Merrimack Pharmaceuticals (MACK) 8-K 15 Dec 17 Other Events Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2016
Document And Entity Information [Abstract]
Document Type	8-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Trading Symbol	MACK
Entity Registrant Name	MERRIMACK PHARMACEUTICALS INC
Entity Central Index Key	1,274,792

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 21,524,000	$ 185,606,000
Restricted cash	102,000	101,000
Accounts receivable, net	275,000	11,000
Prepaid expenses and other current assets	2,239,000	4,214,000
Assets held for sale	33,295,000	11,462,000
Total current assets	57,435,000	201,394,000
Restricted cash	674,000	584,000
Property and equipment, net	14,212,000	20,101,000
Other assets	27,000	27,000
Intangible assets, net	0	2,800,000
Long-term assets held for sale	9,135,000	9,974,000
Total assets	81,483,000	234,880,000
Current liabilities:
Accounts payable, accrued expenses and other	28,670,000	36,739,000
Deferred rent	2,014,000	1,527,000
Liabilities held for sale	57,538,000	65,480,000
Total current liabilities	88,222,000	103,746,000
Deferred rent, net of current portion	3,386,000	4,926,000
Deferred tax incentives, net of current portion		1,045,000
Long-term debt, net of current portion	216,861,000	257,655,000
Long-term liabilities held for sale	25,673,000	51,197,000
Total liabilities	334,142,000	418,569,000
Commitments and contingencies
Non-controlling interest	(1,539,000)	239,000
Stockholders’ deficit:
Preferred stock, $0.01 par value: 10,000 shares authorized at December 31, 2016 and 2015; no shares issued or outstanding at December 31, 2016 or 2015
Common stock, $0.01 par value: 20,000 shares authorized at December 31, 2016 and 2015, 13,020 and 11,587 issued and outstanding at December 31, 2016 and 2015, respectively	1,302,000	1,159,000
Additional paid-in capital	702,377,000	617,145,000
Accumulated deficit	(954,799,000)	(802,232,000)
Total stockholders’ deficit	(251,120,000)	(183,928,000)
Total liabilities, non-controlling interest and stockholders’ deficit	$ 81,483,000	$ 234,880,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	13,020,000	11,587,000
Common stock, shares outstanding	13,020,000	11,587,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenues			$ 92,296
Costs and expenses:
Research and development expenses	$ 109,565	$ 121,033	103,310
General and administrative expenses	32,052	24,048	18,766
Restructuring expenses	5,710
Total costs and expenses	147,327	145,081	122,076
Loss from continuing operations	(147,327)	(145,081)	(29,780)
Other income and expenses:
Interest income	276	99	114
Interest expense	(22,449)	(18,769)	(18,230)
Other (expense) income, net	(8)	917	813
Net loss from continuing operations before income tax benefit	(169,508)	(162,834)	(47,083)
Income tax benefit	13,224	11,215
Net loss from continuing operations	(156,284)	(151,619)	(47,083)
Discontinued operations:
Income (loss) from discontinued operations, net of tax	2,766	3,832	(36,476)
Net loss	(153,518)	(147,787)	(83,559)
Net income (loss) attributable to non-controlling interest	(1,778)	170	(268)
Net loss attributable to Merrimack Pharmaceuticals, Inc.	(151,740)	(147,957)	(83,291)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities		74	(50)
Other comprehensive income (loss)		74	(50)
Comprehensive loss	(151,740)	(147,883)	(83,341)
Amounts attributable to Merrimack Pharmaceuticals, Inc.:
Net loss from continuing operations	(154,506)	(151,789)	(46,815)
Income (loss) from discontinued operations, net of tax	2,766	3,832	(36,476)
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$ (151,740)	$ (147,957)	$ (83,291)
Basic and dilutive net income (loss) per common share
Net loss from continuing operations	$ (12.33)	$ (13.63)	$ (4.49)
Net income (loss) from discontinued operations, net of tax	0.22	0.34	(3.49)
Net loss per share	$ (12.11)	$ (13.29)	$ (7.98)
Weighted-average common shares used per share calculations—basic and diluted	12,533	11,136	10,441

Consolidated Statements of Non-

Consolidated Statements of Non-Controlling Interest and Stockholders' Deficit - USD ($) shares in Thousands, $ in Thousands	Total	Silver Creek Series B Preferred Stock [Member]	Silver Creek Series C Preferred Stock [Member]	Convertible Notes [Member]	Silver Creek [Member]	Silver Creek [Member]Silver Creek Series B Preferred Stock [Member]	Silver Creek [Member]Silver Creek Series C Preferred Stock [Member]	Non-Controlling Interest [Member]	Non-Controlling Interest [Member]Silver Creek Series B Preferred Stock [Member]	Non-Controlling Interest [Member]Silver Creek Series C Preferred Stock [Member]	Non-Controlling Interest [Member]Silver Creek [Member]	Common Stock [Member]	Common Stock [Member]Convertible Notes [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]Silver Creek Series B Preferred Stock [Member]	Additional Paid-In Capital [Member]Silver Creek Series C Preferred Stock [Member]	Additional Paid-In Capital [Member]Convertible Notes [Member]	Additional Paid-In Capital [Member]Silver Creek [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2013	$ (43,465)							$ 337				$ 1,025		$ 527,779					$ (24)	$ (572,245)
Balance (in shares) at Dec. 31, 2013												10,252
Exercise of stock options and common stock warrants	10,425											$ 42		10,383
Exercise of stock options and common stock warrants (shares)												418
Issuance of stock due to conversion of convertible notes					$ 678						$ 366							$ 678
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.					$ 400
Stock-based compensation	13,197													13,197
Other comprehensive income (loss)	(50)																		(50)
Loss attributable to non-controlling interest	634							(634)												634
Net loss	(83,559)																			(83,559)
Balance at Dec. 31, 2014	(102,140)							69				$ 1,067		552,037					(74)	(655,170)
Balance (in shares) at Dec. 31, 2014												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				$ 900			$ 895						$ 1,188
Stock-based compensation	15,351													15,351
Other comprehensive income (loss)	74																		$ 74
Loss attributable to non-controlling interest	725							(725)												725
Net loss	(147,787)																			(147,787)
Balance at Dec. 31, 2015	(183,928)							239				$ 1,159		617,145						(802,232)
Balance (in shares) at Dec. 31, 2015												11,587
Exercise of stock options	$ 6,442											$ 20		6,422
Exercise of stock options (shares)	196											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 of convertible notes due 2020	$ (39,923)													(39,923)
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.			$ 2,689				$ (800)			$ (827)						$ 2,689
Stock-based compensation	15,206													15,206
Loss attributable to non-controlling interest	951							(951)												951
Net loss	(153,518)																			(153,518)
Balance at Dec. 31, 2016	$ (251,120)							$ (1,539)				$ 1,302		$ 702,377						$ (954,799)
Balance (in shares) at Dec. 31, 2016												13,020

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net loss	$ (153,518)	$ (147,787)	$ (83,559)
Income (loss) from discontinued operations, net of tax	2,766	3,832	(36,476)
Loss from continuing operations	(156,284)	(151,619)	(47,083)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense	6,004	8,217	8,511
Non-cash loss on extinguishment of convertible notes due 2020	14,566
Non-cash activity related to discontinued operations	13,224	11,215
Benefit from intra period tax allocation	(13,224)	(11,215)
Loss on disposal of property and equipment	493	4
Gain on sale of property and equipment	(40)
Impairment of in-process research and development intangible asset	2,800
Depreciation and amortization expense	4,895	3,250	2,438
Stock-based compensation expense	12,140	13,161	11,978
Purchased premiums and interest on marketable securities			858
Changes in operating assets and liabilities:
Accounts receivable	(264)	1,654	4,235
Prepaid expenses and other current assets	2,184	(32)	1,093
Accounts payable, accrued expenses and other	(9,837)	13,163	(5,641)
Deferred revenues			(73,392)
Deferred rent and tax incentives	408	2,374	712
Net cash used in continuing operations for operating activities	(122,935)	(109,828)	(96,291)
Net cash provided by (used in) discontinuing operations for operating activities	(47,306)	4,472	61,483
Net cash used in operating activities	(170,241)	(105,356)	(34,808)
Cash flows from investing activities
Purchase of marketable securities	(84,262)		(111,832)
Proceeds from sales and maturities of marketable securities	84,160	87,899	111,858
Purchase of property and equipment	(2,640)	(11,902)	(4,538)
Other investing activities, net			(2)
Net cash provided by (used in) continuing operations for investing activities	(2,742)	75,997	(4,514)
Net cash used in discontinuing operations for investing activities	(515)	(887)	(1,497)
Net cash provided by (used in) investing activities	(3,257)	75,110	(6,011)
Cash flows from financing activities
Proceeds from exercise of options and warrants to purchase common stock	6,224	10,087	10,384
Proceeds from issuance of convertible promissory notes by Silver Creek Pharmaceuticals, Inc.			1,044
Proceeds from at the market offering, net of issuance costs		38,560
Proceeds from issuance of senior secured notes due 2022, net of issuance costs		169,434
Proceeds from issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.	3,361	2,083
Repayment of loans payable to Hercules Technology Growth Capital, Inc.		(40,000)
Other financing activities, net	(169)		(7)
Net cash provided by financing activities	9,416	180,164	11,421
Net increase (decrease) in cash and cash equivalents	(164,082)	149,918	(29,398)
Cash and cash equivalents, beginning of period	185,606	35,688	65,086
Cash and cash equivalents, end of period	21,524	185,606	35,688
Non-cash investing and financing activities
Purchases of property and equipment in accounts payable, accrued expenses and other	130	816	704
Receivables related to stock option exercises in prepaid expenses and other current assets	232	14
Receivables related to the sale of property and equipment in prepaid expenses and other current assets	40
Principal amount of convertible notes	64,209
Supplemental disclosure of cash flows
Cash paid for interest	23,914	10,087	9,510
Silver Creek [Member]
Cash flows from financing activities
Cash and cash equivalents, beginning of period	700
Cash and cash equivalents, end of period	$ 1,900	$ 700
Silver Creek [Member] | Series A Preferred Stock [Member]
Non-cash investing and financing activities
Principal amount of convertible notes			$ 1,044

