Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Mar. 07, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
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	Accelerated Filer
Entity Common Stock, Shares Outstanding		13,342,784
Entity Public Float			$ 157,909,117

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 93,441	$ 21,524
Restricted cash	102	102
Accounts receivable, net	100	275
Prepaid expenses and other current assets	1,403	2,239
Assets held for sale		33,295
Total current assets	95,046	57,435
Restricted cash	674	674
Property and equipment, net	6,467	14,212
Equity method investment	10,551
Other assets	4,588	27
Long-term assets held for sale		9,135
Total assets	117,326	81,483
Current liabilities:
Accounts payable, accrued expenses and other	17,606	28,670
Deferred rent	2,171	2,014
Liabilities held for sale		57,538
Total current liabilities	19,777	88,222
Deferred rent, net of current portion	1,209	3,386
Long-term debt, net of current portion		216,861
Long-term liabilities held for sale		25,673
Other long-term liabilities	56
Total liabilities	21,042	334,142
Commitments and contingencies (Note 16)
Non-controlling interest		(1,539)
Stockholders’ equity (deficit):
Preferred stock, $0.01 par value: 10,000 shares authorized at December 31, 2017 and 2016; no shares issued or outstanding at December 31, 2017 or 2016
Common stock, $0.01 par value: 20,000 shares authorized at December 31, 2017 and 2016, 13,343 and 13,020 issued and outstanding at December 31, 2017 and 2016, respectively	1,334	1,302
Additional paid-in capital	577,721	702,377
Accumulated deficit	(482,771)	(954,799)
Total stockholders’ equity (deficit)	96,284	(251,120)
Total liabilities, non-controlling interest and stockholders’ equity (deficit)	$ 117,326	$ 81,483

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
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	20,000,000	20,000,000
Common stock, shares issued	13,343,000	13,020,000
Common stock, shares outstanding	13,343,000	13,020,000

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Costs and expenses:
Research and development expenses	$ 67,314	$ 109,565	$ 121,033
General and administrative expenses	28,452	32,052	24,048
Restructuring expenses	9,521	5,710
Total costs and expenses	95,766	147,327	145,081
Loss from continuing operations	(95,766)	(147,327)	(145,081)
Other income and expenses:
Interest income	895	276	99
Interest expense	(34,650)	(22,449)	(18,769)
Gain on deconsolidation of Silver Creek Pharmaceuticals, Inc.	10,848
Gain on sale of asset	1,703
Other (expense) income, net	(1,433)	(8)	917
Net loss from continuing operations before income tax benefit	(118,403)	(169,508)	(162,834)
Income tax benefit	42,399	13,224	11,215
Net loss from continuing operations	(76,004)	(156,284)	(151,619)
Discontinued operations:
Income from discontinued operations, net of tax	546,872	2,766	3,832
Net income (loss)	470,868	(153,518)	(147,787)
Net (loss) income attributable to non-controlling interest	(1,160)	(1,778)	170
Net income (loss) attributable to Merrimack Pharmaceuticals, Inc.	472,028	(151,740)	(147,957)
Other comprehensive income:
Unrealized gain on available-for-sale securities			74
Other comprehensive income			74
Comprehensive income (loss)	472,028	(151,740)	(147,883)
Amounts attributable to Merrimack Pharmaceuticals, Inc.:
Net loss from continuing operations	(74,844)	(154,506)	(151,789)
Income from discontinued operations, net of tax	$ 546,872	$ 2,766	$ 3,832
Basic and dilutive net income (loss) per common share
Net loss from continuing operations	$ (5.66)	$ (12.33)	$ (13.63)
Net income from discontinued operations, net of tax	41.33	0.22	0.34
Net income (loss) per share	$ 35.67	$ (12.11)	$ (13.29)
Weighted-average common shares used in per share calculations—basic and diluted	13,232	12,533	11,136
Cash dividend paid per common share	$ 10.55

Consolidated Statements of Non-Controlling Interest and Stockholders' Equity (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]	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]	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]	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2014	$ (102,140)				$ 69			$ 1,067		$ 552,037				$ (74)	$ (655,170)
Balance (in shares) at Dec. 31, 2014								10,670
Exercise of stock options and common stock warrants	10,101							$ 54		10,047
Exercise of stock options and common stock warrants (shares)								536
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)								381
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.		$ 1,188				$ 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 income (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								11,587
Exercise of stock options	6,442							$ 20		6,422
Exercise of stock options (shares)								196
Issuance of stock due to conversion of convertible notes				$ 100,961					$ 123				$ 100,838
Issuance of stock due to conversion of convertible notes (shares)									1,237
Consideration allocated to reacquisition of conversion feature on extinguishment of convertible notes due 2020	(39,923)									(39,923)
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.			$ 2,689				$ (827)					$ 2,689
Stock-based compensation	15,206									15,206
Loss attributable to non-controlling interest	951				(951)										951
Net income (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								13,020
Exercise of stock options	$ 6,689							$ 32		6,657
Exercise of stock options (shares)	323							323
Consideration allocated to reacquisition of conversion feature on extinguishment of convertible notes due 2020	$ (4,481)									(4,481)
Dividend paid	(140,000)									(140,000)
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.							$ 847
Stock-based compensation	13,168									13,168
Loss attributable to non-controlling interest	1,160				(1,160)										1,160
Deconsolidation of non-controlling interest	1,852				$ 1,852
Net income (loss)	470,868														470,868
Balance at Dec. 31, 2017	$ 96,284							$ 1,334		$ 577,721					$ (482,771)
Balance (in shares) at Dec. 31, 2017								13,343

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income (loss)	$ 470,868	$ (153,518)	$ (147,787)
Income from discontinued operations, net of tax	546,872	2,766	3,832
Loss from continuing operations	(76,004)	(156,284)	(151,619)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense	3,678	6,004	8,217
Non-cash loss on extinguishment	5,202	14,566
Non-cash activity related to discontinued operations	17,282	13,224	11,215
Benefit from intra period tax allocation	(42,399)	(13,224)	(11,215)
Loss on disposal of property and equipment		493	4
Gain on sale of property and equipment	(439)	(40)
Impairment of in-process research and development intangible asset		2,800
Depreciation and amortization expense	5,221	4,895	3,250
Stock-based compensation expense	12,788	12,140	13,161
Loss on equity method investment	849
Gain on deconsolidation of Silver Creek Pharmaceuticals, Inc.	(10,848)
Changes in operating assets and liabilities:
Accounts receivable	175	(264)	1,654
Prepaid expenses and other assets	(8,476)	2,184	(32)
Accounts payable, accrued expenses and other	(9,278)	(9,837)	13,163
Deferred rent and tax incentives	(2,021)	408	2,374
Net cash used in continuing operations for operating activities	(104,270)	(122,935)	(109,828)
Net cash (used in) provided by discontinuing operations for operating activities	(41,665)	(47,306)	4,472
Net cash used in operating activities	(145,935)	(170,241)	(105,356)
Cash flows from investing activities
Purchase of marketable securities		(84,262)
Proceeds from sales and maturities of marketable securities		84,160	87,899
Purchase of property and equipment	(915)	(2,640)	(11,902)
Proceeds on sale of property and equipment	1,094
Proceeds from sale of discontinued operations	580,714
Net cash provided by (used in) continuing operations for investing activities	576,891	(2,742)	75,997
Net cash used in discontinuing operations for investing activities		(515)	(887)
Net cash provided by (used in) investing activities	576,891	(3,257)	75,110
Cash flows from financing activities
Proceeds from exercise of options and warrants to purchase common stock	6,917	6,224	10,087
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.	3,994	3,361	2,083
Repayment of debt	(229,662)		(40,000)
Payment of dividend	(140,000)
Other financing activities, net	(288)	(169)
Net cash (used in) provided by financing activities	(359,039)	9,416	180,164
Net increase (decrease) in cash and cash equivalents	71,917	(164,082)	149,918
Cash and cash equivalents, beginning of period	21,524	185,606	35,688
Cash and cash equivalents, end of period	93,441	21,524	185,606
Non-cash investing and financing activities
Purchases of property and equipment in accounts payable, accrued expenses and other	14	130	816
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 due 2020 converted into shares of common stock		64,209
Supplemental disclosure of cash flows
Cash paid for income taxes	7,926
Cash paid for interest	30,966	$ 23,914	$ 10,087
Silver Creek Pharmaceuticals Inc [Member]
Adjustments to reconcile net loss to net cash used in operating activities
Loss on equity method investment	(800)
Gain on deconsolidation of Silver Creek Pharmaceuticals, Inc.	(10,848)
Cash flows from investing activities
Deconsolidation of Silver Creek Pharmaceuticals, Inc. cash	$ (4,002)

Nature of the Business and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

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 clinical stage biopharmaceutical company based in Cambridge, Massachusetts that is outthinking cancer by targeting biomarker-defined cancers. The Company’s vision is to ensure that cancer patients and their families live fulfilling lives. The Company’s mission is to transform cancer care through the smart design and development of targeted solutions based on a deep understanding of cancer pathways and biological markers. All of the Company’s development programs, including four clinical trials and six candidates in preclinical development, fit into the Company’s strategy of (1) understanding the biological problems it is trying to solve, (2) designing specific solutions against the problems it is trying to solve and (3) developing those solutions for biomarker-selected patients. This three-pronged strategy seeks to ensure optimal patient outcomes.

On April 3, 2017, the Company completed the previously announced asset sale (the “Asset Sale”) with Ipsen S.A. (“Ipsen”). Pursuant to the Asset Purchase and Sale Agreement, dated as of January 7, 2017 (the “Asset Sale Agreement”), between the Company and Ipsen, the Company sold to Ipsen its 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”). The Company received $575.0 million in cash, plus a working capital adjustment of $5.7 million, and is eligible to receive up to $450.0 million in additional regulatory approval-based milestone payments. The working capital adjustment of $5.7 million was agreed to with Ipsen and received by the Company in the year ended December 31, 2017. The Company also retained the right to receive net milestone payments that may become payable for the ex-U.S. development and commercialization of ONIVYDE for up to $33.0 million pursuant to a license and collaboration agreement (the “Baxalta Agreement”) with Baxalta Incorporated, Baxalta US Inc. and Baxalta GmbH (collectively, “Baxalta”). The Company entered into the Baxalta Agreement in 2014, and on April 3, 2017, the Baxalta Agreement was assigned to Ipsen in connection with the completion of the Asset Sale.

The Company’s non-commercial assets, including its clinical and preclinical development programs, were not included in the Asset Sale and remain assets of the Company. The Company’s most advanced assets and a description of the status of each asset is as follows:

•

MM-121 (seribantumab): MM-121 is a fully human monoclonal antibody that binds to the ErbB3 (HER3) receptor and targets heregulin positive cancers. There are two active development programs for MM-121, each in a Phase 2 clinical trial. The Company is currently conducting the global, open-label, biomarker-selected, Phase 2 randomized SHERLOC clinical trial, evaluating MM-121 in combination with docetaxel in patients with heregulin positive non-small cell lung cancer. The Company is also conducting the global, double-blinded, placebo-controlled, biomarker-selected, Phase 2 randomized SHERBOC clinical trial evaluating MM-121 in combination with fulvestrant in patients with heregulin positive, hormone receptor positive, ErbB2 (HER2) negative, metastatic breast cancer;

•

MM-141 (istiratumab): MM-141 is a fully human tetravalent bispecific antibody designed to block tumor survival signals by targeting receptor complexes containing the insulin-like growth factor 1 (“IGF-1”), receptor and ErbB3 (HER3) cell surface receptor. The Company is currently conducting and has completed enrollment of the global, double-blinded, placebo-controlled, Phase 2 randomized CARRIE clinical trial evaluating MM-141 in combination with nab-paclitaxel and gemcitabine in patients with previously untreated metastatic pancreatic cancer with high serum levels of free IGF-1; and

•

MM-310: MM-310 is an antibody-directed nanotherapeutic that contains a novel prodrug of the highly potent chemotherapy docetaxel and targets the ephrin receptor A2 receptor, which is highly expressed in most solid tumor types, such as prostate, ovarian, bladder, gastric, pancreatic and lung cancers. The Company initiated a Phase 1 clinical trial to evaluate safety and preliminary activity of MM-310 and to identify the maximum tolerated dose in the first quarter of 2017.

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 capital, adequate personnel, infrastructure and extensive compliance reporting capabilities.

