carryforwards [Line Items]
Federal and state net operating loss carryforwards relate to deductions for stock option compensation	$ 39.2
Federal Orphan Drug Credits	106.4
Federal [Member]
Operating Loss Carryforwards [Line Items]
NOL	542.7
Federal [Member] \| Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	27.3
State [Member]
Operating Loss Carryforwards [Line Items]
NOL	367.4
Federal and state net operating loss carryforwards relate to deductions for stock option compensation	25.2
State [Member] \| Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	16.3
State [Member] \| Investment [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 0.8

Commitments and Contingencies - Additional Information (Detail) $ in Millions		12 Months Ended
	May 31, 2016 ft²	Dec. 31, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Operating Leased Assets [Line Items]
Description of operating lease amendment		The Amended Lease will terminate on June 30, 2019, but the Company retains an option to renew the Amended Lease with respect to all of the leased space for an additional period of five years.
Aggregate space that the entity will lease under the amended lease agreement \| ft²		167,000
Sublease Agreement [Member]
Operating Leased Assets [Line Items]
Description of operating lease amendment		The Sublease terminates on December 31, 2017, but may be extended through June 30, 2019 if mutually agreed upon by the Company and the subtenant.
Area of office and lab \| ft²	8,143
Lease expiration date	Dec. 31, 2017
Lease extended date	Jun. 30, 2019
Operating leases, future minimum rental payments receivable		$ 0.6
Total rent expense		8.6	$ 7.4	$ 5.9
July 31, 2015 Amendment [Member]
Operating Leased Assets [Line Items]
Aggregate landlord reimbursable tenant improvements received under the existing lease and the lease amendment		$ 9.5

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2017	$ 8,108
2018	8,102
2019	4,082
Total future minimum lease payments	$ 20,292

Related Party Transactions - Additional Information (Detail) - shares	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Preferred stock issued	0	0
Silver Creek [Member] \| Series A and B Preferred Stock [Member]
Related Party Transaction [Line Items]
Shares owned by employees and directors of the parent company (as a percent)	7.00%	7.00%
Silver Creek [Member] \| Series C Preferred Stock [Member]
Related Party Transaction [Line Items]
Preferred stock issued	0

Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Product revenues, net	$ 15,752	$ 14,493	$ 12,851	$ 9,968	$ 4,328				$ 53,064	$ 4,328
License and collaboration revenues	44,057	12,417	19,332	11,313	17,090	$ 16,440	$ 36,558	$ 14,842	87,119	84,930	$ 102,756
Other revenues	1,431	1,161	1,498						4,090
Cost of revenues	3,319	1,010	1,872	711	46				6,912	46
Research and development expenses	54,961	32,078	40,996	32,882	44,740	37,763	42,806	35,679	160,917	160,988	138,495
Selling, general and administrative expenses	24,206	18,048	20,680	17,795	19,335	16,956	12,315	9,189	80,729	57,795	30,517
Restructuring expenses	5,047	809							5,856
Net loss	(33,627)	(30,275)	(50,958)	(38,658)	(48,068)	(42,386)	(22,901)	(34,432)	(153,518)	(147,787)	(83,559)
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$ (32,449)	$ (30,068)	$ (50,750)	$ (38,473)	$ (47,826)	$ (42,594)	$ (22,778)	$ (34,759)	$ (151,740)	$ (147,957)	$ (83,291)
Net loss per share available to common stockholders—basic and diluted	$ (0.25)	$ (0.23)	$ (0.40)	$ (0.33)	$ (0.41)	$ (0.38)	$ (0.21)	$ (0.32)	$ (1.21)	$ (1.33)	$ (0.80)