Nature of the Business and Summ

Nature of the Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Nature of the Business and Summary of Significant Accounting Policies	1. Nature of the Business and Summary of Significant Accounting Policies Nature of the Business Merrimack Pharmaceuticals, Inc. (the “Company”) is a biopharmaceutical company based in Cambridge, Massachusetts that is outthinking cancer to ensure that 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 studies in distinct indications and six candidates in preclinical development, fit into the Company’s strategy of (1) understanding the biological problems the Company is trying to solve, (2) designing specific solutions 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’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 as of the date of the Company’s most recent Quarterly Report on Form 10-Q are as follows: • MM-121 (seribantumab), 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 Phase 2 randomized SHERLOC clinical trial, evaluating MM-121 in patients with heregulin positive non-small cell adenocarcinoma of the lung in combination with docetaxel. The Company has also initiated trial sites for the Phase 2 randomized SHERBOC clinical trial in patients with heregulin positive, hormone receptor positive, ErbB2 (HER2) negative, metastatic breast cancer in combination with fulvestrant, and expects to dose the first patient in the SHERBOC clinical trial in the fourth quarter of 2017; • MM-141 (istiratumab), a fully human bispecific tetravalent monoclonal 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 receptors. The Company is currently conducting and has completed enrollment of the Phase 2 randomized CARRIE clinical trial evaluating MM-141 in previously untreated metastatic pancreatic cancer patients with high levels of free IGF-1 in combination with nab-paclitaxel and gemcitabine; and • MM-310, an antibody-directed nanotherapeutic (“ADN”) that contains a novel prodrug of the highly potent chemotherapy docetaxel and targets the ephrin receptor A2 (“EphA2”) receptor, which is highly expressed in most solid tumor types. MM-310 was designed to improve the therapeutic window of docetaxel in major oncology indications, 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 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 has incurred significant expenses and operating losses to date, and it expects to continue to incur significant expenses and operating losses for at least the next several years. In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern As of December 31, 2016, the Company had $21.5 million in unrestricted cash and cash equivalents, had suffered recurring losses from operations and had negative working capital and cash outflows from operating activities. Based on the evaluation completed in connection with the filing of the Company’s Annual Report on Form 10-K for the year ended December 31, 2016, including consideration of management’s plans, the Company previously concluded that there was substantial doubt as to its ability to continue as a going concern within one year after March 1, 2017, the date that the consolidated financial statements were issued. On April 3, 2017, the Company closed the Asset Sale with Ipsen and received a $575.0 million upfront cash payment (subject to a working capital adjustment). The Company used a portion of the cash payment to redeem the $175.0 million outstanding aggregate principal amount of 11.50% senior secured notes due 2022 (the “2022 Notes”), which also required an additional make-whole premium payment of approximately $20.1 million, and deposited $60.0 million into an escrow account in response to a lawsuit filed by the trustee and certain holders of its 4.50% convertible notes due 2020 (the “Convertible Notes”). The Company also distributed $140.0 million of the upfront cash payment in the form of a special cash dividend to stockholders. After consideration of the Company’s cash and cash equivalents balance at December 31, 2016 and the net proceeds from the Asset Sale, the Company has concluded that the previous conditions and events that raised substantial doubt about its ability to continue as a going concern have been alleviated. As of December 15, 2017, the re-issuance date of the consolidated financial statements for the year ended December 31, 2016, the Company expects that its cash and cash equivalents will be sufficient to fund its operating expenses and capital expenditure requirements through the second quarter of 2019. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations. The Company may seek additional funding through public or private debt or equity financings, through existing or new collaboration arrangements, or through divestitures of its assets. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into additional collaborative arrangements or divest its assets. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Arrangements with collaborators or others may require the Company to relinquish rights to certain of its technologies or product candidates. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate its research and development programs or commercialization efforts, which could adversely affect its business prospects. Summary of Significant Accounting Policies The 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. Basis of Presentation and Consolidation The accompanying consolidated financial statements have been prepared under U.S. generally accepted accounting principles (“GAAP”) and include the accounts of the Company and its wholly owned subsidiary, Merrimack Pharmaceuticals (Bermuda) Ltd., which was merged with and into the Company during the third quarter of 2014. The Company also consolidates its majority owned subsidiary, Silver Creek Pharmaceuticals, Inc. (“Silver Creek”). All intercompany transactions and balances have been eliminated in consolidation. 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 a loss from discontinued operations, net of tax in the condensed consolidated statements of operations for all periods presented. In addition, in the condensed consolidated balance sheet as of December 31, 2016, 2015 and 2014, the assets and liabilities held for sale have been presented separately. For additional information, see Note 2, “Discontinued Operations.” 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 the 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 15, “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, including the estimated percentage of billable expenses in any particular budget period, periods of meaningful use of licensed products, estimated service periods and services to be completed under a collaboration, estimates used in accounting for revenue separability and recognition, estimates of discounts and allowances related to commercial sales of ONIVYDE, estimates utilized in the valuation of inventory, useful lives with respect to long-lived assets and intangible assets, accounting for stock-based compensation, contingencies, intangible assets, goodwill, in-process research and development (“IPR&D”), tax valuation reserves and accrued expenses. The Company’s actual results may differ from these estimates under different assumptions or conditions. The Company evaluates its estimates on an ongoing basis. Changes in estimates are reflected in reported results in the period in which they become known by the Company’s management. Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents are short-term, highly liquid investments with original maturities of three months or less at the date of purchase. Investments qualifying as cash equivalents primarily consist of money market funds, commercial paper, corporate notes and bonds and certificates of deposit. Cash accounts with any type of restriction are classified as restricted cash. If restrictions are expected to be lifted in the next twelve months, the restricted cash account is classified as current. As of December 31, 2016 and 2015, the Company recorded restricted cash of $0.8 million and $0.7 million, respectively, which was primarily related to the Company’s facility lease. Marketable Securities The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available-for-sale. Available-for-sale securities may consist of U.S. government agencies securities, commercial paper, corporate notes and bonds and certificates of deposit, which are maintained by an investment manager. Available-for-sale securities are carried at fair value, with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ deficit until realized. To determine whether an other-than-temporary impairment exists, the Company performs an analysis to assess whether it intends to sell, or whether it would more likely than not be required to sell, the security before the expected recovery of the amortized cost basis. Where the Company intends to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary and the full amount of the unrealized loss is recognized on the statement of operations and comprehensive loss as an other-than-temporary impairment charge. When this is not the case, the Company performs additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where the Company does not expect to receive cash flows, based on using a single best estimate, sufficient to recover the amortized cost basis of a security and amount of the loss recognized in other income (expense). Realized gains and losses are recognized in interest income. Any premium or discount arising at purchase is amortized and/or accreted to interest income. Inventory The Company values its inventories at the lower of cost or net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials and manufacturing overhead, on a first-in, first-out basis. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded as a component of “Cost of revenues.” The Company capitalizes inventory costs associated with the Company’s products after regulatory approval when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized. Inventory acquired prior to receipt of marketing approval of a product candidate is expensed as research and development expense as incurred. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign. Shipping and handling costs for product shipments are recorded as incurred as a component of “Cost of revenues” along with amortization expense related to definite-lived intangible assets, costs associated with manufacturing the product and any inventory reserves or write-downs. 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. The Company commences amortization of indefinite-lived intangible assets, such as IPR&D, once the associated research and development efforts have been completed. The Company amortizes these product-related intangible assets over their estimated useful lives, and amortization expense is recorded as a component of “Cost of revenues.” The Company amortizes other definite-lived assets, such as core technology, over their estimated useful lives as a component of “Research and development expenses.” Definite-lived intangible assets are evaluated for impairment whenever events or circumstances indicate that the carrying value may not be fully recoverable. 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. Revenue Recognition The Company recognizes revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; delivery has occurred or services have been rendered; the price to the customer is fixed or determinable; and collectability is reasonably assured. Product Revenues, Net The Company sells ONIVYDE to a limited number of specialty pharmaceutical distributors in the United States (collectively, its “Distributors”). The Company’s Distributors subsequently resell the products to healthcare providers. The Company recognizes revenue on product sales when title and risk of loss have passed to the Distributor, which is typically upon delivery. Product revenues are recorded net of applicable reserves for discounts and allowances. As a result of the Asset Sale, all product revenue relates to the Commercial Business and has 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 estimates its net product revenues by deducting from its gross product revenues trade allowances, estimated contractual discounts, estimated Medicaid rebates, estimated reserves for product returns and estimated costs of other incentives offered to patients. These discounts and allowances are based on estimates of the amounts earned or to be claimed on the related sales. The Company’s estimates take into consideration its historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted Distributor buying and payment patterns. Actual amounts may ultimately differ from the Company’s estimates. If actual results vary, the Company will adjust these estimates, which could have an effect on earnings in the period of adjustment. Product revenue reserves and allowances that reduce gross revenue are categorized as follows: Trade Allowances: The Company pays fees to its Distributors for providing certain data to the Company as well as for maintaining contractual inventory and service levels. These trade allowances are recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized. Rebates and Chargeback Discounts: The Company is subject to discount obligations under state Medicaid programs and the Public Health Service 340B Drug Pricing Program, contracts with Federal government entities purchasing via the Federal Supply Schedule and various private organizations, such as group purchasing organizations (collectively, its “Third-party Payors”). The Company estimates the rebates and chargeback discounts it will provide to Third-party Payors, based upon its estimated payor mix, and deducts these estimated amounts from its gross product revenues at the time revenue is recognized. Chargeback discounts are processed when the Third-party Payor purchases the product at a discount from the Distributor, who then in turn charges back to the Company the difference between the price initially paid by the Distributor and the discounted price paid by the Third-party Payor. These chargeback discounts are recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized. Rebates that are invoiced directly to the Company are recorded as accrued liabilities on the consolidated balance sheet at the time revenue is recognized. Product Returns: An allowance for product returns is established for returns expected to be made by Distributors and is recorded at the time revenue is recognized, resulting in a reduction to product sales. In accordance with contractual terms, Distributors have the right to return unopened and undamaged product that is within a permissible number of months before and after the product’s expiration date, subject to contractual limitations. The Company has the ability to monitor inventory levels and the shelf life of product at Distributors and can contractually control the amount of inventory that is sold to Distributors. Based on inventory levels held by Distributors and the structure of the Company’s distribution model, the Company has concluded that it has the ability to reasonably estimate product returns at the time revenue is recognized. The Company’s estimated rate of return is based on historical rates of return for comparable oncology products. Other Incentives: The Company offers co-pay mitigation support to commercially insured patients. The Company’s co-pay mitigation program is intended to reduce each participating patient’s portion of the financial responsibility for a product’s purchase price to a specified dollar amount. Based upon the terms of the Company’s co-pay mitigation program, the Company estimates average co-pay mitigation amounts in order to establish a reserve for co-pay mitigation claims and deducts these estimated amounts from its gross product revenues at the later of the date that (i) the revenues are recognized or (ii) the incentive is offered. Claims under the Company’s co-pay mitigation program are subject to expiration. All product revenue recognized relates to the Commercial Business and is presented as income (loss) from discontinued operations, net of tax in the condensed consolidated statements of operations for all periods presented. All balance sheet accounts described above are included in the assets or liabilities for discontinued operation for all periods presented. License and Collaboration Revenues The Company enters into biopharmaceutical product development agreements with collaborative partners for the research and development of therapeutic and diagnostic products. The terms of the agreements may include nonrefundable signing and licensing fees, funding for research, development and manufacturing, milestone payments and royalties or profit-sharing on any product sales derived from collaborations. These multiple-element arrangements are analyzed to determine whether the deliverables can be separated or whether they must be accounted for as a single unit of accounting. The revenue recognition guidance related to multiple-element arrangements requires entities to separate and allocate consideration in a multiple-element arrangement according to the relative selling price of each deliverable. The fair value of deliverables under the arrangement may be derived using a best estimate of selling price if vendor specific objective evidence and third-party evidence are not available. Deliverables under the arrangement will be separate units of accounting provided that a delivered item has value to the customer on a stand-alone basis and if the arrangement does not include a general right of return relative to the delivered item and delivery or performance of the undelivered item is considered probable and substantially in the control of the vendor. In September 2014, the Company entered into a license and collaboration agreement (the “Baxalta Agreement”) with Baxter International Inc., Baxter Healthcare Corporation and Baxter Healthcare SA (collectively, “Baxter”) for the development and commercialization of ONIVYDE outside of the United States and Taiwan (the “Licensed Territory”). In connection with Baxter International Inc.’s separation of the Baxalta business, the Baxalta Agreement was assigned to Baxalta Incorporated, Baxalta US Inc. and Baxalta GmbH (collectively, “Baxalta”) during the second quarter of 2015. The Baxalta Agreement was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements. The Company determined that the obligations under this agreement represent a single unit of accounting and that the agreement represents a services agreement. As a result, the Company has estimated the level of effort expected to be completed as a result of providing the identified deliverables and will recognize revenue related to the agreement based on proportional performance as effort is completed over the expected services period. The Company also entered into a collaboration agreement with Watson Laboratories, Inc. (“Actavis”) in November 2013, which was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements. All operating results recognized related to the Baxalta Agreement and Actavis Agreement are presented as income (loss) from discontinued operations, net of tax in the condensed consolidated statements of operations for all periods presented. In addition, in the condensed consolidated balance sheet as of December 31, 2016, 2015 and 2014, the assets and liabilities related to the Baxalta Agreement and Actavis Agreement have been presented separately. 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. Milestone

Discontinued Operations - Sale

Discontinued Operations - Sale of Commercial Business	12 Months Ended
	Dec. 31, 2016
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 a loss from discontinued operations, net of tax in the condensed consolidated statements of operations for all periods presented. In addition, in the condensed consolidated balance sheet as of December 31, 2016, 2015 and 2014, 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, 2016, 2015 and 2014 reflect the operations of the Commercial Business as a discontinued operation. Discontinued operations for the years ended December 31, 2016, 2015 and 2014 includes the following: (in thousands) Years Ended December 31, 2016 2015 2014 Revenues: Product revenues, net $ 53,064 $ 4,328 $ — License and collaboration revenues 87,119 84,930 10,460 Other revenues 4,090 — — Total revenues 144,273 89,258 10,460 Costs and expenses: Cost of revenues 6,912 46 — Research and development expenses 51,352 39,955 35,185 Selling, general and administrative expenses 48,677 33,747 11,751 Restructuring expenses 146 — — Total costs and expenses 107,087 73,748 46,936 Other income and expenses: Interest expense (21,196 ) (463 ) — Income (loss) from discontinued operations $ 15,990 $ 15,047 $ (36,476 ) Income tax expense (13,224 ) (11,215 ) — Total income (loss) from discontinued operations $ 2,766 $ 3,832 $ (36,476 ) The carrying value of the assets and liabilities of the Commercial Business classified as “Assets held for sale” in the condensed consolidated balance sheets are as follows: (in thousands) December 31, 2016 December 31, 2015 Assets Current assets: Accounts receivable, net $ 17,194 $ 6,472 Inventory 14,554 3,717 Prepaid expenses and other current assets 1,547 1,273 Total current assets held for sale 33,295 11,462 Property and equipment, net 1,553 1,814 Intangible assets, net 3,977 4,555 Goodwill 3,605 3,605 Total long-term assets held for sale 9,135 9,974 Liabilities Current liabilities: Accounts payable, accrued expenses and other 21,312 15,343 Deferred revenues 36,226 50,137 Total current liabilities held for sale 57,538 65,480 Deferred revenues, net of current portion 25,673 51,197 Total long-term liabilities held for sale 25,673 51,197 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.

Consolidated Subsidiaries

Consolidated Subsidiaries	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Consolidated Subsidiaries	3. Consolidated Subsidiaries Silver Creek Pharmaceuticals, Inc. On August 20, 2010, the Company acquired a controlling interest in Silver Creek. The Company has concluded that Silver Creek is a variable interest entity and that the Company is the primary beneficiary. The Company has the ability to direct the activities of Silver Creek through its ownership percentage and through the board of director seats controlled by the Company and its de facto agents. As such, Silver Creek is consolidated by the Company. During the year ended December 31, 2014, Silver Creek issued convertible notes to various lenders in the aggregate principal amount of $1.0 million. As of December 31, 2014, these outstanding borrowings and related accrued interest converted into shares of Silver Creek Series A preferred stock at the Series A preferred stock value of $1.00 per share. As a result of changes to the ownership composition of Silver Creek as of December 31, 2014, the non-controlling interest in Silver Creek increased by approximately $0.4 million. During the year ended December 31, 2015, Silver Creek issued and sold a total of 1.6 million shares of Silver Creek Series B preferred stock at a price of $1.35 per share to investors and received net cash proceeds of $2.1 million, after deducting issuance costs. As a result of changes to the ownership composition of Silver Creek as of December 31, 2015, the non-controlling interest in Silver Creek increased by approximately $0.9 million. As described more fully in Note 11, “Borrowings,” Silver Creek issued $1.0 million of convertible promissory notes (the “Silver Creek Notes”) in May 2016. In August 2016, Silver Creek issued $0.2 million of additional Silver Creek Notes under the same terms as the May 2016 issuance. In December 2016, these outstanding borrowings and related accrued interest were converted into shares of Silver Creek Series C preferred stock at the Series C preferred stock value of $1.50 per share. In addition, Silver Creek sold 1.5 million additional shares of its Series C preferred stock to new investors at a price of $1.50 per share and received net cash proceeds of $2.1 million, after deducting issuance costs. In conjunction with this sale, Silver Creek also issued warrants to purchase 1.9 million shares of Silver Creek Series C preferred stock to the same new investors. As a result of changes to the ownership composition of Silver Creek as of December 31, 2016, the non-controlling interest in Silver Creek decreased by approximately $0.8 million. As of December 31, 2016 and 2015, the Company owned approximately 50% and 56% of the outstanding voting stock of Silver Creek, respectively, and recorded a non-controlling interest of approximately $(1.5) million and $0.2 million, respectively, as a component of mezzanine equity on the Company’s consolidated balance sheets based on the terms of the Silver Creek Series A, Series B and Series C preferred stock. As of December 31, 2016, the Company consolidated Silver Creek’s total assets and total liabilities of $2.0 million and $2.0 million, respectively. As of December 31, 2015, the Company consolidated Silver Creek’s total assets and total liabilities of $0.8 million and $0.2 million, respectively. As of December 31, 2016 and 2015, the Company’s unrestricted cash and cash equivalents balance included $1.9 million and $0.7 million, respectively, of cash and cash equivalents held by Silver Creek that is designated for the operations of Silver Creek. Merrimack Pharmaceuticals (Bermuda) Ltd. Merrimack Pharmaceuticals (Bermuda) Ltd. was incorporated in Bermuda during 2011 and merged with and into the Company during the third quarter of 2014.