The Company’s product candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies, among others. In addition, the Company is dependent upon the services of its employees and consultants.

In accordance with Accounting Standards Codification (“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. As of December 31, 2017 the Company had an accumulated deficit of $482.8 million. During the year ended December 31, 2017, the Company incurred a net loss from continuing operations of $76.0 million and used $104.3 million of cash in continuing operations for operating activities. The Company expects to continue to generate operating losses in the foreseeable future. The Company expects that its cash and cash equivalents of $93.4 million at December 31, 2017 will be sufficient to fund its operating expenses and capital expenditure requirements for at least the next 12 months from issuance of the financial statements. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations.

The Company will ultimately need to seek additional funding through public or private equity or debt 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.

Summary of Significant Accounting Policies

The Company’s significant accounting policies include policies related to both continuing and discontinuing operations.

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 (the United States).

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.

As of March 31, 2017, the Commercial Business met all the conditions to be classified as held-for-sale and represents a discontinued operation since the disposal of the Commercial Business is a strategic shift that will have a major effect on the Company’s operations and financial results. The Company will not have further significant involvement in the operations of the discontinued Commercial Business. The operating results of the Commercial Business are reported as discontinued operations, net of tax in the consolidated statements of operations and comprehensive income (loss) for all periods presented. In addition, in the consolidated balance sheet as of December 31, 2016, the assets and liabilities held for sale have been presented separately. For additional information, see Note 2, “Discontinued Operations – Sale of Commercial Business.”

The consolidated financial statements have historically included the accounts of the Company and Silver Creek Pharmaceuticals, Inc. (“Silver Creek”) with all intercompany transactions and balances eliminated in consolidation. Silver Creek represented a variable interest entity that the Company consolidated as the primary beneficiary. As discussed in Note 3, “Investment in Silver Creek,” Silver Creek completed a preferred stock financing in the third quarter of 2017, which reduced the Company’s ownership percentage in Silver Creek below 50% and resulted in the Company no longer controlling the Silver Creek board of directors. The Company determined that it is no longer the primary beneficiary of Silver Creek since the Company does not control the board of directors and does not direct the activities that have the most significant impact on Silver Creek’s economic performance. Therefore, the Company deconsolidated Silver Creek from its financial statements in the third quarter of 2017 in accordance with ASC 810-10-40-4(c), Consolidation. The Company accounts for its investment in Silver Creek under the equity method of accounting as of December 31, 2017.

The Company’s consolidated balance sheet as of December 31, 2016 included Silver Creek’s assets and liabilities, after intercompany eliminations. The Company’s consolidated balance sheet as of December 31, 2017 does not include the assets and liabilities of Silver Creek since the Company deconsolidated Silver Creek in the third quarter of 2017. The Company’s consolidated statements of operations and comprehensive income (loss) for the year ended December 31, 2017 include Silver Creek’s results for the period through July 13, 2017, the day immediately preceding the deconsolidation of Silver Creek.

On August 11, 2017, the Company’s stockholders approved an amendment to the Company's certificate of incorporation to effect a one-for-ten reverse stock split of its issued and outstanding common stock (the “Reverse Split”). On September 5, 2017, the Company filed an amendment to its certificate of incorporation to effect the Reverse Split, and on September 6, 2017, the Reverse Split was effective for trading purposes. As a result of the Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock, reducing the number of issued and outstanding shares of common stock from approximately 132.8 million shares to approximately 13.28 million shares. No fractional shares were issued in connection with the Reverse Split. The amendment to the certificate of incorporation also proportionately reduced the number of authorized shares of common stock from 200 million to 20 million. The Reverse Split did not change the par value of the common stock. The Reverse Split did not change the number of authorized shares or par value of the Company’s preferred stock, of which there are no shares issued or outstanding. All outstanding stock options and convertible notes entitling their holders to purchase shares of common stock or acquire shares of common stock upon conversion, as the case may be, were adjusted as a result of the Reverse Split, as required by the terms of these securities. This change is reflected throughout the financial statements as appropriate. As a result, all share and per share amounts have been adjusted retroactively to reflect the Reverse Split for all periods. For additional information, see Note 14, “Stock-Based Compensation.”

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, estimates utilized in the valuation of inventory, accounting for stock-based compensation 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.

Certain estimates, such as revenue 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, contingencies, intangible assets, goodwill and in-process research and development (“IPR&D”) related specifically to the Commercial Business, which has been reclassified under discontinued operations and included in assets and liabilities held for sale.

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, 2017 and 2016, the Company recorded restricted cash of $0.8 million and $0.8 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 are carried at fair value, with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity (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 income (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. The Company did not have any marketable securities as of December 31, 2017 or 2016.

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.

As a result of the Asset Sale, all inventory relates to the Commercial Business and has been reclassified under discontinued operations.

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.

As a result of the Asset Sale, all goodwill and intangible assets relate to the Commercial Business and have been reclassified under discontinued operations.

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.

As discussed in Note 3, “Investment in Silver Creek,” Silver Creek completed a preferred stock financing in the third quarter of 2017, which reduced the Company’s ownership percentage in Silver Creek below 50% and resulted in the Company no longer controlling the Silver Creek board of directors. The Company determined that it is no longer the primary beneficiary of Silver Creek since the Company does not control the board of directors and does not direct the activities that have the most significant impact on Silver Creek’s economic performance. Therefore, the Company deconsolidated Silver Creek from its financial statements in the third quarter of 2017 in accordance with ASC 810-10-40-4(c), Consolidation.

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

Prior to the Asset Sale, the Company sold ONIVYDE to a limited number of specialty pharmaceutical distributors in the United States (collectively, its “Distributors”). The Company’s Distributors subsequently resold the products to healthcare providers. The Company recognized revenue on product sales when title and risk of loss had passed to the Distributor, which was typically upon delivery. Product revenues were recorded net of applicable reserves for discounts and allowances. As a result of the Asset Sale, all product revenues relate to the Commercial Business and have been reclassified under discontinued operations.

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 estimated 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 were based on estimates of the amounts earned or to be claimed on the related sales. The Company’s estimates took 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 varied, the Company would 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 paid fees to its Distributors for providing certain data to the Company as well as for maintaining contractual inventory and service levels. These trade allowances were recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized.

Rebates and Chargeback Discounts: The Company was 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 estimated the rebates and chargeback discounts it provided to Third-party Payors, based upon its estimated payor mix, and deducted these estimated amounts from its gross product revenues at the time revenue was recognized. Chargeback discounts were processed when the Third-party Payor purchased the product at a discount from the Distributor, who then in turn charged 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 were recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue was recognized. Rebates that were invoiced directly to the Company were recorded as accrued liabilities on the consolidated balance sheet at the time revenue was recognized.

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

Other Incentives: The Company offered co-pay mitigation support to commercially insured patients. The Company’s co-pay mitigation program was 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 estimated average co-pay mitigation amounts in order to establish a reserve for co-pay mitigation claims and deducted these estimated amounts from its gross product revenues at the later of the date that (i) the revenues were recognized or (ii) the incentive was offered. Claims under the Company’s co-pay mitigation program were subject to expiration.

All product revenue recognized relates to the Commercial Business and is presented as income from discontinued operations, net of tax in the consolidated statements of operations and comprehensive income (loss) for all periods presented. In addition, in the consolidated balance sheet as of December 31, 2016, the balance sheet accounts described above are included in assets and liabilities held for sale.

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 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 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 development, license and supply agreement (the “Actavis Agreement”) with Watson Laboratories, Inc. (“Actavis”) in November 2013, which was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements.

All operating results recognized related to the Baxalta Agreement and Actavis Agreement are presented as income from discontinued operations, net of tax in the consolidated statements of operations and comprehensive income (loss) for all periods presented. In addition, in the consolidated balance sheet as of December 31, 2016, the assets and liabilities related to the Baxalta Agreement and Actavis Agreement have been presented separately as assets and liabilities held for sale. Both the Baxalta Agreement and Actavis Agreement were assigned to Ipsen in connection with the completion of the Asset Sale.

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

Prior to the Asset Sale, the Company was a party to separate commercial supply agreements with Baxalta and PharmaEngine, Inc. (“PharmaEngine”) pursuant to which the Company supplied ONIVYDE to these entities. Revenue was recognized under these commercial supply arrangements when the counterparty took delivery of the commercial supply product and when the other general revenue recognition criteria outlined above were met. The Baxalta Agreement and the PharmaEngine agreement were assigned to Ipsen in connection with the completion of the Asset Sale.

The Company was 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.

All other revenue recognized relates to the Commercial Business and is presented as income from discontinued operations, net of tax in the consolidated statements of operations and comprehensive income (loss) for all periods presented.

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.

General and Administrative Expenses

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 general and administrative expenses include costs for 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.

Stock-Based Compensation Expense

The Company accounts for its stock-based compensation awards in accordance with 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 income (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 other income or expense related to tax incentive awards other income or expense-related items as components of “Other (expense) income, net” within the consolidated statements of operations and comprehensive income (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 12, “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 $1.4 million. Such amounts have been classified as current liabilities as of December 31, 2017.

The Company recognized $0.1 million and $0.7 million in income related to these MLSC tax incentives during the years ended December 31, 2016 and 2015, respectively. No income was recognized during the year ended December 31, 2017.

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 in money market funds. 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.

No customer individually accounted for 10% or more of total gross revenues or total gross accounts receivable for the years ended December 31, 2017, 2016 or 2015.

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 collectability, 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 does not have any revenue generating contracts with customers due to the sale of the Commercial Business in 2017 and therefore does not expect adoption of the new revenue standard to have a material impact on the consolidated financial statements. The Company will adopt the new revenue standard on January 1, 2018 using the modified retrospective approach.

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 will adopt this guidance as of the required effective date of January 1, 2018 and does not anticipate that the adoption will have a material impact to the consolidated financial statements.

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 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 will adopt ASU 2016-15 as of the required effective date of January 1, 2018 and is currently evaluating the potential impact that the adoption of this guidance may have on the consolidated financial statements.

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 May 2017, the FASB issued ASU 2017-09, “Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting,” which provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in ASU 2017-09. The standard should be applied prospectively to awards modified on or after the adoption date. This guidance will be effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted, including adoption in any interim period. The Company will adopt ASU 2017-09 as of the required effective date of January 1, 2018. The adoption of ASU 2017-09 will have an impact on the accounting for the modification of stock-based awards, if any, after the date of adoption.

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.

Discontinued Operations - Sale of Commercial Business

12 Months Ended

Dec. 31, 2017

Discontinued Operations And Disposal Groups [Abstract]

Discontinued Operations - Sale of Commercial Business

2. Discontinued Operations - Sale of Commercial Business

Ipsen

As of March 31, 2017, the Commercial Business met all the conditions to be classified as held-for-sale and represents a discontinued operation since the disposal of the Commercial Business is a strategic shift that will have a major effect on the Company’s operations and financial results. The Company will not have further significant involvement in the operations of the discontinued Commercial Business. The operating results of the Commercial Business are reported as discontinued operations, net of tax in the consolidated statements of operations and comprehensive income (loss) for all periods presented. In addition, in the consolidated balance sheet as of December 31, 2016, the assets and liabilities held for sale have been presented separately. This change is reflected throughout the financial statements as appropriate.

As discussed in Note 1, “Nature of the Business and Summary of Significant Accounting Policies,” on April 3, 2017, the Company completed the sale of the Commercial Business to Ipsen. Pursuant to the Asset Sale Agreement, the Company may be entitled to up to $450.0 million in additional payments based on the achievement by or on behalf of Ipsen of certain milestone events if the U.S. Food and Drug Administration (the “FDA”) approves ONIVYDE for certain indications as follows: (i) $225.0 million upon the regulatory approval by the FDA of ONIVYDE for the first-line treatment of metastatic adenocarcinoma of the pancreas (a) in combination with fluorouracil and leucovorin (with or without oxaliplatin), (b) in combination with gemcitabine and abraxane or (c) following submission and filing of regulatory approval by Ipsen for purposes of commercialization by Ipsen; (ii) $150.0 million upon the regulatory approval by the FDA of ONIVYDE for the treatment of small cell lung cancer after failure of first-line chemotherapy; and (iii) $75.0 million upon the regulatory approval by the FDA of ONIVYDE for an additional indication unrelated to those described above.