Going Concern - Additional Information (Detail) - USD ($)		12 Months Ended
	Jan. 07, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Unrestricted cash and cash equivalents		$ 21,524,000	$ 185,606,000	$ 35,688,000	$ 65,086,000
Aggregate principal amount outstanding to be redeemed			$ 40,000,000
Substantial doubt about going concern, conditions and events		The consummation of the asset sale with Ipsen is contingent upon approval by the Company’s stockholders as well as other customary closing conditions. If the asset sale is not consummated, the Company will not receive the $575.0 million upfront cash payment from Ipsen, and the Company will need to obtain additional funding through public or private debt or equity financings, through existing or new collaboration arrangements, or through divestitures of its assets.
Substantial doubt about going concern, within one year		true
Subsequent Event [Member] \| Asset Sale Agreement [Member] \| Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Special cash dividend to be paid	$ 200,000,000
Subsequent Event [Member] \| Asset Sale Agreement [Member] \| 2022 Notes [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate principal amount outstanding to be redeemed	175,000,000
Additional premium payment	20,100,000
Subsequent Event [Member] \| Ipsen [Member] \| Asset Sale Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront cash payment to be received	575,000,000
Subsequent Event [Member] \| Baxalta [Member] \| License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net milestone payments expected to be received	$ 33,000,000

Subsequent Events - Additional Information (Detail) shares in Thousands						3 Months Ended		12 Months Ended
	Feb. 23, 2017	Feb. 06, 2017 USD ($) shares	Jan. 09, 2017 USD ($) Employee	Jan. 07, 2017 USD ($) ft²	Nov. 08, 2016	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) shares
Subsequent Event [Line Items]
Restructuring activity, announcement date								Oct. 03, 2016
Restructuring expenses						$ 5,047,000	$ 809,000	$ 5,856,000
Restructuring activities, description								One-time employee termination benefits were comprised of severance, benefits and related costs, all of which resulted in cash expenditures during the third and fourth quarters of 2016.
Option grant to purchase common stock \| shares								4,258
BioPharma Credit Investments IV Sub, LP (“Pharmakon”) [Member] \| Credit Agreement [Member]
Subsequent Event [Line Items]
Credit facility, expiration date					Mar. 15, 2017
January 2017 Corporate Restructuring [Member]
Subsequent Event [Line Items]
Restructuring activity, announcement date								Jan. 09, 2017
Restructuring and related activities, completion date								Mar. 10, 2017
January 2017 Corporate Restructuring [Member] \| One-time Employee Termination Benefits [Member]
Subsequent Event [Line Items]
Restructuring activities, description								One-time employee termination benefits are comprised of severance, benefits and related costs, all of which are expected to result in cash expenditures. The specific timing of the incurrence and payment of these restructuring expenses is dependent upon the timing of the closing of the asset sale.
Asset Sale Agreement [Member]
Subsequent Event [Line Items]
Assets sales termination fee description								The termination fee will also be payable if the Asset Sale Agreement is terminated because the Company’s stockholders did not vote to adopt the Asset Sale Agreement and, prior to such termination, a proposal to acquire at least 50% of the consolidated assets of the Company with respect to the Commercial Business or at least 50% of the Company’s voting securities has been publicly disclosed and the Company enters into a definitive agreement with respect to such proposal within 12 months after such termination, which is subsequently consummated.
Subsequent Event [Member] \| BioPharma Credit Investments IV Sub, LP (“Pharmakon”) [Member] \| Credit Agreement [Member]
Subsequent Event [Line Items]
Credit facility, expiration date	Apr. 27, 2017
Subsequent Event [Member] \| Chief Executive Officer [Member]
Subsequent Event [Line Items]
Annual base salary		$ 700,000