Net Loss Per Common Share

Net Loss Per Common Share	12 Months Ended
	Dec. 31, 2016
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 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, 2016, 2015 and 2014, as the Company was in a loss position and had no shares that met the definition of participating securities outstanding as of December 31, 2016, 2015 and 2014. 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 remain outstanding. The stock options, warrants and conversion premium on the Convertible Notes are excluded from the calculation of diluted loss per share because the net loss for the years ended December 31, 2016, 2015 and 2014 causes such securities to be anti-dilutive. Securities excluded from the calculation of diluted loss per share are shown in the chart below: Years Ended December 31, (in thousands) 2016 2015 2014 Common stock warrants — — 238 Outstanding options to purchase common stock 1,903 1,921 1,957 Conversion of the Convertible Notes 1,216 2,500 2,500

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2016
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 sale of the Commercial Business, 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. Sanofi On September 30, 2009, the Company and Sanofi entered into a license and collaboration agreement (the “Sanofi Agreement”) for the development and commercialization of MM-121. The Sanofi Agreement became effective on November 10, 2009, and Sanofi paid the Company a nonrefundable, noncreditable upfront license fee of $60.0 million. On June 17, 2014, the Company and Sanofi agreed to terminate the Sanofi Agreement effective December 17, 2014. In connection with the agreement to terminate the Sanofi Agreement, among other things, Sanofi transferred ownership of the investigational new drug application for MM-121 back to the Company in July 2014, and the Company waived Sanofi’s obligation to reimburse the Company for MM-121 development costs incurred after the effective termination date. Following the termination of the Sanofi Agreement, the Company is not entitled to receive any additional fees, milestone payments or reimbursements from the collaboration. The Company received total milestone payments of $25.0 million pursuant to the Sanofi Agreement. Under the Sanofi Agreement, Sanofi was responsible for all MM-121 development and manufacturing costs. Sanofi reimbursed the Company for direct costs incurred in both development and manufacturing and compensated the Company for its internal development efforts based on a full time equivalent rate. The Company recognized cost reimbursements for MM-121 development services within the period they were incurred and billable. Billable expenses were identified during each specified budget period. In the event that total development services expense incurred and expected to be incurred during the same period exceeded the total contractually allowed billable amount for development services during that period, the Company recognized only a percentage of the development services incurred as revenue during that period. At the inception of the collaboration, the Company determined that the license, the right to future technology, back-up compounds, participation on steering committees and manufacturing services performance obligations comprising the Sanofi Agreement represented a single unit of accounting. As the Company could not reasonably estimate its level of effort over the collaboration, the Company recognized revenue from the upfront payment, milestone payments and manufacturing services payments using the contingency-adjusted performance model over the expected development period, which was initially estimated at 12 years from the effective date of the Sanofi Agreement. As a result of the Company and Sanofi agreeing to terminate the Sanofi Agreement, the development period was revised to end as of December 17, 2014. Accordingly, the balance of the deferred revenue remaining on April 1, 2014 was recognized prospectively on a straight-line basis over the remaining development period, ending on December 17, 2014, in accordance with current generally accepted principles on revenue recognition. The Company recognized no revenue under the Sanofi agreement during the years ended December 31, 2016 or 2015. During the year ended December 31, 2014, the Company recognized revenue based on the following components of the Sanofi agreement: (in thousands) Year Ended December 31, 2014 Upfront payment $ 39,306 Milestone payment 16,377 Development services 18,904 Manufacturing services and other 17,709 Total $ 92,296 The Company performed development services for which revenue was recognized under the Sanofi Agreement in accordance with the specified budget period. During the year and specified budget periods ended December 31, 2013, the Company performed $10.1 million of development services in excess of recognized revenue. Of this amount, approximately $5.8 million was recognized as increased revenue in the year ended December 31, 2014 related to expenses incurred prior to December 31, 2013 upon the Company receiving budget approval for these overruns. The Company maintained no assets or liabilities related to the Sanofi Agreement as of either December 31, 2016 or 2015.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	6. Fair Value of Financial Instruments Fair value is an exit price, representing the amount that would be received from the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value is determined based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect certain market assumptions. As a basis for considering such assumptions, GAAP establishes a three-tier value hierarchy, which prioritizes the inputs used to develop the assumptions and for measuring fair value as follows: (Level 1) observable inputs such as quoted prices in active markets for identical assets; (Level 2) inputs other than the quoted prices in active markets that are observable either directly or indirectly; and (Level 3) unobservable inputs in which there is little or no market data, which requires the Company to develop its own assumptions. This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value. Recurring Fair Value Measurements The carrying values of cash, restricted cash, prepaid expenses, accounts receivable, accounts payable and accrued expenses, and other short-term assets and liabilities approximate their respective fair values due to the short-term maturities of these assets and liabilities. The following tables summarize assets and liabilities measured at fair value on a recurring basis as of December 31, 2016 and 2015 and the input categories associated with those assets and liabilities: December 31, 2016 (in thousands) Level 1 Level 2 Level 3 Assets: Money market funds $ 12,373 $ — $ — Totals $ 12,373 $ — $ — Liabilities: Silver Creek warrant liability $ — $ — $ 1,499 Totals $ — $ — $ 1,499 December 31, 2015 (in thousands) Level 1 Level 2 Level 3 Assets: Money market funds $ 704 $ — $ — Totals $ 704 $ — $ — In December 2016, Silver Creek issued warrants to purchase an aggregate of 1.9 million shares of Silver Creek Series C preferred stock (the “Silver Creek warrants”). The issuance of the Silver Creek warrants is described more fully in Note 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. Changes in the fair value of the Silver Creek warrants in subsequent periods will be recognized as a component of “Other income, net” in the consolidated statements of operations and comprehensive loss. There were no changes in valuation techniques or transfers between the fair value measurement levels during the years ended December 31, 2016 or 2015. There were no liabilities measured at fair value on a recurring basis as of December 31, 2015. Non-Recurring Fair Value Measurements Certain assets, including IPR&D intangible assets, may be measured at fair value on a non-recurring basis in periods subsequent to initial recognition. As described more fully in Note 8, “Intangible Assets, Net,” the Company performed an interim impairment assessment during the fourth quarter of 2016 on the Company’s IPR&D asset related to the antibody-targeted nanotherapeutic that contains a chemotherapy drug. The Company utilized a probability-weighted discounted cash flow analysis under the income approach in performing this assessment. As a result of this interim impairment assessment, the fair value of this IPR&D asset was determined to be zero as of December 31, 2016. No non-recurring fair value measurements were required during the year ended December 31, 2015. Other Fair Value Measurements The estimated fair value of the Convertible Notes was $57.5 million as of December 31, 2016. The Company estimated the fair value of the Convertible Notes by using a quoted market rate in an inactive market, which is classified as a Level 2 input. The carrying value of the Convertible Notes was $47.0 million as of December 31, 2016 due to the bifurcation of the conversion feature of the Convertible Notes as described more fully in Note 11, “Borrowings.” 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.

Marketable Securities

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

Intangible Assets, Net

Intangible Assets, Net	12 Months Ended
	Dec. 31, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Assets, Net	8. Intangible Assets, Net As part of the acquisition of Hermes BioSciences, Inc. (“Hermes”) on October 6, 2009, the Company acquired IPR&D assets of $2.8 million related to MM-302, an antibody-targeted nanotherapeutic program that contains a chemotherapy drug. In December 2016, the Company determined that it would be stopping the ongoing Phase 2 clinical trial of MM-302, which utilized the antibody-targeted nanotheraputic that contains a chemotherapy drug. The decision to stop the trial was made following an independent Data and Safety Monitoring Board (the “DSMB”) opinion that continuing the clinical trial would be unlikely to demonstrate benefit over the comparator treatments. Subsequent to this recommendation, a futility assessment was performed that confirmed the DSMB’s opinion. Both the treatment and control arms were found to have shorter than expected median progression free survival. While patients currently enrolled in the clinical trial may choose to continue on their assigned treatment based upon discussion with their study physician, no further development of MM-302 is being contemplated by the Company at this time. As a result of this determination, the Company recorded an impairment charge of $2.8 million during the fourth quarter of 2016. This impairment charge was recorded as a component of “Research and development expenses” within the consolidated statements of operations and comprehensive loss. The Company did not have any intangible assets as of December 31, 2016, and the intangible assets as of December 31, 2015 consisted of the following: December 31, 2015 (in thousands) Gross C Accumulated Amortization Net Carrying Value IPR&D 2,800 — 2,800

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Property and Equipment, Net	9. Property and Equipment, Net Property and equipment, net as of December 31, 2016 and 2015 consisted of the following: December 31, (in thousands) 2016 2015 Lab equipment $ 17,537 $ 16,325 IT equipment 8,509 7,733 Leasehold improvements 20,633 20,507 Furniture and fixtures 626 635 Construction in process 378 2,243 Total property and equipment, gross 47,683 47,443 Less: Accumulated depreciation (33,471 ) (27,342 ) Total property and equipment, net $ 14,212 $ 20,101 Depreciation expense was $6.5 million, $4.8 million and $3.7 million for the years ended December 31, 2016, 2015 and 2014, respectively. Capitalized interest costs were insignificant for the years ended December 31, 2016, 2015 and 2014. During the year ended December 31, 2016, the Company recognized a $0.5 million charge related to the disposal of property and equipment. There were no significant losses recognized related to the disposal of property and equipment during the years ended December 31, 2015 or 2014.

Accounts Payable, Accrued Expen

Accounts Payable, Accrued Expenses and Other	12 Months Ended
	Dec. 31, 2016
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, 2016 and 2015 consisted of the following: December 31, (in thousands) 2016 2015 Accounts payable $ 2,692 $ 3,848 Accrued goods and services 7,534 8,283 Accrued clinical trial costs 8,776 9,170 Accrued drug purchase costs 480 6,620 Accrued payroll and related benefits 3,394 5,313 Accrued restructuring expenses 774 — Accrued interest 2,100 3,041 Accrued dividends payable 19 19 Silver Creek warrant liability 1,499 — Deferred tax incentives 1,402 445 Total accounts payable, accrued expenses and other $ 28,670 $ 36,739