Discontinued Operations and Assets Held for Sale

The consolidated financial statements for the years ended December 31, 2017, 2016 and 2015 reflect the operations of the Commercial Business as a discontinued operation. Discontinued operations for the years ended December 31, 2017, 2016 and 2015 includes the following:

(in thousands)	Years Ended December 31,
	2017			2016			2015
Revenues:
Product revenues, net	$	16,135		$	53,064		$	4,328
License and collaboration revenues		7,797			87,119			84,930
Other revenues		1,973			4,090			—
Total revenues		25,905			144,273			89,258
Costs and expenses:
Cost of revenues		3,890			6,912			46
Research and development expenses		3,002			51,352			39,955
Selling, general and administrative expenses		10,907			48,677			33,747
Restructuring expenses		9,535			146			—
Total costs and expenses		27,334			107,087			73,748
Other income and expenses:
Interest expense		(6,743	)		(21,196	)		(463	)
Gain on sale of Commercial Business		601,670			—			—
Income from discontinued operations	$	593,498		$	15,990		$	15,047
Income tax expense		(46,626	)		(13,224	)		(11,215	)
Total income from discontinued operations	$	546,872		$	2,766		$	3,832

The carrying value of the assets and liabilities of the Commercial Business classified as “Assets held for sale” in the consolidated balance sheets are as follows:

(in thousands)	December 31, 2016
Assets
Current assets:
Accounts receivable, net	$	17,194
Inventory		14,554
Prepaid expenses and other current assets		1,547
Total current assets held for sale		33,295
Property and equipment, net		1,553
Intangible assets, net		3,977
Goodwill		3,605
Total long-term assets held for sale		9,135
Liabilities
Current liabilities:
Accounts payable, accrued expenses and other		21,312
Deferred revenues		36,226
Total current liabilities held for sale		57,538
Deferred revenues, net of current portion		25,673
Total long-term liabilities held for sale		25,673

The Company has reclassified approximately $0.6 million of accounts payable, accrued expenses and other from continuing operations to discontinuing operations for the year ended December 31, 2016.

Investment in Silver Creek

12 Months Ended

Dec. 31, 2017

Noncontrolling Interest [Abstract]

Investment in Silver Creek

3. Investment in Silver Creek

On August 20, 2010, the Company acquired a controlling financial interest in Silver Creek. At such time, the Company had the ability to direct the activities of Silver Creek that most significantly impacted Silver Creek’s economic performance through its ownership percentage and through the board of director seats controlled by the Company. As such, Silver Creek was consolidated by the Company.

Since the Company acquired its financial interest, Silver Creek has raised funding through the issuance of Series A, B and C preferred stock. The Company has not participated in any Silver Creek financings nor has it provided any funding since the Company acquired its financial interest. As of December 31, 2016, the Company held an ownership interest in Silver Creek greater than 50% and maintained the ability to control the board of directors and the activities that most significantly impacted the economic performance of Silver Creek.

During the third quarter of 2017, Silver Creek completed its Series C preferred stock financing, which reduced the Company’s ownership percentage in Silver Creek below 50% and resulted in the Company no longer controlling the Silver Creek board of directors. As of December 31, 2017, the Company’s ownership percentage in Silver Creek was approximately 43%. The Company determined that it is no longer the primary beneficiary of Silver Creek since the Company does not control the board of directors and does not direct the activities that have the most significant impact on Silver Creek’s economic performance. Therefore, the Company deconsolidated Silver Creek from its financial statements on July 13, 2017 in accordance with ASC 810-10-40-4(c), Consolidation. Starting on July 14, 2017, the Company accounted for its investment in Silver Creek under the equity method of accounting as it has the ability to exercise significant influence over Silver Creek. Under the equity method of accounting, the Company will record its proportionate share of the investee’s earnings (losses) in its results of operations with a corresponding increase (decrease) in the carrying value of the investment.

The Company recorded a gain on the deconsolidation of Silver Creek of $10.8 million for the year ended December 31, 2017 in the consolidated statement of operations and comprehensive income (loss). On the date of deconsolidation, the fair value of the Company’s investment in Silver Creek exceeded the Company’s share of the net assets of Silver Creek, which generated the gain. On July 14, 2017, the Company recorded its investment in Silver Creek at a fair value of $11.4 million, which was based on a third party valuation report. The gain on deconsolidation includes the following:

(in thousands)
Fair value of the Company's retained investment in Silver Creek	$	11,400
Carrying value of non-controlling interest		(1,852	)
Derecognition of Silver Creek's net liabilities		1,300
Gain recognized on deconsolidation of Silver Creek	$	10,848

The change in the non-controlling interest related to Silver Creek was as follows:

(in thousands)	Non- Controlling Interest
Balance at December 31, 2016	$	(1,539	)
Net loss attributable to Silver Creek through July 13, 2017		(1,160	)
Issuance of Silver Creek Series C preferred stock		847
Balance at date of deconsolidation		(1,852	)
Carrying value of non-controlling interest		1,852
Balance at December 31, 2017	$	—

(in thousands)	Non- Controlling Interest
Balance at December 31, 2015	$	239
Issuance of Silver Creek Series C preferred stock		(827	)
Net loss attributable to Silver Creek		(951	)
Balance at December 31, 2016	$	(1,539)

As of December 31, 2017, the Company held an equity investment in Silver Creek, which was accounted for as an equity method investment. The carrying value of the investment in Silver Creek was $10.6 million at December 31, 2017. During the year ended December 31, 2017, the Company recorded a loss associated with Silver Creek of $0.8 million as a component of other (expense) income, net in the consolidated statements of operations and comprehensive income (loss), representing its proportionate share of Silver Creek’s losses from July 14, 2017 through December 31, 2017.

Net Loss Per Common Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Loss Per Common Share

4. Net Loss Per Common Share

Basic net income (loss) per share is calculated by dividing the net income (loss) attributable to Merrimack Pharmaceuticals, Inc. by the weighted-average number of common shares outstanding during the period.

Diluted net income (loss) per share is computed by dividing the net income (loss) attributable to Merrimack Pharmaceuticals, Inc. by the weighted-average number of dilutive common shares outstanding during the period. Dilutive shares outstanding is calculated by adding to the weighted shares outstanding any potential (unissued) shares of common stock from outstanding stock options based on the treasury stock method. In a period when a net loss is reported, all common stock equivalents are excluded from the calculation because they would have an anti-dilutive effect, meaning the loss per share would be reduced. Therefore, in periods where a loss is reported, there is no difference in basic and dilutive loss per share.

The Company follows the two-class method when computing net income (loss) per share, when it has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participating rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based on their respective rights to receive dividends, as if all income for the period has been distributed, or losses to be allocated if they are contractually required to fund losses. There were no amounts allocated to participating securities for the years ended December 31, 2017, 2016 and 2015, as the Company was in a loss position and had no shares that met the definition of participating securities outstanding as of December 31, 2017, 2016 and 2015.

As discussed in Note 11, “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 remained outstanding. As of December 31, 2017, no Convertible Notes remained outstanding.

The stock options 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, 2017, 2016 and 2015 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)	2017		2016		2015
Outstanding options to purchase common stock		1,616		1,903		1,921
Conversion of the Convertible Notes		—		1,216		2,500

License and Collaboration Agreements	12 Months Ended
License and Collaboration Agreements	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Agreements	5. License and Collaboration Agreements Baxalta On April 3, 2017, the Baxalta Agreement was assigned to Ipsen in connection with the completion of the Asset Sale, as discussed in Note 1, “Nature of the Business and Summary of Significant Accounting Policies.” The Company retained the rights to receive net milestone payments that may become payable pursuant to the Baxalta Agreement for the ex-U.S. development and commercialization of ONIVYDE for up to $33.0 million, which is comprised of potential payments of $18.0 million from the sale of ONIVYDE in two additional major European countries, $5.0 million related to the sale of ONIVYDE in the first major non-European, non-Asian country and $10.0 million for the first patient dosed in a pivotal clinical trial in an indication other than pancreatic cancer.

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2017

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, 2017 and 2016 and the input categories associated with those assets and liabilities:

	December 31, 2017
(in thousands)	Level 1		Level 2		Level 3
Assets:
Money market funds	$	89,310	$	—	$	—
Totals	$	89,310	$	—	$	—

	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

In December 2016, Silver Creek issued warrants to purchase an aggregate of 1.9 million shares of Silver Creek Series C preferred stock. The issuance of these warrants is described more fully in Note 11, “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.

During the first quarter of 2017, Silver Creek issued additional warrants to purchase an aggregate of 1.8 million shares of Silver Creek Series C preferred stock. During the second quarter of 2017, Silver Creek issued additional warrants to purchase an aggregate of 0.3 million shares of Silver Creek Series C preferred stock. In June 2017, Silver Creek amended the outstanding warrant purchase agreements to increase the number of shares for which each warrant is redeemable.

During the third quarter of 2017, Silver Creek completed its Series C preferred stock financing, issuing 2.0 million shares of Series C preferred stock at $1.50 per share for proceeds of $2.9 million. In conjunction with this sale, Silver Creek also issued warrants to purchase an aggregate of 1.7 million shares of Silver Creek Series C preferred stock. The sale of additional shares of Series C preferred stock in the third quarter resulted in the deconsolidation of Silver Creek, effective July 13, 2017. As such, the Company valued the warrants on that date. The warrants were valued at $5.2 million and $1.5 million as of July 13, 2017 and December 31, 2016, respectively, 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 July 14, 2017 were a risk-free interest rate of 2.1%, expected dividend yield of 0.0%, expected volatility of 60.0% and expected term of 6.4 years – 7.0 years. 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 warrants are recognized as a component of “other (expense) income, net” in the consolidated statements of operations and comprehensive income (loss). The change in fair value through the date of deconsolidation on July 13, 2017 for the year ended December 31, 2017 was $1.1 million and is recorded in other income (expense) on the statement of operations and comprehensive income (loss).

There were no changes in valuation techniques or transfers between the fair value measurement levels during the years ended December 31, 2017 or 2016. There were no liabilities measured at fair value on a recurring basis as of December 31, 2017.

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 11, “Borrowings.” No other fair value measurements were required during the year ended December 31, 2017, as the Company purchased the Convertible Notes in 2017.

As discussed in Note 11, “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. No other fair value measurements were required during the year ended December 31, 2017, as the 2022 Notes were redeemed in 2017.

- 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, 2017
Investments Debt And Equity Securities [Abstract]
Marketable Securities	7. Marketable Securities As of both December 31, 2017 and 2016, the Company maintained only cash equivalents comprised of money market funds. As of December 31, 2017, the Company did not hold any marketable securities. There were no realized gains or losses on available-for-sale securities during the years ended December 31, 2017, 2016 or 2015.

Intangible Assets, Net	12 Months Ended
Intangible Assets, Net	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Assets, Net	8. Intangible Assets, Net As part of the acquisition of Hermes BioSciences, Inc. on October 6, 2009, the Company acquired IPR&D assets of $2.8 million related to MM-302, an antibody-targeted nanotherapeutic that contains a chemotherapy drug. In December 2016, the Company determined that it would stop the ongoing Phase 2 clinical trial of MM-302, which is an antibody-targeted nanotherapeutic containing 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 income (loss). The Company did not have any intangible assets in continuing operations as of December 31, 2017 or 2016.

Property and Equipment, Net

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property and Equipment, Net

9. Property and Equipment, Net

Property and equipment, net as of December 31, 2017 and 2016 consisted of the following:

	December 31,
(in thousands)	2017			2016
Lab equipment	$	13,486		$	17,537
IT equipment		3,853			8,509
Leasehold improvements		20,790			20,633
Furniture and fixtures		335			626
Construction in process		30			378
Total property and equipment, gross		38,494			47,683
Less: Accumulated depreciation		(32,027	)		(33,471	)
Total property and equipment, net	$	6,467		$	14,212

Depreciation expense was $5.1 million, $6.5 million and $4.8 million for the years ended December 31, 2017, 2016 and 2015, respectively. Capitalized interest costs were insignificant for the years ended December 31, 2017, 2016 and 2015.

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, 2017 and 2015. During the years ended December 31, 2017 and 2016, the Company recognized a $0.4 million and less than $0.1 million gain on the sale of equipment, respectively. There were no significant gains recognized related to the sale of property and equipment during the year ended December 31, 2015.