Employment agreement description		Dr. Peters will receive an annual base salary of $700,000 and is eligible for an annual bonus of up to 65% of his base salary. Dr. Peters also received a one-time signing bonus of $900,000. Subject to the further approval of the Company’s Board of Directors, the Company will also grant Dr. Peters an option to purchase a number of shares of the Company’s common stock equal to the lesser of (i) such number of shares that has a target grant date fair value of $3.5 million and (ii) 2.0 million shares, with an exercise price per share equal to the fair market value of the Company’s common stock on the date of grant.
One-time signing bonus		$ 900,000
Target grant date fair value		$ 3,500,000
Option grant to purchase common stock \| shares		2,000
Option vesting description		The option will vest over four years at the rate of 25% on February 6, 2018 and the remainder in equal quarterly installments over the following three years.
Subsequent Event [Member] \| Chief Executive Officer [Member] \| Tranche 1 [Member]
Subsequent Event [Line Items]
Options vesting period		4 years
Option vesting percentage		25.00%
Option vesting date		Feb. 06, 2018
Subsequent Event [Member] \| Chief Executive Officer [Member] \| Tranche 2 [Member]
Subsequent Event [Line Items]
Remainder period for vesting option		3 years
Subsequent Event [Member] \| January 2017 Corporate Restructuring [Member]
Subsequent Event [Line Items]
Restructuring and related cost, number of expected employees after headcount reduction \| Employee			80
Subsequent Event [Member] \| Maximum [Member] \| Chief Executive Officer [Member]
Subsequent Event [Line Items]
Percentage of eligible annual bonus on base salary		65.00%
Subsequent Event [Member] \| Maximum [Member] \| January 2017 Corporate Restructuring [Member] \| One-time Employee Termination Benefits [Member]
Subsequent Event [Line Items]
Restructuring expenses			$ 8,500,000
Subsequent Event [Member] \| Minimum [Member] \| January 2017 Corporate Restructuring [Member] \| One-time Employee Termination Benefits [Member]
Subsequent Event [Line Items]
Restructuring expenses			$ 7,500,000
Subsequent Event [Member] \| Asset Sale Agreement [Member]
Subsequent Event [Line Items]
Payment of termination fee				$ 25,000,000
Minimum percentage of consolidated assets in commercial business				50.00%
Minimum percentage of voting securities				50.00%
Subsequent Event [Member] \| Baxalta [Member] \| License and Collaboration Agreements [Member]
Subsequent Event [Line Items]
Net milestone payments entitled to receive				$ 33,000,000
Subsequent Event [Member] \| Ipsen [Member] \| Asset Sale Agreement [Member]
Subsequent Event [Line Items]
Upfront cash payment to be received				$ 575,000,000
Subsequent Event [Member] \| Ipsen [Member] \| Asset Sale Agreement [Member] \| Manufacturing Facility [Member]
Subsequent Event [Line Items]
Area of sublease property \| ft²				68,409
Subsequent Event [Member] \| Ipsen [Member] \| Asset Sale Agreement [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Additional payments receivable on achievement of certain milestone events				$ 450,000,000
Out-of-pocket expenses to be paid				$ 3,000,000

Retirement Plan	12 Months Ended
Retirement Plan	Dec. 31, 2016
Postemployment Benefits [Abstract]
Retirement Plan	20. Retirement Plan On May 31, 2002, the Company established a 401(k) defined contribution savings plan (the “401(k) Plan”) for its employees who meet certain service period and age requirements. Contributions are permitted up to the maximum allowed under the Internal Revenue Code of each covered employee’s salary. The 401(k) Plan permits the Company to contribute at its discretion. For the years ended December 31, 2016, 2015 and 2014, the Company made contributions of $1.3 million, $1.1 million and $0.8 million, respectively, to the 401(k) Plan.

Inventory - Additional Information (Detail) $ in Millions	12 Months Ended
Inventory - Additional Information (Detail) $ in Millions	Dec. 31, 2016 USD ($)
Cost of Revenues [Member]
Inventory [Line Items]
Aggregate charges related to excess and scrap inventory and excess manufacturing capacity	$ 3.6

Common Stock Warrants - Additional Information (Detail) - Common Stock Warrant [Member] - shares	Dec. 31, 2015	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Number of warrants cashless exercised	2,295,000	75,000
Number of common stock issued as a result of cashless exercise of warrants	1,695,000	38,000