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Borrowings	11. Borrowings 2022 Notes On December 22, 2015, the Company closed a private placement of $175.0 million aggregate principal amount of 11.50% 2022 Notes and entered into an indenture (the “U.S. Bank Indenture”) with U.S. Bank National Association as trustee and collateral agent (the “2020 Notes Trustee”). As a result of this placement, the Company received net proceeds of approximately $168.5 million, after deducting private placement and offering expenses payable by the Company. The private placement and offering expenses included $0.9 million of transaction costs that were expensed in accordance with the debt modification guidance per ASC 470, Debt The Company may redeem the 2022 Notes at its option, in whole or in part from time to time at a price equal to the principal amount plus accrued interest and a specified make-whole premium. If the Company experiences certain change of control events as defined in the U.S. Bank Indenture, the holders of the 2022 Notes will have the right to require the Company to purchase all or a portion of the 2022 Notes at a purchase price in cash equal to 101% of the principal amount thereof, plus accrued and unpaid interest to the date of purchase. In addition, upon certain Asset Sale events as defined in the U.S. Bank Indenture, the Company may be required to offer to use the net proceeds thereof to purchase all or a portion of the 2022 Notes at 100% of the principal amount thereof, plus accrued and unpaid interest to the date of purchase. The 2022 Notes are senior secured obligations of the Company and will be equal in right of payment to all existing and future pari passu indebtedness of the Company (including the Company’s outstanding Convertible Notes), will be senior in right of payment to all existing and future subordinated indebtedness of the Company, will have the benefit of a security interest in the 2022 Notes collateral and will be junior in lien priority in respect of any asset-based lending collateral that secures any first priority lien obligations from time to time. The 2022 Notes contain customary covenants, including covenants that limit or restrict the Company’s ability to incur liens, incur indebtedness, and make certain restricted payments, but do not contain covenants related to future financial performance. The 2022 Notes are secured by a first priority lien on substantially all of the Company’s assets. The 2022 Notes contain customary events of default. Upon certain events of default occurring, the 2022 Notes Trustee may declare 100% of the principal of and accrued and unpaid interest, if any, on all the 2022 Notes to be due and payable. In the case of certain events of bankruptcy, insolvency or reorganization involving the Company or a restricted subsidiary, 100% of the principal of, and accrued and unpaid interest on, the 2022 Notes will automatically become due and payable. There have been no events of default as of or during the year ended December 31, 2016. The Company assessed the 2022 Notes pursuant to ASC 815, Derivatives and Hedging Debt issuance costs incurred by the Company, excluding costs allocated to the debt modification as discussed below, are accounted for as a direct deduction to the carrying value of the 2022 Notes and are amortized to interest expense using the effective interest method over the life of the 2022 Notes. The effective interest rate associated with the 2022 Notes is 12.32%. For the years ended December 31, 2016 and 2015, interest expense related to the 2022 Notes was approximately $20.9 million and $0.5 million, respectively, income (loss) from discontinued operations, net of tax on the consolidated statement of loss and comprehensive loss. In connection with the completion of the Asset Sale on April 3, 2017, the liability under the 2022 Notes was satisfied. Convertible Notes In July 2013, the Company issued $125.0 million aggregate principal amount of Convertible Notes in an underwritten public offering. The Company issued the Convertible Notes under an indenture, dated as of July 17, 2013 (the “Base Indenture”) between the Company and Wells Fargo Bank, National Association, as trustee (the “Convertible Notes Trustee”), as supplemented by a supplemental indenture, dated as of July 17, 2013, between the Company and the Convertible Notes Trustee (together with the Base Indenture, the “Wells Fargo Indenture”). As a result of the Convertible Notes offering, the Company received net proceeds of approximately $120.6 million, after deducting underwriting discounts and commissions and offering expenses payable by the Company. The Convertible Notes bear interest at a rate of 4.50% per year, payable semiannually in arrears on January 15 and July 15 of each year, beginning on January 15, 2014. The Convertible Notes are general unsecured senior obligations of the Company and rank (i) pari passu in seniority with respect to the 2022 Notes, (ii) senior in right of payment to any of the Company’s indebtedness that is expressly subordinated in right of payment to the Convertible Notes, (iii) equal in right of payment to any of the Company’s unsecured indebtedness that is not so subordinated, (iv) effectively junior in right of payment to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness and (v) structurally junior to all indebtedness and other liabilities (including trade payables) of the Company’s subsidiaries. The Company separately accounted for the liability and equity components of the Convertible Notes by bifurcating gross proceeds between the indebtedness, or liability component, and the embedded conversion option, or equity component. This bifurcation was done by estimating an effective interest rate as of the date of issuance for similar notes which do not contain an embedded conversion option. The gross proceeds received from the issuance of the Convertible Notes less the initial amount allocated to the indebtedness resulted in a $53.8 million allocation to the embedded conversion option. The embedded conversion option was recorded in stockholders’ deficit and as debt discount, to be subsequently amortized as interest expense over the term of the Convertible Notes. Underwriting discounts and commissions and offering expenses totaled $4.4 million and were allocated to the indebtedness and the embedded conversion option based on their relative values. On April 13, 2016, the Company entered into separate, privately-negotiated conversion agreements (the “Conversion Agreements”) with certain holders of the Convertible Notes. Under the Conversion Agreements, such holders agreed to convert an aggregate principal amount of $64.2 million of Convertible Notes held by them. The Company initially settled each $1,000 principal amount of Convertible Notes surrendered for conversion by delivering 136 shares of the Company’s common stock on April 18, 2016. In total, the Company issued an aggregate of 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 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 have been no events of default as of or during the year ended December 31, 2016. For the years ended December 31, 2016, 2015 and 2014, interest expense related to the Convertible Notes was $22.7 million, $13.7 million and $13.7 million, respectively. As discussed above, interest expense for the year ended December 31, 2016 includes the loss on extinguishment of $14.6 million associated with the April 2016 conversion of the Convertible Notes as well as $0.2 million of related transaction costs. Loan Agreement In November 2012, the Company entered into the Loan Agreement with Hercules pursuant to which the Company received loans in the aggregate principal amount of $40.0 million. The Company, as permitted under the Loan Agreement, had previously extended the interest-only payment period with the aggregate principal balance of the loans to be repaid in monthly installments starting on June 1, 2014 and continuing through November 1, 2016. On June 25, 2014, the Company entered into an amendment to the Loan Agreement, whereby the Company and Hercules agreed to extend until October 1, 2014 the period during which the Company makes interest-only payments. On November 6, 2014, the Company entered into a further amendment to the Loan Agreement, whereby the Company and Hercules agreed to extend by four additional months the period during which the Company makes interest-only payments. On February 25, 2015, the Company entered into a fourth amendment to the Loan Agreement pursuant to which the Company and Hercules agreed to extend the maturity date and the period during which the Company makes interest-only payments on its current loans in the aggregate principal amount of $40.0 million. As a result of this amendment, the Company was required to repay the outstanding aggregate principal balance of the loan beginning on June 1, 2016 and continuing through November 1, 2018. As a result of the FDA’s approval of the Company’s NDA for ONIVYDE, which occurred on October 22, 2015, the Company elected to extend the interest-only period by an additional six months such that the Company would repay the outstanding aggregate principal balance of the loans beginning on December 1, 2016 and continuing through November 1, 2018. This amendment was treated as a debt modification for accounting purposes. Upon the earlier of full repayment of the loans or November 1, 2016, the Company was required to pay Hercules a fee of $1.2 million, which had been recorded as a discount to the loans and as a long-term liability on the Company’s consolidated balance sheets. Additionally, the Company reimbursed Hercules for costs incurred related to the loans, which was reflected as a discount to the carrying value of the loans. The Company amortized these loan discounts totaling $1.6 million to interest expense over the term of the loans using the effective interest method. In connection with the Loan Agreement, the Company granted Hercules a security interest in all of the Company’s personal property now owned or hereafter acquired, excluding intellectual property but including the proceeds from the sale, if any, of intellectual property, and a negative pledge on intellectual property. The Loan Agreement also contained certain representations, warranties and non-financial covenants of the Company. During the fourth quarter of 2015, the Company repaid the loans in full in conjunction with the issuance of the 2022 Notes. The total repayment amount included the $40.0 million in outstanding principal, the $1.2 million fee discussed above and interest accrued up through the repayment date. The Company assessed the repayment of the Loan Agreement with Hercules in conjunction with the issuance of the 2022 Notes, of which Hercules holds a portion, in accordance with the debt extinguishment and modification guidance per ASC 470, Debt For the years ended December 31, 2015 and 2014, interest expense related to the Hercules loans was $5.4 million and $4.7 million, respectively. No interest expense related to the Hercules loans was recognized during the year ended December 31, 2016. Credit Facility On November 8, 2016, the Company entered into a Loan and Security Agreement (the “Credit Agreement”) with BioPharma Credit Investments IV Sub, LP (“Pharmakon”) pursuant to which a credit facility of an aggregate principal amount of at least $15.0 million and up to $25.0 million is available. If the Company borrows under the Credit Agreement, the credit facility will bear 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 majority owned subsidiary, Silver Creek, entered into a Note Purchase Agreement pursuant to which it issued convertible notes to various lenders in aggregate principal amounts of $1.6 million in December 2012, $0.9 million during the year ended December 31, 2013 and $1.0 million during the year ended December 31, 2014. The notes issued pursuant to the Note Purchase Agreement bore interest at 6% per annum. Upon issuance, these convertible notes contained a feature wherein if at any time prior to maturity Silver Creek enters into a qualifying equity financing, defined as a sale or series of related sales of equity securities prior to the maturity date and resulting in at least $4.0 million of gross proceeds, the notes would automatically convert into the next qualifying equity financing at a 25% discount. The Company determined that this convertible feature met the definition of a derivative and required separate accounting treatment. The derivative was estimated to be valued at $0.2 million using a probability-weighted model and was recorded as derivative liability on the consolidated balance sheets. For the year ended December 31, 2014, the derivative was remeasured upon conversion of the notes with the gain in remeasurement recognized in other income. The specific notes that were outstanding as of December 31, 2014 matured and converted, along with an immaterial amount of accrued interest into shares of Silver Creek Series A preferred stock on December 31, 2014. In May 2016, Silver Creek issued an aggregate of $1.0 million of Silver Creek Notes. In August 2016, Silver Creek issued $0.2 million of additional Silver Creek Notes under the same terms as the May 2016 issuance. The Silver Creek Notes were automatically convertible into shares of Silver Creek equity under a variety of conversion scenarios. The Silver Creek Notes bore interest at 6% per annum and were set to mature and convert, along with accrued interest, into Silver Creek Series B preferred stock at a conversion price of $1.35 per share on December 31, 2016. If, prior to maturity, Silver Creek entered into a sale or series of related sales of equity securities resulting in at least $4.0 million of gross proceeds, the Silver Creek Notes would convert into the equity securities sold at the lesser of the price paid per share for the equity securities or $1.60 per share. Principal and accrued interest related to the Silver Creek Notes were not permitted to be paid in cash by Silver Creek without the consent of a majority of the noteholders. In December 2016, Silver Creek executed a Series C Preferred Stock and Warrant Purchase Agreement (the “Silver Creek Series C Agreement”) whereby it agreed to sell 1.5 million shares of Silver Creek Series C preferred stock to new investors at a purchase price of $1.50 per share. In connection with this financing, holders of the Silver Creek Notes agreed to convert all principal and accrued interest associated with the Silver Creek Notes into 0.8 million shares of Silver Creek Series C preferred stock at a conversion price of $1.50 per share. New purchasers of the Silver Creek Series C preferred stock also received warrants to purchase an aggregate of 1.9 million shares of Silver Creek Series C preferred stock at a future date. The exercise price of the warrants varies based upon the achievement of certain milestone events defined in the related warrant agreements. Milestone Event 1 is defined as the date that is seven business days following the acceptance by the FDA of Silver Creek’s filing of an Investigational New Drug application (“IND”), or 30 business days after the IND is filed without FDA rejection of the application. Milestone Event 2 is defined as the date that is seven business days following the date when Silver Creek completes a Phase 1 clinical trial provided, that if Silver Creek receives proceeds of less than $4.0 million pursuant to the sale of Series C preferred stock, Milestone Event 2 shall mean the date that is seven business days following the first dose in humans in a clinical trial. Of the warrants to purchase 1.9 million shares of Silver Creek Series C preferred stock that were issued, warrants to purchase 1.2 million shares of Silver Creek Series C preferred stock are exercisable at an exercise price of $1.75 per share if the warrant is exercised prior to the date that is 30 business days after the date that the holder receives notice from Silver Creek of the achievement of Milestone Event 1, or $2.25 per share if the warrant is exercised on or after the date that is 30 business days after the holder receives notice from Silver Creek of the achievement of Milestone Event 1. The remaining warrants to purchase 0.7 million shares of Silver Creek Series C preferred stock are exercisable at an exercise price of $2.25 per share if the warrant is exercised prior to the date that is 30 business days after the date that the holder receives notice from Silver Creek of the achievement of Milestone Event 2, or $2.75 per share if the warrant is exercised on or after the date that is 30 business days after Milestone Event 2. All warrants to purchase Silver Creek Series C preferred stock are exercisable until the earliest of (i) the consummation of a Silver Creek liquidation event, (ii) the consummation of an initial public offering of Silver Creek common stock, (iii) four months after the achievement of Milestone Event 2 or (iv) seven years from the date of issuance. The warrants to purchase Silver Creek Series C preferred stock were classified as a current liability in accordance with ASC 480, Distinguishing Liabilities from Equity Future Minimum Payments under Outstanding Borrowings Future minimum payments under outstanding borrowings as of December 31, 2016 are as follows: (in thousands) Convertible Notes 2017 $ 2,736 2018 2,736 2019 2,736 2020 63,527 2021 and thereafter — Total 71,735 Less interest (10,943 ) Less unamortized discount (13,842 ) Less current portion — Long-term debt $ 46,950

Restructuring Activities

Restructuring Activities	12 Months Ended
	Dec. 31, 2016
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 (“CEO”). Under this corporate restructuring, the Company recognized total restructuring expenses of $5.7 million during the year ended December 31, 2016 related to stock-based compensation expense for certain terminated employees, contractual termination benefits for employees with pre-existing severance arrangements and one-time employee termination benefits. These one-time employee termination benefits were comprised of severance, benefits and related costs, all of which resulted in cash expenditures during the third and fourth quarters of 2016. The following table summarizes the charges related to the restructuring activities as of December 31, 2016: (in thousands) Expenses Less: Payments Less: Non-Cash Expenses Accrued Restructuring Expenses at December 31, 2016 Severance, benefits and related costs due to workforce reduction $ 5,710 $ (3,565 ) $ (1,371 ) $ 774 Totals $ 5,710 $ (3,565 ) $ (1,371 ) $ 774

Common Stock Warrants

Common Stock Warrants	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Common Stock Warrants	13. Common Stock Warrants The following is a description of the common stock warrant activity of the Company: (in thousands, except per share amounts) Warrants for the Purchase of Common Weighted Average Exercise Price Balance at December 31, 2013 278 $ 30.50 Exercised (40 ) $ 33.80 Balance at December 31, 2014 238 $ 30.00 Exercised (235 ) $ 30.00 Cancelled (3 ) $ 30.00 Balance at December 31, 2015 — $ — During the year ended December 31, 2014, warrants to purchase approximately 7,500 shares of common stock were cashless exercised and 3,800 shares of common stock were issued. During the year ended December 31, 2015, warrants to purchase approximately 229,500 shares of common stock were cashless exercised and 169,500 shares of common stock were issued. As of December 31, 2015, all remaining unexercised warrants for the purchase of common stock had expired and were cancelled.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Common Stock	14. 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, 2016 and 2015, the Company had 20.0 million shares of $0.01 par value common stock authorized. There were approximately 13.0 million and 11.6 million shares of common stock issued and outstanding as of December 31, 2016 and 2015, respectively.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	15. 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, 2016, there were 0.5 million shares remaining available for grant under the 2011 Plan. 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 the 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, 2016, 2015 and 2014, the Company issued options to purchase 0.4 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 vest immediately. The fair value of stock options granted to employees during the years ended December 31, 2016, 2015 and 2014 was estimated at the date of grant using the following assumptions: Years Ended December 31, 2016 2015 2014 Risk-free interest rate 1.1 – 2.0% 1.5 – 1.8% 1.6 – 2.0% Expected dividend yield 0% 0% 0% Expected term 5.0 – 5.8 years 5.0 – 5.9 years 5.0 – 5.9 years Expected volatility 67 – 69% 66 – 67% 64 – 72% The Company uses the simplified method to calculate the expected term as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term of its stock options. Under this approach, the expected term is calculated to be the average of the ten-year contractual term of the option and the weighted-average vesting term of the option, taking into consideration multiple vesting tranches. The computation of expected volatility is based on the historical volatility of comparable companies from a representative peer group selected based on industry and market capitalization. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected life of the stock options. Management estimates expected forfeitures based on historical experience and recognizes compensation costs only for those equity awards expected to vest. The Company recognized stock-based compensation expense during the years ended December 31, 2016, 2015 and 2014 as follows: Years Ended December 31, (in thousands) 2016 2015 2014 Employee awards: Research and development expense $ 6,083 $ 7,711 $ 6,434 General and administrative expense 4,685 5,392 5,276 Restructuring expense 1,371 — — Stock-based compensation expense for employee awards 12,139 13,103 11,710 Stock-based compensation expense for non-employee awards 1 58 268 Total stock-based compensation expense $ 12,140 $ 13,161 $ 11,978 The following table summarizes stock option activity during the year ended December 31, 2016: (in thousands, except per share amounts) Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Outstanding at December 31, 2015 1,921 $ 57.20 6.24 $ 47,963 Granted 426 $ 55.70 Exercised (196 ) $ 32.90 Forfeited (249 ) $ 70.40 Outstanding at December 31, 2016 1,902 $ 57.70 5.97 $ 7,564 Vested and expected to vest at December 31, 2016 1,879 $ 57.60 5.93 $ 7,564 Exercisable at December 31, 2016 1,497 $ 54.90 5.24 $ 7,564 The weighted-average grant date fair value of stock options granted during the years ended December 31, 2016, 2015 and 2014 was $33.20, $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, 2016, 2015 and 2014 was $5.6 million, $30.9 million and $19.8 million, respectively. As of December 31, 2016, there was $12.7 million of total unrecognized stock-based compensation expense related to unvested employee stock options. The Company expects to recognize this expense over a weighted-average period of approximately 1.7 years.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	16. Income Taxes 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, 2016 and 2015, the Company recognized an income tax benefit of $13.2 million and $11.2 million, respectively, in continuing operations and income tax expense in discontinued operations of $13.2 million and $11.2 million, respectively. The Company did not record income taxes for the year ended December 31, 2014 because there is a pre-tax loss from both continuing operations and discontinued operations. A reconciliation of the Company’s effective tax rate to the statutory federal income tax rate is as follows: Years Ended December 31, 2016 2015 2014 Federal income tax at statutory federal rate 35.0 % 35.0 % 35.0 % State taxes 0.6 1.2 3.7 Permanent differences (6.3 ) (2.4 ) (6.5 ) Stock-based compensation (1.5 ) (1.0 ) (2.7 ) Tax credits 12.6 9.0 24.1 Change in deferred state tax rate (0.3 ) (1.9 ) — Other 3.7 (0.5 ) 1.8 Change in valuation allowance (36.0 ) (32.5 ) (55.4 ) Total 7.8 % 6.9 % — % During the year ended December 31, 2014, the Company recorded a deferred tax liability related to the embedded conversion option of the Convertible Notes though equity. This deferred tax liability is reflected in the deferred tax table below, but is appropriately excluded from the effective tax rate. Temporary differences that give rise to significant net deferred tax assets as of December 31, 2016 and 2015 are as follows: December 31, (in thousands) 2016 2015 Deferred tax assets Net operating losses $ 194,027 $ 182,992 Capitalized research and development expenses 15,854 21,444 Credit carryforwards 144,823 93,113 Depreciation 2,557 2,128 Deferred compensation 12,463 11,664 Accrued expenses 3,601 1,807 Deferred revenue 21,935 10,999 Other temporary differences 25,276 17,235 Total gross deferred tax assets 420,536 341,382 Valuation allowance (414,558 ) (326,577 ) Net deferred tax assets 5,978 14,805 Deferred tax liabilities Intangible assets (1,428 ) (2,667 ) Debt discount (4,550 ) (12,138 ) Net deferred taxes $ — $ — The Company has included temporary differences for continuing and discontinuing operations in the table above because Ipsen did not acquire any of the Company’s temporary differences. The temporary differences related to the Commercial Business will reverse upon the sale to Ipsen and will be recorded in the second quarter of 2017 when the sale occurred. The Company concluded that there are no significant uncertain tax positions requiring recognition in the consolidated financial statements. The Company’s evaluation was performed for the tax years ended December 31, 2013 through 2016, the tax years which remain subject to examination by major tax jurisdictions as of December 31, 2016. However, to the extent the Company utilizes net operating losses from years prior to 2012, the statute remains open to the extent of the net operating losses utilized. The Company’s policy is to recognize interest and penalties for uncertain tax positions as a component of income tax expense. The Company has not recognized any interest and penalties historically through December 31, 2016. At December 31, 2016, the Company had net operating loss carryforwards for federal and state income tax purposes of $542.7 million and $367.4 million, respectively. Included in the federal and state net operating loss carryforwards is approximately $39.2 million and $25.2 million, respectively, of deduction related to the exercise of stock options. This amount represents an excess tax benefit, which will be realized when it results in reduction of cash taxes in accordance with ASC 718, Compensation – Stock Compensation Utilization of the net operating loss and research and development credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”), due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of net operating loss and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax. The Company completed an evaluation of ownership changes through September 30, 2016 to assess whether utilization of the Company’s net operating loss or research and development credit carryforwards would be subject to an annual limitation under Section 382 of the Internal Revenue Code. The Company believes that it may be able to utilize all of its tax attributes as a result of the analysis. To the extent an ownership change occurs in the future, the net operating loss and credit carryforwards may be subject to limitation. The Company has not yet conducted a study of its domestic research and development credit carryforwards and orphan drug credits. This study may result in an increase or decrease to the Company’s credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. As a result, there would be no impact to the consolidated statements of operations and comprehensive loss or consolidated statements of cash flows if an adjustment were required. The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2016, 2015 and 2014 was as follows: (in thousands) Balance at Beginning of Period Additions Deductions Balance at End of Period December 31, 2014 $ 207,304 $ 50,185 $ — $ 257,489 December 31, 2015 257,489 69,088 — 326,577 December 31, 2016 326,577 87,981 — 414,558