Accounts Payable, Accrued Expenses and Other

12 Months Ended

Dec. 31, 2017

Payables And Accruals [Abstract]

Accounts Payable, Accrued Expenses and Other

10. Accounts Payable, Accrued Expenses and Other

Accounts payable, accrued expenses and other as of December 31, 2017 and 2016 consisted of the following:

	December 31,
(in thousands)	2017		2016
Accounts payable	$	2,887	$	2,692
Accrued goods and services		5,663		7,534
Accrued clinical trial costs		3,901		8,776
Accrued drug purchase costs		222		480
Accrued payroll and related benefits		2,884		3,394
Accrued restructuring expenses		628		774
Accrued interest		—		2,100
Accrued dividends payable		19		19
Silver Creek warrant liability		—		1,499
Deferred tax incentives		1,402		1,402
Total accounts payable, accrued expenses and other	$	17,606	$	28,670

Borrowings

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Borrowings

11. Borrowings

2022 Notes

In December 2015, the Company closed a private placement of $175.0 million aggregate principal amount of 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 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, 2017, 2016 and 2015, interest expense related to the 2022 Notes was approximately $6.7 million, $20.9 million, and $0.5 million, respectively. These amounts are included as a component of income from discontinued operations, net of tax in the consolidated statement of operations and comprehensive income (loss).

In connection with the completion of the Asset Sale on April 3, 2017, the liability under the 2022 Notes was satisfied. As a result of the early repayment of the 2022 Notes, a loss on extinguishment of $25.0 million was recognized in interest expense in the consolidated statement of operations and comprehensive income (loss) for the year ended December 31, 2017. The $25.0 million loss on extinguishment included a $20.1 million prepayment penalty and $4.9 million of amortization expense recognized for the remaining debt discount at settlement as a result of the early repayment.

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 14 shares of the Company’s common stock on April 18, 2016. In total, the Company issued an aggregate of 873,215 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 363,551 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 1,236,766 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 upon issuance in July 2013 was 160 shares of the Company’s common stock per $1,000 principal amount of Convertible Notes, which was equivalent to an initial conversion price of $6.25 per share of common stock. As a result of the special cash dividend that was payable on May 26, 2017 to stockholders of record as of the close of business on May 17, 2017, the conversion rate of the Convertible Notes was adjusted from 160.0000 shares of the Company’s common stock per $1,000 principal amount of Convertible Notes to 235.2112 shares of the Company’s common stock per $1,000 principal amount of Convertible Notes. As a result of the one-for-ten reverse stock split of the Company’s common stock effected on September 5, 2017, the conversion rate of the Convertible Notes was further adjusted from 235.2112 shares of the Company’s common stock per $1,000 principal amount of Convertible Notes to 23.5210 shares of the Company’s common stock per $1,000 principal amount of Convertible Notes. The conversion rate will be subject to further 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 were no events of default as of or during the years ended December 31, 2017 and 2016.

For the years ended December 31, 2017, 2016 and 2015, interest expense related to the Convertible Notes was $9.2 million, $22.7 million and $13.7 million, respectively. As discussed below, interest expense for the year ended December 31, 2017 includes a loss on extinguishment of $0.3 million associated with the October and November 2017 extinguishment as well as $3.5 million of transaction costs. 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.

In October and November 2017, the Company paid approximately $59.1 million, including $0.7 million for accrued and unpaid interest and $3.8 million of transaction costs, to purchase all of its remaining $60.8 million aggregate principal amount of outstanding Convertible Notes. The Company paid, in cash, an amount equal to $900 per $1,000 principal amount of Convertible Notes purchased, plus accrued and unpaid interest to, but not including, the date of purchase. A loss on extinguishment of $0.3 million was recognized in interest expense in the consolidated statement of operations and comprehensive income (loss) for year ended December 31, 2017. The $0.3 million loss on extinguishment represents 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 settlement, and the net carrying value of the liability. The remaining settlement consideration transferred was allocated to the reacquisition of the embedded conversion option and recognized as a $4.2 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 $3.5 million of interest expense and a $0.3 million reduction on additional paid-in capital.

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 new drug application 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 income (loss) for the year ended December 31, 2015.

For the year ended December 31, 2015, interest expense related to the Hercules loans was $5.4 million. No interest expense related to the Hercules loans was recognized during the years ended December 31, 2017 and 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 was available. If the Company borrowed under the Credit Agreement, the credit facility would have borne interest at an annual rate of 11.50%.

The Company had not borrowed any amounts under the Credit Agreement as of December 31, 2016 and, on April 27, 2017, the Credit Agreement expired.

Silver Creek Convertible Notes

In December 2012, the Company’s then-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 entered 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 convertible notes (the “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 means 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.

The Company has no future payments under any borrowings.

Restructuring Activities

12 Months Ended

Dec. 31, 2017

Restructuring And Related Activities [Abstract]

Restructuring Activities

12. 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.

Under this corporate restructuring, the Company recognized total restructuring expenses of $5.7 million for the year ended December 31, 2016, which was 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.

On January 8, 2017, the Company announced a reduction in headcount by approximately 30% in connection with the Asset Sale and the completion of its strategic pipeline review. Upon the closing of the Asset Sale and the completion of its strategic pipeline review, the Company had approximately 80 employees.

Under this corporate restructuring, the Company recognized total restructuring expenses of $9.5 million for the year ended December 31, 2017, which was related to contractual termination benefits for employees with pre-existing severance arrangements. 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 majority of these payments were made during the second quarter of 2017. The remaining payments represent severance payments that will be paid over one year. The expense of $9.5 million was included as a component of income from discontinued operations, net of tax in the consolidated statements of operations and comprehensive income (loss), as the costs are directly associated with the Asset Sale.

The following table summarizes the charges related to the restructuring activities as of December 31, 2017 and 2016:

(in thousands)

Accrued

Restructuring

Expenses at

December 31,

2016

Expenses

Less: Payments

Accrued

Restructuring

Expenses at

December 31,

2017

Severance, benefits and related costs

due to workforce reduction

774

9,521

(9,667

)

628

Totals

774

9,521

(9,667

)

628


(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	$	5,710	$	(3,565	)	$	(1,371	)	$	774
Totals	$	5,710	$	(3,565	)	$	(1,371	)	$	774

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2017
Equity [Abstract]
Common Stock	13. 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 0.4 million shares of common stock and generating approximately $38.6 million in net proceeds, after deducting commissions and offering expenses. As of December 31, 2017 and 2016, the Company had 20.0 million shares of $0.01 par value common stock authorized. There were approximately 13.3 million and 13.0 million shares of common stock issued and outstanding as of December 31, 2017 and 2016, respectively.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

14. 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 0.4 million, 0.4 million and 0.4 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, 2017, there were 0.4 million shares remaining available for grant under the 2011 Plan.

The Board of Directors authorized and declared a special cash dividend of $140.0 million on the Company's common stock, which was payable on May 26, 2017 to stockholders of record as of the close of business on May 17, 2017. The Board of Directors determined, in accordance with the adjustment provision of each of the Company’s 1999 Stock Option Plan, as amended, the 2008 Plan and the 2011 Plan (collectively, the “Equity Plans”), that the special cash dividend was unusual and non-recurring and that appropriate adjustment to the stock options to purchase shares of the Corporation’s common stock outstanding under the Equity Plans was required. The Company treated this adjustment as a modification to the original stock option grant because the terms of the agreements were modified in order to preserve the value of the option awards after a large non-recurring cash dividend. The calculation of the incremental compensation expense is based on the excess of the fair value of the award measured immediately before and after the modification. As a result, the Company recognized an incremental compensation expense of $6.9 million associated with the modification that occurred for the year ended December 31, 2017.

On August 11, 2017, the Company’s stockholders approved an amendment to the Company's certificate of incorporation to effect the Reverse Split. On September 5, 2017, the Company filed an amendment to its certificate of incorporation to effect the Reverse Split, and on September 6, 2017, the Reverse Split was effective for trading purposes. As a result of the Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock, reducing the number of issued and outstanding shares of common stock from approximately 132.8 million shares to approximately 13.28 million shares. No fractional shares were issued in connection with the Reverse Split. The amendment to the certificate of incorporation also proportionately reduced the number of authorized shares of common stock from 200 million to 20 million. The Reverse Split did not change the par value of the common stock. The Reverse Split did not change the number of authorized shares or par value of the Company’s preferred stock, of which there are no shares issued or outstanding. All outstanding stock options and Convertible Notes entitling their holders to purchase shares of common stock or acquire shares of common stock upon conversion, as the case may be, were adjusted as a result of the Reverse Split, as required by the terms of these securities.

During the years ended December 31, 2017, 2016 and 2015, the Company issued options to purchase 2.1 million, 0.4 million and 0.4 million shares of common stock, respectively. These options generally vest over a three-year period for employees. Options granted to directors generally vest immediately.

The fair value of stock options granted to employees during the years ended December 31, 2017, 2016 and 2015 was estimated at the date of grant using the following assumptions:

	Years Ended December 31,
	2017	2016	2015
Risk-free interest rate	1.7 – 2.2%	1.1 – 2.0%	1.5 – 1.8%
Expected dividend yield	0%	0%	0%
Expected term	5.0 – 6.1 years	5.0 – 5.8 years	5.0 – 5.9 years
Expected volatility	64 – 68%	67 – 69%	66 – 67%

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, 2017, 2016 and 2015 as follows:

	Years Ended December 31,
(in thousands)	2017		2016		2015
Employee awards:
Research and development expense	$	6,902	$	6,083	$	7,711
General and administrative expense		5,886		4,685		5,392
Restructuring expense		—		1,371		—
Stock-based compensation expense for employee awards		12,788		12,139		13,103
Stock-based compensation expense for non-employee awards		—		1		58
Total stock-based compensation expense	$	12,788	$	12,140	$	13,161

The following table summarizes stock option activity during the year ended December 31, 2017:

(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, 2016		1,902		$	57.70		5.97	$	7,564
Granted		2,111		$	23.69
Exercised		(323	)	$	20.70
Forfeited		(2,074	)	$	56.60
Outstanding at December 31, 2017		1,616		$	22.07		6.65	$	60,031
Vested and expected to vest at December 31, 2017		1,615		$	22.07		6.64	$	60,031
Exercisable at December 31, 2017		996		$	26.43		4.96	$	59,689

The weighted-average grant date fair value of stock options granted during the years ended December 31, 2017, 2016 and 2015 was $4.07, $58.00 and $34.10, 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, 2017, 2016 and 2015 was $2.4 million, $5.6 million and $30.9 million, respectively.

As of December 31, 2017, there was $5.0 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 2.58 years.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

15. Income Taxes

2017 U.S. Tax Reform

On December 22, 2017, President Trump signed into law the Tax Cuts and Jobs Act (the “TCJA”) that significantly reforms the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”). The TCJA, among other things, contains significant changes to corporate taxation, including reduction of the corporate tax rate from a top marginal rate of 35% to a flat rate of 21%, effective as of January 1, 2018; limitation of the tax deduction for interest expense; limitation of the deduction for net operating losses to 80% of current year taxable income and elimination of net operating loss carrybacks, in each case, for losses arising in taxable years beginning after December 31, 2017 (though any such tax losses may be carried forward indefinitely); modifying or repealing many business deductions and credits, including reducing the business tax credit for certain clinical testing expenses incurred in the testing of certain drugs for rare diseases or conditions generally referred to as “orphan drugs”; and repeal of the federal Alternative Minimum Tax (“AMT”).

The staff of the Securities and Exchange Commission issued Staff Accounting Bulletin No. 118 to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the TCJA. In connection with the initial analysis of the impact of the TCJA, the Company remeasured its deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21%. The remeasurement of the Company's deferred tax assets and liabilities was offset by a change in the valuation allowance.

The Company is still in the process of analyzing the impact to the Company of the TCJA. Where the Company has been able to make reasonable estimates of the effects related to which its analysis is not yet complete, the Company has recorded provisional amounts. The ultimate impact to the Company’s consolidated financial statements of the TCJA may differ from the provisional amounts due to, among other things, additional analysis, changes in interpretations and assumptions the Company has made, additional regulatory guidance that may be issued, and actions the Company may take as a result of the TCJA. The accounting is expected to be complete when the Company’s 2017 U.S. corporate income tax return is filed in 2018.