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	17. Commitments and Contingencies Operating Leases The Company leases its office, laboratory and manufacturing space under non-cancelable operating leases. During August 2012, the Company entered into an Indenture of Lease (the “Amended Lease”), which amended and restated its facility lease. The Amended Lease will terminate on June 30, 2019, but the Company retains an option to renew the Amended Lease with respect to all of the leased space for an additional period of five years. In March 2013, September 2013, February 2015 and July 2015, the Company entered into further facility lease amendments for additional space that are co-terminus with the Amended Lease. In total, the Company leases approximately 167,000 square feet at its corporate headquarters in Cambridge, Massachusetts. As part of the Amended Lease and subsequent amendments, the landlord agreed to reimburse the Company for a portion of tenant improvements made to the facility. As of December 31, 2016, the Company had received $9.5 million of tenant improvement reimbursements. Tenant improvement reimbursements are recorded within deferred rent and are amortized over the term of the lease as reductions to rent expense. In May 2016, the Company entered into a sublease agreement (the “Sublease”) whereby a subtenant agreed to lease 8,143 square feet of office and lab space from the Company. The Sublease terminates on December 31, 2017, but may be extended through June 30, 2019 if mutually agreed upon by the Company and the subtenant. Rental income received from the subtenant has been classified by the Company as reduction of rent expense. Total future minimum rental payments to be received by the Company from the subtenant as of December 31, 2016 are $0.6 million. Total rent expense was $5.0 million, $4.3 million and $3.4 million for the years ended December 31, 2016, 2015 and 2014, respectively. Future minimum lease payments to be made by the Company under non-cancelable operating leases as of December 31, 2016 are as follows: Years ended December 31, (in 2017 $ 8,108 2018 8,102 2019 4,082 Total future minimum lease payments $ 20,292

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Related Party Transactions	18. Related Party Transactions Related parties of the Company held approximately 7% of the outstanding shares of Silver Creek Series A and Series B preferred stock as of both December 31, 2016 and 2015. No shares of Silver Creek Series C preferred stock issued during December 2016 were held by related parties of the Company as of December 31, 2016.

Retirement Plan

Retirement Plan	12 Months Ended
	Dec. 31, 2016
Postemployment Benefits [Abstract]
Retirement Plan	19. Retirement Plan On May 31, 2002, the Company established a 401(k) defined contribution savings plan (the “401(k) Plan”) for its employees who meet certain service period and age requirements. Contributions are permitted up to the maximum allowed under the Internal Revenue Code of each covered employee’s salary. The 401(k) Plan permits the Company to contribute at its discretion. For the years ended December 31, 2016, 2015 and 2014, the Company made contributions of $1.3 million, $1.1 million and $0.8 million, respectively, to the 401(k) Plan.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	20. Selected Quarterly Financial Data (Unaudited) The following table contains quarterly financial information for 2016 and 2015. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands, except per share data) 2016 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 ) 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 income (loss) per common share Net loss from continuing operations (3.23 ) (4.07 ) (2.06 ) (2.93 ) Net income (loss) 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 ) First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands, except per share data) 2015 Research and development expenses 26,435 26,479 29,944 38,175 General and administrative expenses 4,712 5,824 5,989 7,523 Net loss from continuing operations (35,553 ) (25,426 ) (40,040 ) (50,600 ) Income from discontinued operations, net of tax 1,121 2,525 (2,346 ) 2,532 Net loss (34,432 ) (22,901 ) (42,386 ) (48,068 ) Net loss attributable to Merrimack Pharmaceuticals, Inc. (34,759 ) (22,778 ) (42,594 ) (47,826 ) Basic and dilutive net income (loss) per common share Net loss from continuing operations (3.35 ) (2.30 ) (3.58 ) (4.38 ) Net income (loss) from discontinued operations, net of tax 0.10 0.23 (0.21 ) 0.22 Net loss per share (3.24 ) (2.07 ) (3.79 ) (4.16 )

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Events	21. Subsequent Events Asset Sale On January 7, 2017, the Company entered into the Asset Sale Agreement with Ipsen. Pursuant to the Asset Sale Agreement, Ipsen will acquire the Company’s right, title and interest in the non-cash assets, equipment, inventory, contracts and intellectual property primarily related to or used in the Commercial Business. Ipsen will not acquire the Company’s rights to $33.0 million in net milestone payments that may become payable pursuant to the Baxalta Agreement, among other excluded assets. Pursuant to the Asset Sale Agreement, Ipsen will pay the Company $575.0 million in cash (subject to a working capital adjustment as provided in the Asset Sale Agreement) and will assume certain related liabilities. Following the closing of the asset sale, the Company may be entitled to up to $450.0 million of additional payments based on achievement by or on behalf of Ipsen of certain milestone events related to FDA approval of ONIVYDE for certain indications. The consummation of the transaction is subject to customary closing conditions, including, among others: (i) the receipt of the approval of the Company’s stockholders; (ii) the expiration or termination of the required waiting periods under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, which waiting periods expired on February 22, 2017; (iii) the absence of a breach of the Company’s representations and warranties that would cause a material adverse effect on the Commercial Business; (iv) the absence of a business material adverse effect; and (v) the performance of certain covenants in all material respects. The Asset Sale Agreement contains certain termination rights for the Company and Ipsen. Upon termination of the Asset Sale Agreement under specified circumstances, the Company would be required to pay Ipsen a termination fee of $25.0 million, including if the Asset Sale Agreement is terminated in connection with the Company accepting a superior proposal or because the Company’s Board of Directors has changed its recommendation of the sale to its stockholders. The termination fee will also be payable if the Asset Sale Agreement is terminated because the Company’s stockholders did not vote to adopt the Asset Sale Agreement and, prior to such termination, a proposal to acquire at least 50% of the consolidated assets of the Company with respect to the Commercial Business or at least 50% of the Company’s voting securities has been publicly disclosed and the Company enters into a definitive agreement with respect to such proposal within 12 months after such termination, which is subsequently consummated. In addition, the Company would be required to reimburse Ipsen for up to $3.0 million of its out-of-pocket expenses incurred in connection with the transaction and the Asset Sale Agreement if the Asset Sale Agreement is terminated because the Company’s stockholders do not vote to approve it. In addition to the foregoing termination rights, and subject to certain limitations, the Company or Ipsen may terminate the Asset Sale Agreement if the asset sale is not consummated by June 30, 2017. Ipsen has also agreed to sublease 68,409 square feet of the Company’s manufacturing facility at the closing of the asset sale. In addition, at the closing of the asset sale, the Company and Ipsen will enter into an intellectual property license agreement pursuant to which Ipsen will grant the Company an exclusive license with respect to the portion of the transferred patents relating to certain liposomal technology and a non-exclusive license to the remainder of the transferred patents, in both cases for use outside of the field in which the Commercial Business will operate. In turn, the Company will grant Ipsen a non-exclusive license with respect to the remaining patents owned by the Company at the closing for use in the field in which the Commercial Business will operate. January 2017 Corporate Restructuring On January 9, 2017, the Company announced that it will further reduce headcount in connection with the asset sale and the completion of its strategic pipeline review. Upon the closing of the asset sale, the Company will focus its development efforts on its MM-121, MM-141 and MM-310 programs. After the headcount reduction, the Company expects to have approximately 80 employees. The Company’s Board of Directors committed to this course of action on January 6, 2017, subject to the closing of the asset sale, which is contingent upon the closing conditions described above. The reduction in personnel is expected to be complete upon the later of the closing of the asset sale and March 10, 2017. The Company estimates that, if the asset sale closes, it will incur approximately $7.5 million to $8.5 million of restructuring expenses related to one-time employee termination benefits. These one-time employee termination benefits are comprised of severance, benefits and related costs, all of which are expected to result in cash expenditures. The specific timing of the incurrence and payment of these restructuring expenses is dependent upon the timing of the closing of the asset sale. Hiring of Chief Executive Officer On January 16, 2017, the Company announced the hiring of Richard Peters, M.D., Ph.D., as the Company’s new CEO, effective as of February 6, 2017. Dr. Peters was also elected as a member of the Company’s Board of Directors. The Company and Dr. Peters entered into an employment agreement commencing on February 6, 2017 whereby Dr. Peters will receive an annual base salary of $700,000 and is eligible for an annual bonus of up to 65% of his base salary. Dr. Peters also received a one-time signing bonus of $900,000. Subject to the further approval of the Company’s Board of Directors, the Company will also grant Dr. Peters an option to purchase a number of shares of the Company’s common stock equal to the lesser of (i) such number of shares that has a target grant date fair value of $3.5 million and (ii) 2.0 million shares, with an exercise price per share equal to the fair market value of the Company’s common stock on the date of grant. The option will vest over four years at the rate of 25% on February 6, 2018 and the remainder in equal quarterly installments over the following three years. Extension of Credit Facility Availability On February 23, 2017, the Company entered into an amendment to the Credit Agreement with Pharmakon whereby the availability of the credit facility was extended through April 27, 2017. The Company had not borrowed any amounts under the Credit Agreement as of March 1, 2017. Events Subsequent to Filing of the 2017 Third Quarter Form 10-Q (Unaudited) Convertible Notes Tender Offer On October 13, 2017, the Company commenced a cash tender offer (the “Tender Offer”) to purchase any and all of its remaining $25.0 million aggregate principal amount of outstanding Convertible Notes. Upon the terms and subject to the conditions set forth in the Company’s Offer to Purchase, dated October 13, 2017, and the related Letter of Transmittal, the Company offered to pay, 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. On November 10, 2017, the Tender Offer expired, at which time the Company accepted for purchase the $24,975,000 aggregate principal amount of the Convertible Notes, representing approximately 99.78% of the outstanding Convertible Notes, that were validly tendered and not validly withdrawn pursuant to the Tender Offer. Following settlement of the Tender Offer, which occurred on November 14, 2017, $56,000 aggregate principal amount of the Convertible Notes remains outstanding.