Income Taxes

The Company completed the Asset Sale and recorded the income tax implications of the sale in the second quarter of 2017. The Asset Sale generated taxable income for the Company, which has resulted in income tax expense. The Company released a portion of its valuation allowance in the year ended December 31, 2017, as it is now able to utilize its net operating loss carryforwards to offset the taxable income generated from the Asset Sale. The Company’s current income tax expense for the year ended December 31, 2017 is $4.2 million, which is comprised of federal AMT of $0.3 million and state income tax of $3.9 million.

Intraperiod tax allocation rules require the Company to allocate the provision for income taxes between continuing operations and other categories of earnings, such as discontinued operations. In periods in which there is pre-tax loss from continuing operations and pre-tax income in other categories of earnings, such as discontinued operations, the Company must allocate to continuing operations an income tax benefit for the loss in continuing operations with an offsetting income tax expense to discontinued operations.

For the years ended December 31, 2017, 2016 and 2015, the Company recognized an income tax benefit of $42.4 million, $13.2 million and $11.2 million, respectively, in continuing operations and income tax expense in discontinued operations of $46.6 million, $13.2 million and $11.2 million, respectively.

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

	Years Ended December 31,
	2017			2016			2015
Federal income tax at statutory federal rate		35.0	%		35.0	%		35.0	%
State taxes		1.7			0.6			1.2
Permanent differences		(3.0	)		(6.3	)		(2.4	)
Stock-based compensation		(7.2	)		(1.5	)		(1.0	)
Tax Cuts and Jobs Act impact		(19.9	)		—			—
Tax credits		11.6			12.6			9.0
Change in deferred state tax rate		7.7			(0.3	)		(1.9	)
Other		0.3			3.7			(0.5	)
Change in valuation allowance		9.9			(36.0	)		(32.5	)
Total		36.1	%		7.8	%		6.9	%

Temporary differences that give rise to significant net deferred tax assets as of December 31, 2017 and 2016 are as follows:

	December 31,
(in thousands)	2017			2016
Deferred tax assets
Net operating losses	$	43,133		$	194,027
Capitalized research and development expenses		847			15,854
Credit carryforwards		164,709			144,823
Depreciation		2,605			2,557
Deferred compensation		5,855			12,463
Accrued expenses		905			3,601
Deferred revenue		—			21,935
Other temporary differences		2,145			25,276
Installment sale tax basis		15,868			—
Total gross deferred tax assets		236,067			420,536
Valuation allowance		(236,067	)		(414,558	)
Net deferred tax assets		—			5,978
Deferred tax liabilities
Intangible assets		—			(1,428	)
Debt discount		—			(4,550	)
Net deferred taxes	$	—		$	—

At December 31, 2017, the Company had net operating loss carryforwards for federal and state income tax purposes of $138.1 million and $223.4 million, respectively. In March 2016, the FASB issued ASU No. 2016-09, “Compensation - Stock Compensation (Topic 718),” effective for annual periods beginning after December 15, 2016. The guidance changes how companies account for certain aspects of share-based payments to employees. Entities will be required to recognize income tax effects of awards in the income statement when the awards vest or are settled. In accordance with the updated guidance, the Company has increased the federal and state net operating loss carryforwards by approximately $39.2 million and $25.2 million, respectively, for the deductions related to the exercise of stock options. The Company's existing federal and state net operating loss carryforwards begin to expire 2028 through 2036. The Company also had available research and development credits for federal and state income tax purposes of approximately $28.8 million and $18.7 million, respectively. The federal and state research and development credits will begin to expire in 2022 and 2026, respectively. As of December 31, 2017, the Company also had available investment tax credits for state income tax purposes of $0.4 million, which began to expire in 2018 and will continue to expire through 2020 if they are not utilized. The Company has orphan drug credits of $120.8 million, which begin to expire in 2031.

Utilization of the net operating loss and tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of 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 tax credit carryforwards that can be utilized annually to offset future taxable income and tax. The Company completed an evaluation of ownership changes through December 31, 2017 to assess whether utilization of the Company’s net operating loss or tax credit carryforwards would be subject to an annual limitation under Section 382 of the Internal Revenue Code. The Company believes it can utilize all of its existing tax attributes as a result of the analysis. To the extent an ownership change occurs in the future, the net operating loss and tax credit carryforwards may be subject to limitation.

The Company has not, as of 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 statement of operations and comprehensive loss, balance sheet or cash flows if an adjustment were required.

In the second quarter of 2017, when the Asset Sale was consummated, the Company determined that it would utilize a portion of its deferred tax assets to offset the income generated from the Asset Sale and released a portion of its valuation allowance. As of December 31, 2017, the Company has evaluated the positive and negative evidence bearing upon the realizability of its remaining deferred tax assets, which are comprised principally of net operating loss carryforwards and research and development credits. Under the applicable accounting standards, management has considered the Company's history of losses and concluded that it is more likely than not that the Company will not recognize the benefits of its deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets. The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2017, 2016 and 2015 was as follows:

(in thousands)	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
December 31, 2015	$	257,489	$	69,088	$	—		$	326,577
December 31, 2016		326,577		87,981		—			414,558
December 31, 2017		414,558		66,801		(245,292	)		236,067

The change in the valuation allowance in in the year ended December 31, 2017 primarily relates to the release of the valuation allowance as a result of the net operating loss utilization of $217.8 million to offset the gain on the sale of the Commercial Business. The change in valuation allowance also includes a net decrease of $27.5 million related to the impact of the TCJA. Additions to the table above relate to losses generated in the current period.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

16. 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. In accordance with all related amendments, the Company leases in total approximately 112,300 square feet at its corporate headquarters located at One Kendall Square 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 June 30, 2019. 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, 2017 are $0.4 million.

In connection with the completion of the Asset Sale, on April 3, 2017, the Company entered into a sublease with Ipsen, pursuant to which Ipsen is subleasing approximately 70,237 square feet of space in the Company’s Cambridge, Massachusetts facility through the end of the term of the lease on June 30, 2019.

Total rent expense was $3.6 million, $5.0 million and $4.3 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Future minimum lease commitments on non-cancelable operating leases and scheduled sublease payments as of December 31, 2017 are as follows:

Years ended December 31,	Gross Payments		Scheduled Sublease Payments		Net Payments
2018	$	7,438	$	4,016	$	3,422
2019		3,753		2,195		1,558
Total future minimum lease payments	$	11,191	$	6,211	$	4,980

Retirement Plan	12 Months Ended
Retirement Plan	Dec. 31, 2017
Postemployment Benefits [Abstract]
Retirement Plan	18. 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, 2017, 2016 and 2015, the Company made contributions of $0.8 million, $1.3 million and $1.1 million, respectively, to the 401(k) Plan.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

19. Selected Quarterly Financial Data (Unaudited)

The following table contains quarterly financial information for 2017 and 2016. 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)
2017
Research and development expenses		21,605			19,751			13,598			12,360
General and administrative expenses		5,634			14,798			3,366			4,654
Restructuring expenses		—			—			—			—
Net loss from continuing operations		(29,206	)		(29,646	)		(5,323	)		(11,829	)
(Loss) income from discontinued operations, net of tax		(947	)		540,485			8,456			(1,122	)
Net (loss) income		(30,153	)		510,839			3,133			(12,951	)
Net (loss) income attributable to Merrimack Pharmaceuticals, Inc.		(29,686	)		511,563			3,102			(12,951	)
Basic and dilutive net (loss) income per common share
Net loss from continuing operations		(2.20	)		(2.18	)		(0.40	)		(0.89	)
Net (loss) income from discontinued operations, net of tax		(0.07	)		40.80			0.64			(0.08	)
Net (loss) income per share		(2.27	)		38.62			0.24			(0.97	)

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2016
Research and development expenses		28,002			27,695			28,247			25,621
General and administrative expenses		6,452			8,138			6,448			11,014
Restructuring expenses		—			—			809			4,901
Net loss from continuing operations		(37,715	)		(51,633	)		(26,845	)		(40,091	)
(Loss) income from discontinued operations, net of tax		(943	)		675			(3,430	)		6,464
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	)
Basic and dilutive net (loss) income per common share
Net loss from continuing operations		(3.23	)		(4.07	)		(2.06	)		(2.93	)
Net (loss) income from discontinued operations, net of tax		(0.08	)		0.05			(0.27	)		0.43
Net loss per share		(3.31	)		(4.02	)		(2.33	)		(2.50	)

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

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Segment Information

Basis of Presentation and Consolidation

Use of Estimates

Cash, Cash Equivalents and Restricted Cash

Marketable Securities

Inventory

As a result of the Asset Sale, all inventory relates to the Commercial Business and has been reclassified under discontinued operations.

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

As a result of the Asset Sale, all goodwill and intangible assets relate to the Commercial Business and have been reclassified under discontinued operations.

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

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

Income Taxes

Concentration of Credit Risk

No customer individually accounted for 10% or more of total gross revenues or total gross accounts receivable for the years ended December 31, 2017, 2016 or 2015.

Recent Accounting Pronouncements

•

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

12 Months Ended

Dec. 31, 2017

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

Discontinued Operations - Sale of Commercial Business (Tables)

12 Months Ended

Dec. 31, 2017

Discontinued Operations And Disposal Groups [Abstract]

Schedule of Discontinued Operations and Assets Held for Sale

Discontinued operations for the years ended December 31, 2017, 2016 and 2015 includes the following:

(in thousands)	Years Ended December 31,
	2017			2016			2015
Revenues:
Product revenues, net	$	16,135		$	53,064		$	4,328
License and collaboration revenues		7,797			87,119			84,930
Other revenues		1,973			4,090			—
Total revenues		25,905			144,273			89,258
Costs and expenses:
Cost of revenues		3,890			6,912			46
Research and development expenses		3,002			51,352			39,955
Selling, general and administrative expenses		10,907			48,677			33,747
Restructuring expenses		9,535			146			—
Total costs and expenses		27,334			107,087			73,748
Other income and expenses:
Interest expense		(6,743	)		(21,196	)		(463	)
Gain on sale of Commercial Business		601,670			—			—
Income from discontinued operations	$	593,498		$	15,990		$	15,047
Income tax expense		(46,626	)		(13,224	)		(11,215	)
Total income from discontinued operations	$	546,872		$	2,766		$	3,832

Schedule of Carrying Value of Assets and Liabilities Classified as Assets Held for Sale Relates to Commercial Business

The carrying value of the assets and liabilities of the Commercial Business classified as “Assets held for sale” in the consolidated balance sheets are as follows:

(in thousands)	December 31, 2016
Assets
Current assets:
Accounts receivable, net	$	17,194
Inventory		14,554
Prepaid expenses and other current assets		1,547
Total current assets held for sale		33,295
Property and equipment, net		1,553
Intangible assets, net		3,977
Goodwill		3,605
Total long-term assets held for sale		9,135
Liabilities
Current liabilities:
Accounts payable, accrued expenses and other		21,312
Deferred revenues		36,226
Total current liabilities held for sale		57,538
Deferred revenues, net of current portion		25,673
Total long-term liabilities held for sale		25,673

- Definition

Tabular disclosure of information related to a disposal group. Includes, but is not limited to, a discontinued operation, disposal classified as held-for-sale or disposed of by means other than sale or disposal of an individually significant component.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721533-107759

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 4B
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721665-107760

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1474-107760

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1361-107760

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721683-107760

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=84176398&loc=SL51724579-110230

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5C
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721675-107760

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 4A
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721663-107760

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2941-110230

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721673-107760

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721659-107760

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5A
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721671-107760

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5D
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721677-107760

+ Details

Investment in Silver Creek (Tables)

12 Months Ended

Dec. 31, 2017

Noncontrolling Interest [Abstract]

Schedule of Gain on Deconsolidation

The gain on deconsolidation includes the following:

(in thousands)
Fair value of the Company's retained investment in Silver Creek	$	11,400
Carrying value of non-controlling interest		(1,852	)
Derecognition of Silver Creek's net liabilities		1,300
Gain recognized on deconsolidation of Silver Creek	$	10,848

Schedule of Non-Controlling Interest in Subsidiary

The change in the non-controlling interest related to Silver Creek was as follows:

(in thousands)	Non- Controlling Interest
Balance at December 31, 2016	$	(1,539	)
Net loss attributable to Silver Creek through July 13, 2017		(1,160	)
Issuance of Silver Creek Series C preferred stock		847
Balance at date of deconsolidation		(1,852	)
Carrying value of non-controlling interest		1,852
Balance at December 31, 2017	$	—

(in thousands)	Non- Controlling Interest
Balance at December 31, 2015	$	239
Issuance of Silver Creek Series C preferred stock		(827	)
Net loss attributable to Silver Creek		(951	)
Balance at December 31, 2016	$	(1,539)

Net Loss Per Common Share (Tables)

12 Months Ended

Dec. 31, 2017

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)	2017		2016		2015
Outstanding options to purchase common stock		1,616		1,903		1,921
Conversion of the Convertible Notes		—		1,216		2,500

Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

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

	December 31, 2017
(in thousands)	Level 1		Level 2		Level 3
Assets:
Money market funds	$	89,310	$	—	$	—
Totals	$	89,310	$	—	$	—

	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

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net as of December 31, 2017 and 2016 consisted of the following:

	December 31,
(in thousands)	2017			2016
Lab equipment	$	13,486		$	17,537
IT equipment		3,853			8,509
Leasehold improvements		20,790			20,633
Furniture and fixtures		335			626
Construction in process		30			378
Total property and equipment, gross		38,494			47,683
Less: Accumulated depreciation		(32,027	)		(33,471	)
Total property and equipment, net	$	6,467		$	14,212

Accounts Payable, Accrued Expenses and Other (Tables)

12 Months Ended

Dec. 31, 2017

Payables And Accruals [Abstract]

Schedule of Accounts Payable, Accrued Expenses and Other

Accounts payable, accrued expenses and other as of December 31, 2017 and 2016 consisted of the following:

	December 31,
(in thousands)	2017		2016
Accounts payable	$	2,887	$	2,692
Accrued goods and services		5,663		7,534
Accrued clinical trial costs		3,901		8,776
Accrued drug purchase costs		222		480
Accrued payroll and related benefits		2,884		3,394
Accrued restructuring expenses		628		774
Accrued interest		—		2,100
Accrued dividends payable		19		19
Silver Creek warrant liability		—		1,499
Deferred tax incentives		1,402		1,402
Total accounts payable, accrued expenses and other	$	17,606	$	28,670

Restructuring Activities (Tables)

12 Months Ended

Dec. 31, 2017

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, 2017 and 2016:

(in thousands)

Accrued

Restructuring

Expenses at

December 31,

2016

Expenses

Less: Payments

Accrued

Restructuring

Expenses at

December 31,

2017

Severance, benefits and related costs

due to workforce reduction

774

9,521

(9,667

)

628

Totals

774

9,521

(9,667

)

628


(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	$	5,710	$	(3,565	)	$	(1,371	)	$	774
Totals	$	5,710	$	(3,565	)	$	(1,371	)	$	774

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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, 2017, 2016 and 2015 was estimated at the date of grant using the following assumptions:

	Years Ended December 31,
	2017	2016	2015
Risk-free interest rate	1.7 – 2.2%	1.1 – 2.0%	1.5 – 1.8%
Expected dividend yield	0%	0%	0%
Expected term	5.0 – 6.1 years	5.0 – 5.8 years	5.0 – 5.9 years
Expected volatility	64 – 68%	67 – 69%	66 – 67%

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense during the years ended December 31, 2017, 2016 and 2015 as follows:

	Years Ended December 31,
(in thousands)	2017		2016		2015
Employee awards:
Research and development expense	$	6,902	$	6,083	$	7,711
General and administrative expense		5,886		4,685		5,392
Restructuring expense		—		1,371		—
Stock-based compensation expense for employee awards		12,788		12,139		13,103
Stock-based compensation expense for non-employee awards		—		1		58
Total stock-based compensation expense	$	12,788	$	12,140	$	13,161

Summary of Stock Option Activity

The following table summarizes stock option activity during the year ended December 31, 2017:

(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, 2016		1,902		$	57.70		5.97	$	7,564
Granted		2,111		$	23.69
Exercised		(323	)	$	20.70
Forfeited		(2,074	)	$	56.60
Outstanding at December 31, 2017		1,616		$	22.07		6.65	$	60,031
Vested and expected to vest at December 31, 2017		1,615		$	22.07		6.64	$	60,031
Exercisable at December 31, 2017		996		$	26.43		4.96	$	59,689

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

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,
	2017			2016			2015
Federal income tax at statutory federal rate		35.0	%		35.0	%		35.0	%
State taxes		1.7			0.6			1.2
Permanent differences		(3.0	)		(6.3	)		(2.4	)
Stock-based compensation		(7.2	)		(1.5	)		(1.0	)
Tax Cuts and Jobs Act impact		(19.9	)		—			—
Tax credits		11.6			12.6			9.0
Change in deferred state tax rate		7.7			(0.3	)		(1.9	)
Other		0.3			3.7			(0.5	)
Change in valuation allowance		9.9			(36.0	)		(32.5	)
Total		36.1	%		7.8	%		6.9	%

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, 2017 and 2016 are as follows:

	December 31,
(in thousands)	2017			2016
Deferred tax assets
Net operating losses	$	43,133		$	194,027
Capitalized research and development expenses		847			15,854
Credit carryforwards		164,709			144,823
Depreciation		2,605			2,557
Deferred compensation		5,855			12,463
Accrued expenses		905			3,601
Deferred revenue		—			21,935
Other temporary differences		2,145			25,276
Installment sale tax basis		15,868			—
Total gross deferred tax assets		236,067			420,536
Valuation allowance		(236,067	)		(414,558	)
Net deferred tax assets		—			5,978
Deferred tax liabilities
Intangible assets		—			(1,428	)
Debt discount		—			(4,550	)
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, 2017, 2016 and 2015 was as follows:

(in thousands)	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
December 31, 2015	$	257,489	$	69,088	$	—		$	326,577
December 31, 2016		326,577		87,981		—			414,558
December 31, 2017		414,558		66,801		(245,292	)		236,067

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Commitments Under Non-cancelable Operating Leases and Scheduled Sublease Payments

Future minimum lease commitments on non-cancelable operating leases and scheduled sublease payments as of December 31, 2017 are as follows:

Years ended December 31,	Gross Payments		Scheduled Sublease Payments		Net Payments
2018	$	7,438	$	4,016	$	3,422
2019		3,753		2,195		1,558
Total future minimum lease payments	$	11,191	$	6,211	$	4,980

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2017
Research and development expenses		21,605			19,751			13,598			12,360
General and administrative expenses		5,634			14,798			3,366			4,654
Restructuring expenses		—			—			—			—
Net loss from continuing operations		(29,206	)		(29,646	)		(5,323	)		(11,829	)
(Loss) income from discontinued operations, net of tax		(947	)		540,485			8,456			(1,122	)
Net (loss) income		(30,153	)		510,839			3,133			(12,951	)
Net (loss) income attributable to Merrimack Pharmaceuticals, Inc.		(29,686	)		511,563			3,102			(12,951	)
Basic and dilutive net (loss) income per common share
Net loss from continuing operations		(2.20	)		(2.18	)		(0.40	)		(0.89	)
Net (loss) income from discontinued operations, net of tax		(0.07	)		40.80			0.64			(0.08	)
Net (loss) income per share		(2.27	)		38.62			0.24			(0.97	)

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2016
Research and development expenses		28,002			27,695			28,247			25,621
General and administrative expenses		6,452			8,138			6,448			11,014
Restructuring expenses		—			—			809			4,901
Net loss from continuing operations		(37,715	)		(51,633	)		(26,845	)		(40,091	)
(Loss) income from discontinued operations, net of tax		(943	)		675			(3,430	)		6,464
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	)
Basic and dilutive net (loss) income per common share
Net loss from continuing operations		(3.23	)		(4.07	)		(2.06	)		(2.93	)
Net (loss) income from discontinued operations, net of tax		(0.08	)		0.05			(0.27	)		0.43
Net loss per share		(3.31	)		(4.02	)		(2.33	)		(2.50	)

Nature of the Business and Summary of Significant Accounting Policies - Additional Information (Detail)			3 Months Ended								12 Months Ended
	Aug. 11, 2017 shares	Apr. 03, 2017 USD ($)	Dec. 31, 2017 USD ($) Program shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) Program Segment Customer Region shares	Dec. 31, 2016 USD ($) Customer shares	Dec. 31, 2015 USD ($) Customer	Sep. 05, 2017 shares	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of development programs active \| Program			2								2
Accumulated deficit			$ 482,771,000				$ 954,799,000				$ 482,771,000	$ 954,799,000
Net loss from continuing operations			11,829,000	$ 5,323,000	$ 29,646,000	$ 29,206,000	40,091,000	$ 26,845,000	$ 51,633,000	$ 37,715,000	76,004,000	156,284,000	$ 151,619,000
Cash in continuing operations for operating activities											104,270,000	122,935,000	109,828,000
Cash and cash equivalents			$ 93,441,000				$ 21,524,000				$ 93,441,000	$ 21,524,000	185,606,000		$ 35,688,000
Number of operating segments \| Segment											1
Number of geographic regions \| Region											1
Reverse stock split, conversion ratio	0.1
Reverse stock split description	Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock										Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock
Common stock, shares issued \| shares	132,800,000		13,343,000				13,020,000				13,343,000	13,020,000		13,280,000
Common stock, shares outstanding \| shares	132,800,000		13,343,000				13,020,000				13,343,000	13,020,000		13,280,000
Number of fractional shares issued \| shares														0
Common stock, shares authorized \| shares	200,000,000		20,000,000				20,000,000				20,000,000	20,000,000		20,000,000
Preferred stock, shares issued \| shares			0				0				0	0		0
Preferred stock, shares outstanding \| shares			0				0				0	0		0
Original maturities											Three months or less
Restricted cash			$ 800,000				$ 800,000				$ 800,000	$ 800,000
Marketable securities			0				$ 0				$ 0	0
Performance period											5 years
Tax incentive awarded											$ 3,800,000
State research and development tax credits monetized											3,400,000
Amount of tax incentives required to repay			$ 1,400,000								1,400,000
Amount of benefit recognized											$ 0	$ 100,000	$ 700,000
Customer Concentration Risk \| Sales Revenue, Net [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of customer \| Customer											0	0	0
Customer Concentration Risk \| Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of customer \| Customer											0	0	0
Maximum [Member] \| Silver Creek Pharmaceuticals Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Ownership interest (as a percent)				50.00%
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected remaining maturities period of marketable securities classified as available-for-sale											3 months
Ipsen [Member] \| Asset Sale Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Upfront cash payment received		$ 575,000,000
Working capital adjustments received		5,700,000
Ipsen [Member] \| Asset Sale Agreement [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events		450,000,000
Baxalta [Member] \| License and Collaboration Agreements [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Net milestone payments expected to be received		$ 33,000,000

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, 2017
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

Discontinued Operations - Sale of Commercial Business - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Apr. 03, 2017
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Reclassified accounts payable, accrued expenses and other from continuing operations to discontinuing operations	$ 600,000
Ipsen [Member] \| Asset Sale Agreement [Member] \| Clinical Trials in Pancreas as First-Line Treatment [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Additional payments receivable on achievement of certain milestone events		$ 225,000,000
Ipsen [Member] \| Asset Sale Agreement [Member] \| Clinical Trials in Small Cell Lung Cancer [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Additional payments receivable on achievement of certain milestone events		150,000,000
Ipsen [Member] \| Asset Sale Agreement [Member] \| Other Unrelated Clinical Trials [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Additional payments receivable on achievement of certain milestone events		75,000,000
Ipsen [Member] \| Asset Sale Agreement [Member] \| Maximum [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Additional payments receivable on achievement of certain milestone events		$ 450,000,000

Discontinued Operations - Sale of Commercial Business - Schedule of Discontinued Operations and Assets Held for Sale (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other income and expenses:
Income tax expense									$ (46,600)	$ (13,200)	$ (11,200)
Total income from discontinued operations	$ 1,122	$ (8,456)	$ (540,485)	$ 947	$ (6,464)	$ 3,430	$ (675)	$ 943	546,872	2,766	3,832
Commercial Business [Member]
Revenues:
Product revenues, net									16,135	53,064	4,328
License and collaboration revenues									7,797	87,119	84,930
Other revenues									1,973	4,090
Total revenues									25,905	144,273	89,258
Costs and expenses:
Cost of revenues									3,890	6,912	46
Research and development expenses									3,002	51,352	39,955
Selling, general and administrative expenses									10,907	48,677	33,747
Restructuring expenses									9,535	146
Total costs and expenses									27,334	107,087	73,748
Other income and expenses:
Interest expense									(6,743)	(21,196)	(463)
Gain on sale of Commercial Business									601,670
Income from discontinued operations									593,498	15,990	15,047
Income tax expense									(46,626)	(13,224)	(11,215)
Total income from discontinued operations									$ 546,872	$ 2,766	$ 3,832