Nature of the Business and Su28

Nature of the Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Segment Information	Segment Information Operating segments are defined as components of an enterprise engaging in business activities for which discrete financial information is available and regularly reviewed by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business as one operating segment and the Company operates in only one geographic region.
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying consolidated financial statements have been prepared under U.S. generally accepted accounting principles (“GAAP”) and include the accounts of the Company and its wholly owned subsidiary, Merrimack Pharmaceuticals (Bermuda) Ltd., which was merged with and into the Company during the third quarter of 2014. The Company also consolidates its majority owned subsidiary, Silver Creek Pharmaceuticals, Inc. (“Silver Creek”). All intercompany transactions and balances have been eliminated in consolidation. 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 a loss from discontinued operations, net of tax in the condensed consolidated statements of operations for all periods presented. In addition, in the condensed consolidated balance sheet as of December 31, 2016, 2015 and 2014, the assets and liabilities held for sale have been presented separately. For additional information, see Note 2, “Discontinued Operations.” 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 the 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 15, “Stock-Based Compensation.”
Use of Estimates	Use of Estimates GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues, expenses and related disclosures. The Company bases estimates and judgments on historical experience and on various other factors that it believes to be reasonable under the circumstances. The most significant estimates in these consolidated financial statements include, but may not be limited to, revenue recognition, including the estimated percentage of billable expenses in any particular budget period, periods of meaningful use of licensed products, estimated service periods and services to be completed under a collaboration, estimates used in accounting for revenue separability and recognition, estimates of discounts and allowances related to commercial sales of ONIVYDE, estimates utilized in the valuation of inventory, useful lives with respect to long-lived assets and intangible assets, accounting for stock-based compensation, contingencies, intangible assets, goodwill, in-process research and development (“IPR&D”), tax valuation reserves and accrued expenses. The Company’s actual results may differ from these estimates under different assumptions or conditions. The Company evaluates its estimates on an ongoing basis. Changes in estimates are reflected in reported results in the period in which they become known by the Company’s management.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents are short-term, highly liquid investments with original maturities of three months or less at the date of purchase. Investments qualifying as cash equivalents primarily consist of money market funds, commercial paper, corporate notes and bonds and certificates of deposit. Cash accounts with any type of restriction are classified as restricted cash. If restrictions are expected to be lifted in the next twelve months, the restricted cash account is classified as current. As of December 31, 2016 and 2015, the Company recorded restricted cash of $0.8 million and $0.7 million, respectively, which was primarily related to the Company’s facility lease.
Marketable Securities	Marketable Securities The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available-for-sale. Available-for-sale securities may consist of U.S. government agencies securities, commercial paper, corporate notes and bonds and certificates of deposit, which are maintained by an investment manager. Available-for-sale securities are carried at fair value, with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ deficit until realized. To determine whether an other-than-temporary impairment exists, the Company performs an analysis to assess whether it intends to sell, or whether it would more likely than not be required to sell, the security before the expected recovery of the amortized cost basis. Where the Company intends to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary and the full amount of the unrealized loss is recognized on the statement of operations and comprehensive loss as an other-than-temporary impairment charge. When this is not the case, the Company performs additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where the Company does not expect to receive cash flows, based on using a single best estimate, sufficient to recover the amortized cost basis of a security and amount of the loss recognized in other income (expense). Realized gains and losses are recognized in interest income. Any premium or discount arising at purchase is amortized and/or accreted to interest income.
Inventory	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 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 Intangible Assets Goodwill and indefinite-lived intangible assets, including IPR&D assets, are evaluated for impairment on an annual basis or more frequently if an indicator of impairment is present. The Company performs its annual goodwill and IPR&D impairment evaluations on August 31 st When performing an evaluation of goodwill impairment, the Company has the option to first assess qualitative factors to determine whether it is necessary to perform the quantitative two-step impairment test. If the Company elects this option and finds, as a result of the qualitative assessment, that it is more likely than not that the fair value of the reporting unit is less than its carrying amount, the quantitative two-step impairment test is required; otherwise, further testing is not required. This requires the Company to assess the impact of significant events, milestones and changes to expectations and activities that may have occurred since the last impairment evaluation. Significant changes to these estimates, judgments and assumptions could materially change the outcome of the impairment assessment. Alternatively, the Company may elect to not first assess qualitative factors and immediately perform the quantitative two-step impairment test. If such an election occurs, in the first step, the fair value of the Company’s reporting unit is compared to the carrying value. If the carrying value of the net assets assigned to the reporting unit exceeds the fair value of the reporting unit, then the second step of the impairment test is performed in order to determine the implied fair value of the reporting unit’s goodwill. If the carrying value of the reporting unit’s goodwill exceeds the implied fair value, then the Company would record an impairment loss equal to the difference. As described above, the Company operates in one operating segment, which is considered the only reporting unit. The Company commences amortization of indefinite-lived intangible assets, such as IPR&D, once the associated research and development efforts have been completed. The Company amortizes these product-related intangible assets over their estimated useful lives, and amortization expense is recorded as a component of “Cost of revenues.” The Company amortizes other definite-lived assets, such as core technology, over their estimated useful lives as a component of “Research and development expenses.” Definite-lived intangible assets are evaluated for impairment whenever events or circumstances indicate that the carrying value may not be fully recoverable. 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	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 Non-controlling interest represents the non-controlling stockholders’ proportionate share of preferred stock and net loss of the Company’s majority owned consolidated subsidiary, Silver Creek. The non-controlling stockholders’ proportionate share of the preferred stock in Silver Creek is reflected as non-controlling interest in the Company’s consolidated balance sheets as a component of mezzanine equity.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; delivery has occurred or services have been rendered; the price to the customer is fixed or determinable; and collectability is reasonably assured. Product Revenues, Net The Company sells ONIVYDE to a limited number of specialty pharmaceutical distributors in the United States (collectively, its “Distributors”). The Company’s Distributors subsequently resell the products to healthcare providers. The Company recognizes revenue on product sales when title and risk of loss have passed to the Distributor, which is typically upon delivery. Product revenues are recorded net of applicable reserves for discounts and allowances. As a result of the Asset Sale, all product revenue relates to the Commercial Business and has 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 estimates its net product revenues by deducting from its gross product revenues trade allowances, estimated contractual discounts, estimated Medicaid rebates, estimated reserves for product returns and estimated costs of other incentives offered to patients. These discounts and allowances are based on estimates of the amounts earned or to be claimed on the related sales. The Company’s estimates take into consideration its historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted Distributor buying and payment patterns. Actual amounts may ultimately differ from the Company’s estimates. If actual results vary, the Company will adjust these estimates, which could have an effect on earnings in the period of adjustment. Product revenue reserves and allowances that reduce gross revenue are categorized as follows: Trade Allowances: The Company pays fees to its Distributors for providing certain data to the Company as well as for maintaining contractual inventory and service levels. These trade allowances are recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized. Rebates and Chargeback Discounts: The Company is subject to discount obligations under state Medicaid programs and the Public Health Service 340B Drug Pricing Program, contracts with Federal government entities purchasing via the Federal Supply Schedule and various private organizations, such as group purchasing organizations (collectively, its “Third-party Payors”). The Company estimates the rebates and chargeback discounts it will provide to Third-party Payors, based upon its estimated payor mix, and deducts these estimated amounts from its gross product revenues at the time revenue is recognized. Chargeback discounts are processed when the Third-party Payor purchases the product at a discount from the Distributor, who then in turn charges back to the Company the difference between the price initially paid by the Distributor and the discounted price paid by the Third-party Payor. These chargeback discounts are recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized. Rebates that are invoiced directly to the Company are recorded as accrued liabilities on the consolidated balance sheet at the time revenue is recognized. Product Returns: An allowance for product returns is established for returns expected to be made by Distributors and is recorded at the time revenue is recognized, resulting in a reduction to product sales. In accordance with contractual terms, Distributors have the right to return unopened and undamaged product that is within a permissible number of months before and after the product’s expiration date, subject to contractual limitations. The Company has the ability to monitor inventory levels and the shelf life of product at Distributors and can contractually control the amount of inventory that is sold to Distributors. Based on inventory levels held by Distributors and the structure of the Company’s distribution model, the Company has concluded that it has the ability to reasonably estimate product returns at the time revenue is recognized. The Company’s estimated rate of return is based on historical rates of return for comparable oncology products. Other Incentives: The Company offers co-pay mitigation support to commercially insured patients. The Company’s co-pay mitigation program is intended to reduce each participating patient’s portion of the financial responsibility for a product’s purchase price to a specified dollar amount. Based upon the terms of the Company’s co-pay mitigation program, the Company estimates average co-pay mitigation amounts in order to establish a reserve for co-pay mitigation claims and deducts these estimated amounts from its gross product revenues at the later of the date that (i) the revenues are recognized or (ii) the incentive is offered. Claims under the Company’s co-pay mitigation program are subject to expiration. All product revenue recognized relates to the Commercial Business and is presented as income (loss) from discontinued operations, net of tax in the condensed consolidated statements of operations for all periods presented. All balance sheet accounts described above are included in the assets or liabilities for discontinued operation for all periods presented. License and Collaboration Revenues The Company enters into biopharmaceutical product development agreements with collaborative partners for the research and development of therapeutic and diagnostic products. The terms of the agreements may include nonrefundable signing and licensing fees, funding for research, development and manufacturing, milestone payments and royalties or profit-sharing on any product sales derived from collaborations. These multiple-element arrangements are analyzed to determine whether the deliverables can be separated or whether they must be accounted for as a single unit of accounting. The revenue recognition guidance related to multiple-element arrangements requires entities to separate and allocate consideration in a multiple-element arrangement according to the relative selling price of each deliverable. The fair value of deliverables under the arrangement may be derived using a best estimate of selling price if vendor specific objective evidence and third-party evidence are not available. Deliverables under the arrangement will be separate units of accounting provided that a delivered item has value to the customer on a stand-alone basis and if the arrangement does not include a general right of return relative to the delivered item and delivery or performance of the undelivered item is considered probable and substantially in the control of the vendor. In September 2014, the Company entered into a license and collaboration agreement (the “Baxalta Agreement”) with Baxter International Inc., Baxter Healthcare Corporation and Baxter Healthcare SA (collectively, “Baxter”) for the development and commercialization of ONIVYDE outside of the United States and Taiwan (the “Licensed Territory”). In connection with Baxter International Inc.’s separation of the Baxalta business, the Baxalta Agreement was assigned to Baxalta Incorporated, Baxalta US Inc. and Baxalta GmbH (collectively, “Baxalta”) during the second quarter of 2015. The Baxalta Agreement was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements. The Company determined that the obligations under this agreement represent a single unit of accounting and that the agreement represents a services agreement. As a result, the Company has estimated the level of effort expected to be completed as a result of providing the identified deliverables and will recognize revenue related to the agreement based on proportional performance as effort is completed over the expected services period. The Company also entered into a collaboration agreement with Watson Laboratories, Inc. (“Actavis”) in November 2013, which was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements. All operating results recognized related to the Baxalta Agreement and Actavis Agreement are presented as income (loss) from discontinued operations, net of tax in the condensed consolidated statements of operations for all periods presented. In addition, in the condensed consolidated balance sheet as of December 31, 2016, 2015 and 2014, the assets and liabilities related to the Baxalta Agreement and Actavis Agreement have been presented separately. Whenever the Company determines that an arrangement should be accounted for as a single unit of accounting, it determines the period over which the performance obligations would be performed and revenue would be recognized. If the Company cannot reasonably estimate the timing and the level of effort to complete its performance obligations under the arrangement, then revenue under the arrangement is recognized on a straight-line basis over the period the Company expects to complete its performance obligations. The Company’s collaboration agreements may include additional payments upon the achievement of performance-based milestones. As milestones are achieved, a portion of the milestone payment, equal to the percentage of the total time that the Company has performed the performance obligations to date divided by the total estimated time to complete the performance obligations, multiplied by the amount of the milestone payment, will be recognized as revenue upon achievement of such milestone. The remaining portion of the milestone will be recognized over the remaining performance period. Milestones that are tied to regulatory approvals are not considered probable of being achieved until such approval is received. Milestones tied to counterparty performance are not included in the Company’s revenue model until the performance conditions are met. Other Revenues The Company is a party to separate commercial supply agreements with Baxalta and PharmaEngine, Inc. (“PharmaEngine”) pursuant to which the Company supplies ONIVYDE to these entities. Revenue is recognized under these commercial supply arrangements when the counterparty takes delivery of the commercial supply product and when the other general revenue recognition criteria outlined above are met. The Company is also eligible to receive royalty revenues on Baxalta’s net sales of ONIVYDE in the Licensed Territory. The Company recognizes royalty revenues in the period that the related sales occur. All other revenue recognized relates to the Commercial Business and is presented as income (loss) from discontinued operations, net of tax in the condensed consolidated statements of operations for all periods presented.
Research and Development Expenses	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 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. 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	Stock-Based Compensation Expense The Company accounts for its stock-based compensation awards in accordance with ASC 718, Compensation – Stock Compensation 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 Comprehensive loss consists of net loss and unrealized gains and losses on available-for-sale marketable securities.
Other (Expense) Income, Net	Other (Expense) Income, Net The Company records income related to tax incentive awards, foreign currency gains and losses and other income or expense-related items as components of “Other (expense) income, net” within the consolidated statements of operations and comprehensive loss. The Company has been awarded tax incentives by the Massachusetts Life Sciences Center (“MLSC”), an independent agency of the Commonwealth of Massachusetts. These tax incentives require that the Company achieve certain hiring targets. Failure to maintain the additional headcount in subsequent periods could require the Company to repay some or all of the incentives. The Company recognizes the benefit of these incentives on a straight-line basis over the five-year performance period of each award, beginning when the Company achieves the hiring goal target, with a cumulative catch-up recognized in the period that the hiring goal target is achieved. The Company received MLSC tax incentives in 2011, 2013, 2014 and 2015 totaling $3.8 million in the aggregate, allowing the Company to monetize approximately $3.4 million of state research and development tax credits. As a result of the October 2016 corporate restructuring described more fully in Note 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 $1.3 million. Such amounts have been classified as current liabilities as of December 31, 2016. The Company recognized $0.1 million, $0.7 million and $0.4 million in income related to these MLSC tax incentives during the years ended December 31, 2016, 2015 and 2014, respectively.
Income Taxes	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	Concentration of Credit Risk Financial instruments that subject the Company to credit risk consist primarily of cash, cash equivalents and marketable securities. The Company places its cash deposits in accredited financial institutions and, therefore, the Company’s management believes these funds are subject to minimal credit risk. The Company invests cash equivalents and marketable securities in money market funds, U.S. government agencies securities and various corporate debt securities. Credit risk in these securities is reduced as a result of the Company’s investment policy to limit the amount invested in any one issue or any single issuer and to only invest in high credit quality securities. The Company has no significant off-balance sheet concentrations of credit risk such as foreign currency exchange contracts, option contracts or other hedging arrangements. The Company also is subject to credit risk from its accounts receivable related to its product sales and collaborators. The Company evaluates the creditworthiness of each of its customers and has determined that all of its customers are creditworthy. To date, the Company has not experienced significant losses with respect to the collection of its accounts receivable. Gross revenues from each of the Company’s customers who individually accounted for 10% or more of total gross revenues for the years ended December 31, 2016, 2015 and 2014 consisted of the following: Years Ended December 31, 2016 2015 2014 Sanofi — — 90%
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers (Topic 606),” which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. This guidance was originally effective for interim and annual periods beginning after December 15, 2016 and allows for adoption using a full retrospective method, or a modified retrospective method. Early adoption was originally not permitted. Subsequent to the issuance of ASU 2014-09, the FASB also issued the following updates related to ASC 606, Revenue from Contracts with Customers: • In August 2015, the FASB issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date,” whereby the effective date for the new revenue standard was deferred by one year. As a result of ASU 2015-14, the new revenue standard is now effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017, and early adoption is now permitted for annual periods beginning after December 15, 2016, including interim periods within that annual period. • In March 2016, the FASB issued ASU 2016-08, “Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net),” to clarify the implementation guidance on principal versus agent considerations. • In April 2016, the FASB issued ASU 2016-10, “Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing,” to clarify the principle for determining whether a good or service is “separately identifiable” from other promises in the contract and to clarify the categorization of licenses of intellectual property. • In May 2016, the FASB issued ASU 2016-12, “Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Technical Expedients,” to clarify guidance on transition, determining collectibility, non-cash consideration and the presentation of sales and other similar taxes. • In December 2016, the FASB issued ASU 2016-20, “Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers,” that allows entities not to make qualitative disclosures about remaining performance obligations in certain cases, adds disclosure requirements for entities that elect certain optional exemptions and adds twelve additional technical corrections and improvements to the new revenue standard. The Company is currently evaluating the potential impact that the adoption of this guidance and the related transition guidance may have on the consolidated financial statements, including the adoption method to be utilized. In August 2014, the FASB issued ASU 2014-15, “Presentation of Financial Statements – Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern,” outlining management’s responsibility to perform interim and annual assessments of an entity’s ability to continue as a going concern within one year of the date the financial statements are issued and providing guidance on determining when and how to disclose going concern uncertainties in the financial statements. This guidance is effective for annual and interim reporting periods ending after December 15, 2016, and the Company adopted this guidance for the year ended December 31, 2016, as described more fully in Note 21, “Going Concern.” In January 2016, the FASB issued ASU 2016-01, “Financial Statements – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Liabilities,” which contains a number of provisions related to the measurement, presentation and disclosure of financial instruments. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual periods. Early adoption of this guidance is not permitted with the exception of certain specific presentation requirements that are not currently applicable to the Company. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance. In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842),” which supersedes all existing lease accounting guidance within ASC 840, Leases In March 2016, the FASB issued ASU 2016-06, “Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments,” which clarifies the requirements for assessing whether contingent call or put options that can accelerate the repayment of principal on debt instruments are clearly and closely related to their debt hosts. This guidance will be effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods, and early adoption is permitted. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance. In March 2016, the FASB issued ASU 2016-09, “Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” which simplifies several areas of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either liabilities or equity and classification of excess tax benefits on the statement of cash flows. This guidance also permits a new entity-wide accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur. This guidance will be effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods, and early adoption is permitted. An entity that elects early adoption must adopt all of the amendments in the same period. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments,” which represents a new credit loss standard that will change the impairment model for most financial assets and certain other financial instruments. Specifically, this guidance will require entities to utilize a new “expected loss” model as it relates to trade and other receivables. In addition, entities will be required to recognize an allowance for estimated credit losses on available-for-sale debt securities, regardless of the length of time that a security has been in an unrealized loss position. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments,” which is intended to reduce diversity in practice in how entities present certain types of cash transactions in the statement of cash flows. This guidance also clarifies how the predominance principle should be applied when classifying cash receipts and cash payments that have attributes of more than one class of cash flows. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption is permitted. An entity that elects early adoption must adopt all of the amendments in the same period. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance. In November 2016, the FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash,” which will require entities to show the change in the total of cash, cash equivalents, restricted cash and restricted cash equivalents within the statement of cash flows. As a result, entities will no longer separately present transfers between unrestricted cash and restricted cash. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption is permitted. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance. In January 2017, the FASB issued ASU 2017-04, “Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” which will eliminate the requirement to calculate the implied fair value of goodwill, commonly referred to as “Step 2” in the current goodwill impairment test. An entity will still have the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. This guidance will be effective for annual and interim impairment tests performed in annual reporting periods beginning after December 15, 2020, and early adoption is permitted for annual or interim impairment tests performed after January 1, 2017. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the consolidated financial statements. Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

Nature of the Business and Su29

Nature of the Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Schedule of Estimated Useful Lives of Property and Equipment Including Leasehold Improvements	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
Schedules of Concentration of Risk by Risk Factor	Gross revenues from each of the Company’s customers who individually accounted for 10% or more of total gross revenues for the years ended December 31, 2016, 2015 and 2014 consisted of the following: Years Ended December 31, 2016 2015 2014 Sanofi — — 90%

Discontinued Operations - Sal30

Discontinued Operations - Sale of Commercial Business (Tables)	12 Months Ended
	Dec. 31, 2016
Discontinued Operations And Disposal Groups [Abstract]
Schedule of Discontinued Operations and Assets Held for Sale	Discontinued operations for the years ended December 31, 2016, 2015 and 2014 includes the following: (in thousands) Years Ended December 31, 2016 2015 2014 Revenues: Product revenues, net $ 53,064 $ 4,328 $ — License and collaboration revenues 87,119 84,930 10,460 Other revenues 4,090 — — Total revenues 144,273 89,258 10,460 Costs and expenses: Cost of revenues 6,912 46 — Research and development expenses 51,352 39,955 35,185 Selling, general and administrative expenses 48,677 33,747 11,751 Restructuring expenses 146 — — Total costs and expenses 107,087 73,748 46,936 Other income and expenses: Interest expense (21,196 ) (463 ) — Income (loss) from discontinued operations $ 15,990 $ 15,047 $ (36,476 ) Income tax expense (13,224 ) (11,215 ) — Total income (loss) from discontinued operations $ 2,766 $ 3,832 $ (36,476 )
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 condensed consolidated balance sheets are as follows: (in thousands) December 31, 2016 December 31, 2015 Assets Current assets: Accounts receivable, net $ 17,194 $ 6,472 Inventory 14,554 3,717 Prepaid expenses and other current assets 1,547 1,273 Total current assets held for sale 33,295 11,462 Property and equipment, net 1,553 1,814 Intangible assets, net 3,977 4,555 Goodwill 3,605 3,605 Total long-term assets held for sale 9,135 9,974 Liabilities Current liabilities: Accounts payable, accrued expenses and other 21,312 15,343 Deferred revenues 36,226 50,137 Total current liabilities held for sale 57,538 65,480 Deferred revenues, net of current portion 25,673 51,197 Total long-term liabilities held for sale 25,673 51,197

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Schedule of Securities Excluded from Computation of Diluted Loss Per Share	Securities excluded from the calculation of diluted loss per share are shown in the chart below: Years Ended December 31, (in thousands) 2016 2015 2014 Common stock warrants — — 238 Outstanding options to purchase common stock 1,903 1,921 1,957 Conversion of the Convertible Notes 1,216 2,500 2,500

License and Collaboration Agr32

License and Collaboration Agreements (Tables)	12 Months Ended
	Dec. 31, 2016
Sanofi [Member]
Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements	The Company recognized no revenue under the Sanofi agreement during the years ended December 31, 2016 or 2015. During the year ended December 31, 2014, the Company recognized revenue based on the following components of the Sanofi agreement: (in thousands) Year Ended December 31, 2014 Upfront payment $ 39,306 Milestone payment 16,377 Development services 18,904 Manufacturing services and other 17,709 Total $ 92,296

Fair Value of Financial Instr33

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables summarize assets and liabilities measured at fair value on a recurring basis as of December 31, 2016 and 2015 and the input categories associated with those assets and liabilities: December 31, 2016 (in thousands) Level 1 Level 2 Level 3 Assets: Money market funds $ 12,373 $ — $ — Totals $ 12,373 $ — $ — Liabilities: Silver Creek warrant liability $ — $ — $ 1,499 Totals $ — $ — $ 1,499 December 31, 2015 (in thousands) Level 1 Level 2 Level 3 Assets: Money market funds $ 704 $ — $ — Totals $ 704 $ — $ —

Intangible Assets, Net (Tables)

Intangible Assets, Net (Tables)	12 Months Ended
	Dec. 31, 2016
Goodwill And Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	The Company did not have any intangible assets as of December 31, 2016, and the intangible assets as of December 31, 2015 consisted of the following: December 31, 2015 (in thousands) Gross C Accumulated Amortization Net Carrying Value IPR&D 2,800 — 2,800

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net as of December 31, 2016 and 2015 consisted of the following: December 31, (in thousands) 2016 2015 Lab equipment $ 17,537 $ 16,325 IT equipment 8,509 7,733 Leasehold improvements 20,633 20,507 Furniture and fixtures 626 635 Construction in process 378 2,243 Total property and equipment, gross 47,683 47,443 Less: Accumulated depreciation (33,471 ) (27,342 ) Total property and equipment, net $ 14,212 $ 20,101

Accounts Payable, Accrued Exp36

Accounts Payable, Accrued Expenses and Other (Tables)	12 Months Ended
	Dec. 31, 2016
Payables And Accruals [Abstract]
Schedule of Accounts Payable, Accrued Expenses and Other	Accounts payable, accrued expenses and other as of December 31, 2016 and 2015 consisted of the following: December 31, (in thousands) 2016 2015 Accounts payable $ 2,692 $ 3,848 Accrued goods and services 7,534 8,283 Accrued clinical trial costs 8,776 9,170 Accrued drug purchase costs 480 6,620 Accrued payroll and related benefits 3,394 5,313 Accrued restructuring expenses 774 — Accrued interest 2,100 3,041 Accrued dividends payable 19 19 Silver Creek warrant liability 1,499 — Deferred tax incentives 1,402 445 Total accounts payable, accrued expenses and other $ 28,670 $ 36,739

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule of Future Minimum Payments under the Loans Payable	Future minimum payments under outstanding borrowings as of December 31, 2016 are as follows: (in thousands) Convertible Notes 2017 $ 2,736 2018 2,736 2019 2,736 2020 63,527 2021 and thereafter — Total 71,735 Less interest (10,943 ) Less unamortized discount (13,842 ) Less current portion — Long-term debt $ 46,950

Restructuring Activities (Table

Restructuring Activities (Tables)	12 Months Ended
	Dec. 31, 2016
Restructuring And Related Activities [Abstract]
Summary of Charges Related to Restructuring Activities	The following table summarizes the charges related to the restructuring activities as of December 31, 2016: (in thousands) Expenses Less: Payments Less: Non-Cash Expenses Accrued Restructuring Expenses at December 31, 2016 Severance, benefits and related costs due to workforce reduction $ 5,710 $ (3,565 ) $ (1,371 ) $ 774 Totals $ 5,710 $ (3,565 ) $ (1,371 ) $ 774

Common Stock Warrants (Tables)

Common Stock Warrants (Tables)	12 Months Ended
	Dec. 31, 2016
Text Block [Abstract]
Schedule of Common Stock Warrant Activity of the Company	The following is a description of the common stock warrant activity of the Company: (in thousands, except per share amounts) Warrants for the Purchase of Common Weighted Average Exercise Price Balance at December 31, 2013 278 $ 30.50 Exercised (40 ) $ 33.80 Balance at December 31, 2014 238 $ 30.00 Exercised (235 ) $ 30.00 Cancelled (3 ) $ 30.00 Balance at December 31, 2015 — $ —

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees	The fair value of stock options granted to employees during the years ended December 31, 2016, 2015 and 2014 was estimated at the date of grant using the following assumptions: Years Ended December 31, 2016 2015 2014 Risk-free interest rate 1.1 – 2.0% 1.5 – 1.8% 1.6 – 2.0% Expected dividend yield 0% 0% 0% Expected term 5.0 – 5.8 years 5.0 – 5.9 years 5.0 – 5.9 years Expected volatility 67 – 69% 66 – 67% 64 – 72%
Schedule of Recognized Stock-Based Compensation Expense	The Company recognized stock-based compensation expense during the years ended December 31, 2016, 2015 and 2014 as follows: Years Ended December 31, (in thousands) 2016 2015 2014 Employee awards: Research and development expense $ 6,083 $ 7,711 $ 6,434 General and administrative expense 4,685 5,392 5,276 Restructuring expense 1,371 — — Stock-based compensation expense for employee awards 12,139 13,103 11,710 Stock-based compensation expense for non-employee awards 1 58 268 Total stock-based compensation expense $ 12,140 $ 13,161 $ 11,978
Summary of Stock Option Activity	The following table summarizes stock option activity during the year ended December 31, 2016: (in thousands, except per share amounts) Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Outstanding at December 31, 2015 1,921 $ 57.20 6.24 $ 47,963 Granted 426 $ 55.70 Exercised (196 ) $ 32.90 Forfeited (249 ) $ 70.40 Outstanding at December 31, 2016 1,902 $ 57.70 5.97 $ 7,564 Vested and expected to vest at December 31, 2016 1,879 $ 57.60 5.93 $ 7,564 Exercisable at December 31, 2016 1,497 $ 54.90 5.24 $ 7,564

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate	A reconciliation of the Company’s effective tax rate to the statutory federal income tax rate is as follows: Years Ended December 31, 2016 2015 2014 Federal income tax at statutory federal rate 35.0 % 35.0 % 35.0 % State taxes 0.6 1.2 3.7 Permanent differences (6.3 ) (2.4 ) (6.5 ) Stock-based compensation (1.5 ) (1.0 ) (2.7 ) Tax credits 12.6 9.0 24.1 Change in deferred state tax rate (0.3 ) (1.9 ) — Other 3.7 (0.5 ) 1.8 Change in valuation allowance (36.0 ) (32.5 ) (55.4 ) Total 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, 2016 and 2015 are as follows: December 31, (in thousands) 2016 2015 Deferred tax assets Net operating losses $ 194,027 $ 182,992 Capitalized research and development expenses 15,854 21,444 Credit carryforwards 144,823 93,113 Depreciation 2,557 2,128 Deferred compensation 12,463 11,664 Accrued expenses 3,601 1,807 Deferred revenue 21,935 10,999 Other temporary differences 25,276 17,235 Total gross deferred tax assets 420,536 341,382 Valuation allowance (414,558 ) (326,577 ) Net deferred tax assets 5,978 14,805 Deferred tax liabilities Intangible assets (1,428 ) (2,667 ) Debt discount (4,550 ) (12,138 ) Net deferred taxes $ — $ —
Schedule of Changes in the Valuation Allowance	The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2016, 2015 and 2014 was as follows: (in thousands) Balance at Beginning of Period Additions Deductions Balance at End of Period December 31, 2014 $ 207,304 $ 50,185 $ — $ 257,489 December 31, 2015 257,489 69,088 — 326,577 December 31, 2016 326,577 87,981 — 414,558

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases	Future minimum lease payments to be made by the Company under non-cancelable operating leases as of December 31, 2016 are as follows: Years ended December 31, (in 2017 $ 8,108 2018 8,102 2019 4,082 Total future minimum lease payments $ 20,292

Selected Quarterly Financial 43

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following table contains quarterly financial information for 2016 and 2015. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands, except per share data) 2016 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 ) 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 income (loss) per common share Net loss from continuing operations (3.23 ) (4.07 ) (2.06 ) (2.93 ) Net income (loss) 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 ) First Quarter Second Quarter Third Quarter Fourth Quarter (in thousands, except per share data) 2015 Research and development expenses 26,435 26,479 29,944 38,175 General and administrative expenses 4,712 5,824 5,989 7,523 Net loss from continuing operations (35,553 ) (25,426 ) (40,040 ) (50,600 ) Income from discontinued operations, net of tax 1,121 2,525 (2,346 ) 2,532 Net loss (34,432 ) (22,901 ) (42,386 ) (48,068 ) Net loss attributable to Merrimack Pharmaceuticals, Inc. (34,759 ) (22,778 ) (42,594 ) (47,826 ) Basic and dilutive net income (loss) per common share Net loss from continuing operations (3.35 ) (2.30 ) (3.58 ) (4.38 ) Net income (loss) from discontinued operations, net of tax 0.10 0.23 (0.21 ) 0.22 Net loss per share (3.24 ) (2.07 ) (3.79 ) (4.16 )

Nature of the Business and Su44

Nature of the Business and Summary of Significant Accounting Policies - Additional Information (Detail)

Oct. 16, 2017USD ($)

Sep. 05, 2017shares

Aug. 11, 2017shares

Apr. 03, 2017USD ($)

Sep. 30, 2017USD ($)

Dec. 31, 2016USD ($)ProgramSegmentRegionshares

Dec. 31, 2015USD ($)shares

Dec. 31, 2014USD ($)

Jan. 07, 2017USD ($)

Jun. 30, 2016shares

Apr. 18, 2016shares

Apr. 13, 2016shares

Dec. 22, 2015

Dec. 31, 2013USD ($)

Jul. 31, 2013

Summary Of Significant Accounting Policies [Line Items]

Number of development programs active | Program

2

Unrestricted cash and cash equivalents

$ 21,524,000

$ 185,606,000

$ 35,688,000

$ 65,086,000

Aggregate principal amount outstanding redeemed

$ 40,000,000

Number of operating segments | Segment

1

Number of geographic regions | Region

1

Reverse stock split description

Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock

Common stock, shares issued | shares

13,020,000

11,587,000

Common stock, shares outstanding | shares

13,020,000

11,587,000

Common stock, shares authorized | shares

20,000,000

20,000,000

Preferred stock, shares issued | shares

0

0

Preferred stock, shares outstanding | shares

0

0

Original maturities

Three months or less

Restricted cash

$ 800,000

$ 700,000

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

1,300,000

Amount of benefit recognized

$ 100,000

$ 700,000

$ 400,000

2022 Notes [Member]

Summary Of Significant Accounting Policies [Line Items]

Interest rate (as a percent)

11.50%

Convertible Notes [Member]

Summary Of Significant Accounting Policies [Line Items]

Interest rate (as a percent)

4.50%

Reverse stock split, conversion ratio

0.1

Reverse stock split description

one-for-ten reverse stock split

Common stock, shares issued | shares

1,236,766

873,215

363,551

Minimum [Member]

Summary Of Significant Accounting Policies [Line Items]

Expected remaining maturities period of marketable securities classified as available-for-sale

3 months

Subsequent Event [Member]

Summary Of Significant Accounting Policies [Line Items]

Reverse stock split, conversion ratio

0.1

Common stock, shares issued | shares

13,280,000

132,800,000

Common stock, shares outstanding | shares

13,280,000

132,800,000

Number of fractional shares issued | shares

0

Common stock, shares authorized | shares

20,000,000

200,000,000

Preferred stock, shares issued | shares

0

Preferred stock, shares outstanding | shares

0

Subsequent Event [Member] | Convertible Notes [Member]