Discontinued Operations - Sale of Commercial Business - Schedule of Carrying Value of Assets and Liabilities Classified as Assets Held for Sale Relates to Commercial Business (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Current assets:
Total current assets held for sale	$ 33,295
Total long-term assets held for sale	9,135
Current liabilities:
Total current liabilities held for sale	57,538
Total long-term liabilities held for sale	25,673
Commercial Business [Member]
Current assets:
Accounts receivable, net	17,194
Inventory	14,554
Prepaid expenses and other current assets	1,547
Total current assets held for sale	33,295
Property and equipment, net	1,553
Intangible assets, net	3,977
Goodwill	3,605
Total long-term assets held for sale	9,135
Current liabilities:
Accounts payable, accrued expenses and other	21,312
Deferred revenues	36,226
Total current liabilities held for sale	57,538
Deferred revenues, net of current portion	25,673
Total long-term liabilities held for sale	$ 25,673

Investment in Silver Creek - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jul. 14, 2017	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Gain on deconsolidation		$ 10,848
Equity method investment		10,551
Loss on equity method investment		(849)
Silver Creek Pharmaceuticals Inc [Member]
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Ownership interest percentage held			43.00%
Gain on deconsolidation		10,848
Investment at fair value	$ 11,400	11,400
Equity method investment		10,600
Loss on equity method investment		$ 800
Silver Creek Pharmaceuticals Inc [Member] \| Minimum [Member]
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Ownership interest percentage held by parent and its de facto agents				50.00%
Silver Creek Pharmaceuticals Inc [Member] \| Maximum [Member]
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Ownership interest percentage held by parent			50.00%

Investment in Silver Creek - Schedule of Gain on Deconsolidation (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jul. 14, 2017	Dec. 31, 2017
Minority Interest [Line Items]
Carrying value of non-controlling interest		$ (1,852)
Gain recognized on deconsolidation of Silver Creek		10,848
Silver Creek Pharmaceuticals Inc [Member]
Minority Interest [Line Items]
Fair value of the Company's retained investment in Silver Creek	$ 11,400	11,400
Carrying value of non-controlling interest		(1,852)
Derecognition of Silver Creek's net liabilities		1,300
Gain recognized on deconsolidation of Silver Creek		$ 10,848

Investment in Silver Creek - Schedule of Non-Controlling Interest in Subsidiary (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minority Interest [Line Items]
Balance at the beginning of the period	$ (1,539)	$ 239
Net loss attributable to Silver Creek	(1,160)	(1,778)	$ 170
Balance at date of deconsolidation	(1,852)
Carrying value of non-controlling interest	1,852
Balance at the end of the period		(1,539)	$ 239
Series C Preferred Stock [Member]
Minority Interest [Line Items]
Issuance of Silver Creek Series C preferred stock	847	(827)
Silver Creek [Member]
Minority Interest [Line Items]
Net loss attributable to Silver Creek	(1,160)	$ (951)
Carrying value of non-controlling interest	$ 1,852

Net Loss Per Common Share - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 31, 2013
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Amounts allocated to participating securities	$ 0	$ 0	$ 0
Participating securities outstanding, shares	0	0	0
Convertible Notes [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Aggregate principal amount				$ 125,000,000
Interest rate (as a percent)				4.50%
Aggregate principal amount of outstanding debt	$ 0	$ 60,800,000

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, 2017	Dec. 31, 2016	Dec. 31, 2015
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	1,616	1,903	1,921
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		1,216	2,500

License and Collaboration Agreements - Additional Information (Detail) - Ipsen [Member] - Asset Sale Agreement [Member]	Apr. 03, 2017 USD ($)
Development and Commercialization Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received	$ 33,000,000
Sale Milestones in Major European Countries [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	18,000,000
Sale Milestones in Major Non-European and Non-Asian Country [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	5,000,000
Clinical Trials in Lung Cancer [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	$ 10,000,000

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, 2017	Dec. 31, 2016
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	$ 89,310,000	12,373,000
Level 1 [Member] \| Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	$ 89,310,000	12,373,000
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 ($)		3 Months Ended	12 Months Ended
	Jul. 14, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 05, 2017	Jul. 13, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 22, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Preferred stock, shares issued			0	0		0
Net cash proceeds from stock issuance			$ 3,994,000	$ 3,361,000	$ 2,083,000
Transfers between fair value measurement levels			0	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%
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	2.10%			2.30%
Expected dividend yield	0.00%			0.00%
Expected volatility	60.00%			61.70%
Expected term				6 years 10 months 24 days
Change in fair value of warrant			$ 1,100,000
Silver Creek [Member] \| Minimum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Expected term	6 years 4 months 24 days
Silver Creek [Member] \| Maximum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Expected term	7 years
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		1,700,000	1,900,000	1,900,000				300,000	1,800,000
Warrants to purchase preferred stock, value				$ 1,500,000			$ 5,200,000
Preferred stock, shares issued		2,000,000
Preferred stock price per share		$ 1.50
Net cash proceeds from stock issuance		$ 2,900,000

Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost And Fair Value Debt Securities [Abstract]
Marketable securities	$ 0	$ 0
Realized gains (losses) on sale of available-for-sale securities	$ 0	$ 0	$ 0

Intangible Assets, Net - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Impairment charge			$ 2,800,000
Intangible assets, net	$ 0	$ 0	$ 0
IPR&D [Member]
Business Acquisition [Line Items]
Impairment charge	$ 2,800,000
Hermes BioSciences, Inc. [Member]
Business Acquisition [Line Items]
Acquired IPR&D assets recognized in a business combination		$ 2,800,000
Acquisition date		Oct. 06, 2009

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 38,494	$ 47,683
Less: Accumulated depreciation	(32,027)	(33,471)
Total property and equipment, net	6,467	14,212
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	13,486	17,537
IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	3,853	8,509
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	20,790	20,633
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	335	626
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 30	$ 378

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 5,100	$ 6,500	$ 4,800
Charge related to disposal of property and equipment		493	$ 4
Gain on sale of property and equipment	$ 439	40
Maximum [Member]
Property, Plant and Equipment [Line Items]
Gain on sale of property and equipment		$ 100

Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts Payable And Accrued Liabilities [Line Items]
Accounts payable	$ 2,887	$ 2,692
Accrued goods and services	5,663	7,534
Accrued clinical trial costs	3,901	8,776
Accrued drug purchase costs	222	480
Accrued payroll and related benefits	2,884	3,394
Accrued restructuring expenses	628	774
Accrued interest		2,100
Accrued dividends payable	19	19
Deferred tax incentives	1,402	1,402
Total accounts payable, accrued expenses and other	$ 17,606	28,670
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. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Debt maturity date		Jul. 15, 2020
Interest expense		$ 34,650,000	$ 22,449,000	$ 18,769,000
Loss on extinguishment of debt		$ 5,202,000	14,566,000
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			175,000,000
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		$ 6,700,000	$ 20,900,000	$ 500,000
Loss on extinguishment of debt		25,000,000
Prepayment penalty of extinguishment of debt		20,100,000
Amortization expense recognized for remaining debt discount at settlement		4,900,000
2022 Notes [Member] \| Interest Expense [Member]
Debt Instrument [Line Items]
Loss on extinguishment of debt		$ 25,000,000
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	2 Months Ended	3 Months Ended	12 Months Ended
	Sep. 05, 2017 shares	Aug. 11, 2017 shares	May 26, 2017	Apr. 18, 2016 shares	Apr. 13, 2016 USD ($) shares	Jul. 31, 2013 USD ($) $ / shares	Jul. 31, 2013 USD ($) $ / shares	Nov. 30, 2017 USD ($) $ / shares	Jun. 30, 2016 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
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	13,280,000	132,800,000								13,343,000	13,020,000
Loss on extinguishment of debt										$ 5,202,000	$ 14,566,000
Debt maturity date										Jul. 15, 2020
Reverse stock split description		Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock								Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock
Reverse stock split, conversion ratio		0.1
Interest expense										$ 34,650,000	22,449,000	$ 18,769,000
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	23.5210		235.2112	14		160
Common stock, shares issued \| shares				873,215	363,551				1,236,766
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	300,000
Reduction in additional paid-in capital attributable to embedded conversion option									39,800,000	$ 4,200,000
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
Reverse stock split description										one-for-ten reverse stock split
Reverse stock split, conversion ratio	0.1
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										$ 9,200,000	$ 22,700,000	$ 13,700,000
Debt instrument, transaction costs								$ 3,800,000		3,500,000
Repayment of debt								59,100,000
Accrued and unpaid interest								700,000
Purchase of convertible notes								$ 60,800,000
Offering amount of per unit debt instrument issued at discount \| $ / shares								900
Principal amount of per unit debt instrument issued at discount \| $ / shares								1,000
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	300,000
Convertible Notes [Member] \| Interest Expense [Member]
Debt Instrument [Line Items]
Loss on extinguishment of debt										300,000
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	$ 3,500,000

Borrowings - Loan Agreement - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 25, 2015	Nov. 06, 2014	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	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					$ 34,650,000	$ 22,449,000	$ 18,769,000
2022 Notes [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount of loan			$ 175,000,000	175,000,000			175,000,000
Debt issuance costs			900,000
Interest expense					6,700,000	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			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	$ 0	5,400,000
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 of loan	$ 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
	Dec. 31, 2017	Dec. 31, 2016	Nov. 08, 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, annual interest rate			11.50%
Credit facility, amounts borrowed		$ 0
Credit facility, expiration date	Apr. 27, 2017

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Borrowings - Silver Creek Convertible Notes - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended	12 Months Ended
	Dec. 31, 2016	May 31, 2016	Dec. 31, 2012	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Sep. 05, 2017	Jun. 30, 2017	Mar. 31, 2017	Aug. 31, 2016
Debt Instrument [Line Items]
Preferred stock issued	0				0	0				0
Proceeds from sale of preferred stock					$ 3,994,000	$ 3,361,000	$ 2,083,000
Silver Creek Pharmaceuticals Inc [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 Pharmaceuticals Inc [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 Pharmaceuticals Inc [Member] \| Silver Creek Series C Preferred Stock [Member]
Debt Instrument [Line Items]
Preferred stock issued				2,000,000
Preferred stock price per share				$ 1.50
Warrants to purchase	1,900,000			1,700,000	1,900,000	1,900,000					300,000	1,800,000
Proceeds from sale of preferred stock				$ 2,900,000
Silver Creek Pharmaceuticals Inc [Member] \| Silver Creek Series C Preferred Stock [Member] \| Milestone Event 1 [Member]
Debt Instrument [Line Items]
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.
Number of warrants exercisable					1,200,000
Silver Creek Pharmaceuticals Inc [Member] \| Silver Creek Series C Preferred Stock [Member] \| Milestone Event 2 [Member]
Debt Instrument [Line Items]
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 means the date that is seven business days following the first dose in humans in a clinical trial
Number of warrants exercisable					700,000
Silver Creek Pharmaceuticals Inc [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
Silver Creek Pharmaceuticals Inc [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
Silver Creek Pharmaceuticals Inc [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
Silver Creek Pharmaceuticals Inc [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
Silver Creek Pharmaceuticals Inc [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	1,500,000					1,500,000
Preferred stock price per share	$ 1.50					$ 1.50
Debt conversion, shares issued	800,000
Silver Creek Pharmaceuticals Inc [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 Pharmaceuticals Inc [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%
Discount on automatic conversion into the next qualifying equity financing (as a percent)			25.00%
Derivative liability			$ 200,000
Silver Creek Convertible Note [Member] \| Silver Creek Pharmaceuticals Inc [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

Restructuring Activities - Additional Information (Detail) $ in Thousands			3 Months Ended		12 Months Ended
	Jan. 08, 2017 Employee	Oct. 03, 2016	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Restructuring Cost And Reserve [Line Items]
Reduction in headcount, percent		22.00%
Restructuring activity, announcement date					Oct. 03, 2016
Restructuring expenses			$ 4,901	$ 809	$ 9,521	$ 5,710
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.
January 2017 Corporate Restructuring [Member]
Restructuring Cost And Reserve [Line Items]
Reduction in headcount, percent	30.00%
Restructuring activity, announcement date					Jan. 08, 2017
Restructuring and related cost, number of expected employees after headcount reduction \| Employee	80
January 2017 Corporate Restructuring [Member] \| Discontinued Operations [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses					$ 9,500
Stock-based Compensation Expense, Contractual Termination Benefits and One-time Employee Termination Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses						$ 5,700
Contractual Termination Benefits [Member] \| January 2017 Corporate Restructuring [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses					$ 9,500
One-time Termination Benefits \| January 2017 Corporate Restructuring [Member]
Restructuring Cost And Reserve [Line Items]
Severance payments payment period					1 year

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, 2017	Dec. 31, 2016
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses			$ 774
Expenses	$ 4,901	$ 809	9,521	$ 5,710
Less: Payments			(9,667)	(3,565)
Less: Non-Cash Expenses				(1,371)
Accrued Restructuring Expenses	774		628	774
Severance Benefits and Related Costs Due to Workforce Reduction [Member]
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses			774
Expenses			9,521	5,710
Less: Payments			(9,667)	(3,565)
Less: Non-Cash Expenses				(1,371)
Accrued Restructuring Expenses	$ 774		$ 628	$ 774

Common Stock - Additional Information (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Jul. 13, 2015	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2017	Sep. 05, 2017	Aug. 11, 2017	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				13,343,000	13,280,000	132,800,000	13,020,000
Common stock, shares authorized				20,000,000	20,000,000	200,000,000	20,000,000
Common stock, par value				$ 0.01			$ 0.01
Common stock, shares outstanding				13,343,000	13,280,000	132,800,000	13,020,000
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		400,000
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) $ / shares in Units, $ in Millions		1 Months Ended			12 Months Ended
	Aug. 11, 2017 shares	Feb. 29, 2016 shares	Feb. 28, 2015 shares	Mar. 31, 2014 shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 05, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Special cash dividend paid \| $					$ 140.0
Dividend payable date					May 26, 2017
Dividend payable, date of record					May 17, 2017
Incremental compensation expense \| $					$ 6.9
Reverse stock split description	Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock				Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock
Reverse stock split, conversion ratio	0.1
Common stock, shares issued	132,800,000				13,343,000	13,020,000		13,280,000
Common stock, shares outstanding	132,800,000				13,343,000	13,020,000		13,280,000
Common stock, shares authorized	200,000,000				20,000,000	20,000,000		20,000,000
Number of fractional shares issued								0
Preferred stock, shares issued					0	0		0
Preferred stock, shares outstanding					0	0		0
Number of Options, Granted					2,111,000
Weighted-average grant date fair value per share of stock options \| $ / shares					$ 4.07	$ 58.00	$ 34.10
Aggregate intrinsic value of options exercised \| $					$ 2.4	$ 5.6	$ 30.9
Unrecognized stock-based compensation expense related to nonvested stock options \| $					$ 5.0
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized					2 years 6 months 29 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)		400,000	400,000	400,000
Shares of common stock available for grant (in shares)					400,000
Number of Options, Granted					2,100,000	400,000	400,000
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, 2017	Dec. 31, 2016	Dec. 31, 2015
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	1.70%	1.10%	1.50%
Expected volatility	64.00%	67.00%	66.00%
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	2.20%	2.00%	1.80%
Expected volatility	68.00%	69.00%	67.00%
Expected term	6 years 1 month 6 days	5 years 9 months 18 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, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 12,788	$ 12,139	$ 13,103
Stock-based compensation expense for non-employee awards		1	58
Total stock-based compensation expense	12,788	12,140	13,161
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	6,902	6,083	7,711
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	$ 5,886	4,685	$ 5,392
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, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Options, Outstanding, Beginning balance	1,902
Number of Options, Granted	2,111
Number of Options, Exercised	(323)
Number of Options, Forfeited	(2,074)
Number of Options, Outstanding, Ending balance	1,616	1,902
Number of Options, Vested and expected to vest	1,615
Number of Options, Exercisable	996
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 57.70
Weighted-Average Exercise Price, Granted	23.69
Weighted-Average Exercise Price, Exercised	20.70
Weighted-Average Exercise Price, Forfeited	56.60
Weighted-Average Exercise Price, Outstanding, Ending balance	22.07	$ 57.70
Weighted-Average Exercise Price, Vested and expected to vest	22.07
Weighted-Average Exercise Price, Exercisable	$ 26.43
Weighted-Average Remaining Contractual Term	6 years 7 months 24 days	5 years 11 months 19 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	6 years 7 months 20 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 11 months 15 days
Aggregate Intrinsic Value, Outstanding	$ 60,031	$ 7,564
Aggregate Intrinsic Value, Vested and expected to vest	60,031
Aggregate Intrinsic Value, Exercisable	$ 59,689

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Current Income tax expense			$ 4,200
Current federal AMT Income tax expense			300
Current state Income tax expense			$ 3,900
Corporate tax rate			35.00%	35.00%	35.00%
Tax cuts and jobs act of 2017, accounting complete	false
Tax cuts and jobs act of 2017 percentage of tax deduction for interest expense and net operating losses of current year taxable income			80.00%
Income tax benefit			$ 42,399	$ 13,224	$ 11,215
Income tax expense (benefit) in discontinued operations			46,600	$ 13,200	$ 11,200
Federal Orphan Drug Credits			$ 120,800
Federal orphan drug credits begin to expire			2031
Change in valuation allowance			$ 217,800
Tax cuts and jobs act of 2017 incomplete accounting change in valuation allowance net decrease			27,500
ASU No. 2016-09 [Member]
Operating Loss Carryforwards [Line Items]
Federal and state net operating loss carryforwards relate to deductions for stock option compensation			39,200
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			$ 223,400
Net operating loss carryforwards expire year begin			2028
Net operating loss carryforwards expire year through			2036
State [Member] \| Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward			$ 18,700
Tax credit carryforwards expire year begin			2022
Tax credit carryforwards expire year through			2026
State [Member] \| Investment [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward			$ 400
Tax credit carryforwards expire year begin			2018
Tax credit carryforwards expire year through			2020
State [Member] \| ASU No. 2016-09 [Member]
Operating Loss Carryforwards [Line Items]
Federal and state net operating loss carryforwards relate to deductions for stock option compensation			$ 25,200
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			$ 138,100
Net operating loss carryforwards expire year begin			2028
Net operating loss carryforwards expire year through			2036
Federal [Member] \| Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward			$ 28,800
Tax credit carryforwards expire year begin			2022
Tax credit carryforwards expire year through			2026
Scenario, Plan [Member]
Operating Loss Carryforwards [Line Items]
Corporate tax rate		21.00%

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, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal income tax at statutory federal rate	35.00%	35.00%	35.00%
State taxes	1.70%	0.60%	1.20%
Permanent differences	(3.00%)	(6.30%)	(2.40%)
Stock-based compensation	(7.20%)	(1.50%)	(1.00%)
Tax Cuts and Jobs Act impact	(19.90%)
Tax credits	11.60%	12.60%	9.00%
Change in deferred state tax rate	7.70%	(0.30%)	(1.90%)
Other	0.30%	3.70%	(0.50%)
Change in valuation allowance	9.90%	(36.00%)	(32.50%)
Total	36.10%	7.80%	6.90%

Income Taxes - Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets
Net operating losses	$ 43,133	$ 194,027
Capitalized research and development expenses	847	15,854
Credit carryforwards	164,709	144,823
Depreciation	2,605	2,557
Deferred compensation	5,855	12,463
Accrued expenses	905	3,601
Deferred revenue		21,935
Other temporary differences	2,145	25,276
Installment sale tax basis	15,868
Total gross deferred tax assets	236,067	420,536
Valuation allowance	$ (236,067)	(414,558)	$ (326,577)	$ (257,489)
Net deferred tax assets		5,978
Deferred tax liabilities
Intangible assets		(1,428)
Debt discount		$ (4,550)

Income Taxes - Schedule of Changes in the Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 414,558	$ 326,577	$ 257,489
Additions	66,801	87,981	69,088
Deductions	(245,292)
Balance at end of period	$ 236,067	$ 414,558	$ 326,577

Commitments and Contingencies - Additional Information (Detail) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2016 ft²	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Apr. 03, 2017 ft²
Operating Leased Assets [Line Items]
Amended lease termination date		Jun. 30, 2019
Aggregate space that the entity will lease under the amended lease agreement \| ft²		112,300
Aggregate landlord reimbursable tenant improvements received under the existing lease and the lease amendment \| $			$ 9.5
Sublease Agreement [Member]
Operating Leased Assets [Line Items]
Area of office and lab \| ft²	8,143
Lease expiration date	Jun. 30, 2019
Operating leases, future minimum rental payments receivable \| $		$ 0.4
Total rent expense \| $		$ 3.6	$ 5.0	$ 4.3
Sublease Agreement [Member] \| Ipsen [Member]
Operating Leased Assets [Line Items]
Area of sublease property \| ft²					70,237

Commitments and Contingencies - Schedule of Future Minimum Lease Commitments Under Non-cancelable Operating Leases and Scheduled Sublease Payments (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Gross Payments, 2018	$ 7,438
Gross Payments, 2019	3,753
Gross Payments, Total future minimum lease payments	11,191
Scheduled Sublease Payments, 2018	4,016
Scheduled Sublease Payments, 2019	2,195
Scheduled Sublease Payments, Total future minimum lease payments	6,211
Net Payments, 2018	3,422
Net Payments, 2019	1,558
Net Payments, Total future minimum lease payments	$ 4,980

Related Party Transactions - Additional Information (Detail) - shares	Dec. 31, 2017	Sep. 05, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Preferred stock issued	0	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)	4.00%		7.00%	7.00%
Silver Creek [Member] \| Series C Preferred Stock [Member]
Related Party Transaction [Line Items]
Preferred stock issued	0		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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Research and development expenses	$ 12,360	$ 13,598	$ 19,751	$ 21,605	$ 25,621	$ 28,247	$ 27,695	$ 28,002	$ 67,314	$ 109,565	$ 121,033
General and administrative expenses	4,654	3,366	14,798	5,634	11,014	6,448	8,138	6,452	28,452	32,052	24,048
Restructuring expenses					4,901	809			9,521	5,710
Loss from continuing operations	(11,829)	(5,323)	(29,646)	(29,206)	(40,091)	(26,845)	(51,633)	(37,715)	(76,004)	(156,284)	(151,619)
(Loss) income from discontinued operations, net of tax	(1,122)	8,456	540,485	(947)	6,464	(3,430)	675	(943)	(546,872)	(2,766)	(3,832)
Net (loss) income	(12,951)	3,133	510,839	(30,153)	(33,627)	(30,275)	(50,958)	(38,658)	470,868	(153,518)	(147,787)
Net (loss) income attributable to Merrimack Pharmaceuticals, Inc.	$ (12,951)	$ 3,102	$ 511,563	$ (29,686)	$ (32,449)	$ (30,068)	$ (50,750)	$ (38,473)	$ 472,028	$ (151,740)	$ (147,957)
Basic and dilutive net income (loss) per common share
Net loss from continuing operations	$ (0.89)	$ (0.40)	$ (2.18)	$ (2.20)	$ (2.93)	$ (2.06)	$ (4.07)	$ (3.23)	$ (5.66)	$ (12.33)	$ (13.63)
Net (loss) income from discontinued operations, net of tax	(0.08)	0.64	40.80	(0.07)	0.43	(0.27)	0.05	(0.08)	41.33	0.22	0.34
Net (loss) income per share	$ (0.97)	$ 0.24	$ 38.62	$ (2.27)	$ (2.50)	$ (2.33)	$ (4.02)	$ (3.31)	$ 35.67	$ (12.11)	$ (13.29)

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	17. Related Party Transactions Related parties of the Company held approximately 4%, 7% and 7% of the outstanding shares of Silver Creek Series A and Series B preferred stock as of December 31, 2017, 2016 and 2015, respectively. No shares of Silver Creek Series C preferred stock issued during 2017 or 2016 were held by related parties of the Company as of December 31, 2017, 2016 or 2015.