Summary Of Significant Accounting Policies [Line Items]

Interest rate (as a percent)

4.50%

Deposited into escrow account

$ 60,000,000

Subsequent Event [Member] | Asset Sale Agreement [Member]

Summary Of Significant Accounting Policies [Line Items]

Special cash dividend distributed

140,000,000

Subsequent Event [Member] | Asset Sale Agreement [Member] | 2022 Notes [Member]

Summary Of Significant Accounting Policies [Line Items]

Aggregate principal amount outstanding redeemed

$ 175,000,000

Interest rate (as a percent)

11.50%

Additional premium payment

$ 20,100,000

Subsequent Event [Member] | Ipsen [Member] | Asset Sale Agreement [Member]

Summary Of Significant Accounting Policies [Line Items]

Upfront cash payment received

575,000,000

$ 575,000,000

Working capital adjustments received

$ 4,900,000

$ 800,000

Subsequent Event [Member] | 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

450,000,000

Subsequent Event [Member] | Baxalta [Member] | License and Collaboration Agreements [Member]

Summary Of Significant Accounting Policies [Line Items]

Net milestone payments expected to be received

$ 33,000,000

Subsequent Event [Member] | 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 Su45

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

Nature of the Business and Su46

Nature of the Business and Summary of Significant Accounting Policies - Schedules of Concentration of Risk by Risk Factor - Gross Sales Revenue (Detail)	12 Months Ended
	Dec. 31, 2014
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Sanofi [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue	90.00%

Discontinued Operations - Sal47

Discontinued Operations - Sale of Commercial Business - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Apr. 03, 2017	Jan. 07, 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
Subsequent Event [Member] | 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
Subsequent Event [Member] | 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
Subsequent Event [Member] | 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
Subsequent Event [Member] | 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	$ 450,000,000

Discontinued Operations - Sal48

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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other income and expenses:
Income tax expense									$ (13,200)	$ (11,200)
Total income (loss) from discontinued operations	$ 6,464	$ (3,430)	$ 675	$ (943)	$ 2,532	$ (2,346)	$ 2,525	$ 1,121	2,766	3,832	$ (36,476)
Commercial Business [Member]
Revenues:
Product revenues, net									53,064	4,328
License and collaboration revenues									87,119	84,930	10,460
Other revenues									4,090
Total revenues									144,273	89,258	10,460
Costs and expenses:
Cost of revenues									6,912	46
Research and development expenses									51,352	39,955	35,185
Selling, general and administrative expenses									48,677	33,747	11,751
Restructuring expenses									146
Total costs and expenses									107,087	73,748	46,936
Other income and expenses:
Interest expense									(21,196)	(463)
Income (loss) from discontinued operations									15,990	15,047	(36,476)
Income tax expense									(13,224)	(11,215)
Total income (loss) from discontinued operations									$ 2,766	$ 3,832	$ (36,476)

Discontinued Operations - Sal49

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) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Total current assets held for sale	$ 33,295	$ 11,462
Total long-term assets held for sale	9,135	9,974
Current liabilities:
Total current liabilities held for sale	57,538	65,480
Total long-term liabilities held for sale	25,673	51,197
Commercial Business [Member]
Current assets:
Accounts receivable, net	17,194	6,472
Inventory	14,554	3,717
Prepaid expenses and other current assets	1,547	1,273
Total current assets held for sale	33,295	11,462
Property and equipment, net	1,553	1,814
Intangible assets, net	3,977	4,555
Goodwill	3,605	3,605
Total long-term assets held for sale	9,135	9,974
Current liabilities:
Accounts payable, accrued expenses and other	21,312	15,343
Deferred revenues	36,226	50,137
Total current liabilities held for sale	57,538	65,480
Deferred revenues, net of current portion	25,673	51,197
Total long-term liabilities held for sale	$ 25,673	$ 51,197

Consolidated Subsidiaries - Add

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

Net Loss Per Common Share - Add

Net Loss Per Common Share - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	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	$ 60,800,000

Net Loss Per Common Share - Sch

Net Loss Per Common Share - Schedule of Securities Excluded from Computation of Diluted Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common Stock Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted loss per share			238
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	1,903	1,921	1,957
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	2,500

License and Collaboration Agr53

License and Collaboration Agreements - Additional Information (Detail) - USD ($)	Apr. 03, 2017	Nov. 10, 2009	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Agreement termination scheduled date			Dec. 17, 2014
Assets maintained related to Sanofi Agreement			$ 81,483,000	$ 234,880,000
Liabilities maintained related to Sanofi Agreement			334,142,000	418,569,000
Ipsen [Member] | Asset Sale Agreement [Member] | Development and Commercialization Milestones [Member] | Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received	$ 33,000,000
Ipsen [Member] | Asset Sale Agreement [Member] | Sale Milestones in Major European Countries [Member] | Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	18,000,000
Ipsen [Member] | Asset Sale Agreement [Member] | Sale Milestones in Major Non-European and Non-Asian Country [Member] | Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	5,000,000
Ipsen [Member] | Asset Sale Agreement [Member] | Clinical Trials in Lung Cancer [Member] | Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	$ 10,000,000
Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront license fee received		$ 60,000,000
Milestone license fee received			25,000,000
Expected development period from the effective date of agreement		12 years
License and collaboration revenues			0	0
Assets maintained related to Sanofi Agreement			0	0
Liabilities maintained related to Sanofi Agreement			$ 0	$ 0
Sanofi [Member] | License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and collaboration revenues					$ 92,296,000
Recognized revenue related to excess spending					$ 5,800,000
Spending in excess of budget						$ 10,100,000

License and Collaboration Agr54

License and Collaboration Agreements - Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements (Detail) - Sanofi [Member] - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total	$ 0	$ 0
License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment			$ 39,306,000
Milestone payment			16,377,000
Development services			18,904,000
Manufacturing services and other			17,709,000
Total			$ 92,296,000

Fair Value of Financial Instr55

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

Fair Value of Financial Instr56

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 22, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Transfers between fair value measurement levels	$ 0	$ 0
Non-recurring fair value measurements		0
Senior Convertible Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Aggregate principal amount of outstanding debt	47,000,000
Senior Convertible Notes [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of debt	57,500,000
2022 Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of debt	167,000,000
Aggregate principal amount of outstanding debt	169,900,000
Aggregate principal amount of loan			$ 175,000,000
Interest rate (as a percent)			11.50%
IPR&D [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of assets	$ 0
Recurring Basis [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value		$ 0
Silver Creek [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Risk-free interest rate	2.30%
Expected dividend yield	0.00%
Expected volatility	61.70%
Expected term	6 years 10 months 25 days
Silver Creek [Member] | Series C Preferred Stock [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Warrants issued to purchase preferred stock, shares	1,900,000
Warrants to purchase preferred stock, value	$ 1,500,000

Marketable Securities - Additio

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

Intangible Assets, Net - Additi

Intangible Assets, Net - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Impairment charge		$ 2,800,000
Intangible assets, net	$ 0	0	$ 2,800,000
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. 6, 2009

Intangible Assets, Net - Schedu

Intangible Assets, Net - Schedule of Intangible Assets (Detail) $ in Thousands	Dec. 31, 2015USD ($)
IPR&D [Member]
Intangible Assets By Major Class [Line Items]
Indefinite-lived intangible asset	$ 2,800

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 47,683	$ 47,443
Less: Accumulated depreciation	(33,471)	(27,342)
Total property and equipment, net	14,212	20,101
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	17,537	16,325
IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	8,509	7,733
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	20,633	20,507
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	626	635
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 378	$ 2,243

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant and Equipment Useful Life and Values [Abstract]
Depreciation expense	$ 6,500	$ 4,800	$ 3,700
Charge related to disposal of property and equipment	$ 493	$ 4

Accounts Payable, Accrued Exp62

Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts Payable And Accrued Liabilities [Line Items]
Accounts payable	$ 2,692	$ 3,848
Accrued goods and services	7,534	8,283
Accrued clinical trial costs	8,776	9,170
Accrued drug purchase costs	480	6,620
Accrued payroll and related benefits	3,394	5,313
Accrued restructuring expenses	774
Accrued interest	2,100	3,041
Accrued dividends payable	19	19
Deferred tax incentives	1,402	445
Total accounts payable, accrued expenses and other	28,670	$ 36,739
Silver Creek [Member]
Accounts Payable And Accrued Liabilities [Line Items]
Warrant liability	$ 1,499

Borrowings - 2022 Notes - Addit

Borrowings - 2022 Notes - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 22, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Debt maturity date		Jul. 15, 2020
Interest expense		$ 22,449,000	$ 18,769,000	$ 18,230,000
Change of Control Event [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	101.00%
Asset Sale Event [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	100.00%
2022 Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 175,000,000
Interest rate (as a percent)	11.50%
Net proceeds from the debt issuance	$ 168,500,000
Debt issuance costs	900,000
Semi-annual installments of principal	$ 21,875,000
Debt maturity date	Dec. 15, 2022
Effective interest rate		12.32%
Interest expense		$ 20,900,000	$ 500,000
2022 Notes [Member] | Conversion Terms, Fundamental Changes [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest		100.00%

Borrowings - Convertible Notes

Borrowings - Convertible Notes - Additional Information (Detail)	Sep. 05, 2017	May 26, 2017	Apr. 18, 2016shares	Apr. 13, 2016USD ($)shares	Jul. 31, 2013USD ($)$ / shares	Jul. 31, 2013USD ($)$ / shares	Jun. 30, 2016USD ($)shares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)
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								13,020,000	11,587,000
Loss on extinguishment of debt								$ 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
Interest expense								$ 22,449,000	$ 18,769,000	$ 18,230,000
Convertible Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount					$ 125,000,000	$ 125,000,000
Net proceeds from the debt issuance						$ 120,600,000
Interest rate (as a percent)					4.50%	4.50%
Embedded conversion option					$ 53,800,000	$ 53,800,000
Underwriting discounts and commissions and offering expenses					4,400,000
Principal amount of convertible notes due 2020 converted into shares of common stock				$ 64,200,000
Conversion ratio, principal amount				$ 1,000	$ 1,000	$ 1,000
Conversion rate of common stock shares per $1,000 principal amount	23.5210	235.2112	136		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
Reduction in additional paid-in capital attributable to embedded conversion option							$ 39,800,000
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible					30 days
Convertibility of debt, closing price of stock test, percentage of stock price to conversion price for the notes that must be exceeded					130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period					5 days
Number of consecutive trading days before five consecutive business days during the note measurement period					5 days
Initial conversion price of shares (in dollars per share) | $ / shares					$ 6.25	$ 6.25
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								$ 22,700,000	$ 13,700,000	$ 13,700,000
Convertible Notes [Member] | Conversion Terms, Fundamental Changes [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest					100.00%
Convertible Notes [Member] | Conversion Terms, Event of Default [Member]
Debt Instrument [Line Items]
Percentage of principal amount due and payable upon event of default arising out of certain bankruptcy events					100.00%
Convertible Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible					20 days
Convertible Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Convertibility of debt, trading price of debt test, percentage of closing price of stock used in calculation					98.00%
Convertible Notes [Member] | Transaction Costs Incurred With Third Parties [Member]
Debt Instrument [Line Items]
Reduction in additional paid-in capital								200,000
Convertible Notes [Member] | Interest Expense [Member] | Transaction Costs Incurred With Third Parties [Member]
Debt Instrument [Line Items]
Transaction costs related to conversion of convertible notes due 2020 incurred and paid								$ 200,000

Borrowings - Loan Agreement - A

Borrowings - Loan Agreement - Additional Information (Detail) - USD ($)	Feb. 25, 2015	Nov. 06, 2014	Dec. 22, 2015	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Nov. 30, 2012
Schedule Of Debt Instruments [Line Items]
Extension period for interest-only payment		4 months
Repayment of notes				$ 40,000,000
Interest expense					$ 22,449,000	$ 18,769,000	$ 18,230,000
2022 Notes [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount of loan			$ 175,000,000
Debt issuance costs			$ 900,000
Interest expense					20,900,000	500,000
2022 Notes [Member] | Modified Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Unamortized debt issuance costs				$ 300,000		300,000
Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Discount on loan recorded as a non-current liability to be paid upon full repayment or maturity of the loans					1,200,000
Hercules [Member]
Schedule Of Debt Instruments [Line Items]
Initial debt discount					1,600,000
Interest expense					$ 0	5,400,000	$ 4,700,000
Hercules [Member] | 2022 Notes [Member] | Modified Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Debt issuance costs						$ 900,000
Hercules [Member] | Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount of loan	$ 40,000,000							$ 40,000,000
Outstanding principal balance repayment start date	Jun. 1, 2016
Outstanding principal balance repayment end date	Nov. 1, 2018
Extended maturity period on principal payment	6 months

Borrowings - Credit Facility -

Borrowings - Credit Facility - Additional Information (Detail) - BioPharma Credit Investments IV Sub, LP (?Pharmakon?) [Member] - Credit Agreement [Member] - USD ($)	12 Months Ended
	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

Borrowings - Silver Creek Conve

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

Borrowings - Schedule of Future

Borrowings - Schedule of Future Minimum Payments under the Loans Payable (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 216,861	$ 257,655
Convertible Notes [Member]
Debt Instrument [Line Items]
2,017	2,736
2,018	2,736
2,019	2,736
2,020	63,527
Loans payable, gross including contractual interest	71,735
Less interest	(10,943)
Less unamortized discount	(13,842)
Long-term debt	$ 46,950

Restructuring Activities - Addi

Restructuring Activities - Additional Information (Detail) - USD ($) $ in Thousands	Oct. 03, 2016	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016
Restructuring Cost And Reserve [Line Items]
Reduction in headcount, percent	22.00%
Restructuring activity, announcement date				Oct. 3, 2016
Restructuring expenses		$ 4,901	$ 809	$ 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.
Stock-based Compensation Expense, Contractual Termination Benefits and One-time Employee Termination Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses				$ 5,700

Restructuring Activities - Summ

Restructuring Activities - Summary of Charges Related to Restructuring Activities (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016
Restructuring Cost And Reserve [Line Items]
Expenses	$ 4,901	$ 809	$ 5,710
Less: Payments			(3,565)
Less: Non-Cash Expenses			(1,371)
Accrued Restructuring Expenses	774		774
Severance Benefits and Related Costs Due to Workforce Reduction [Member]
Restructuring Cost And Reserve [Line Items]
Expenses			5,710
Less: Payments			(3,565)
Less: Non-Cash Expenses			(1,371)
Accrued Restructuring Expenses	$ 774		$ 774

Common Stock Warrants - Schedul

Common Stock Warrants - Schedule of Common Stock Warrant Activity of the Company (Detail) - Common Stock Warrant [Member] - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Beginning Balance	238	278
Exercised (in shares)	(235)	(40)
Cancelled (in shares)	(3)
Ending Balance		238
Beginning Balance	$ 30	$ 30.50
Exercised (per share)	30	33.80
Cancelled (per share)	$ 30
Ending Balance		$ 30

Common Stock Warrants - Additio

Common Stock Warrants - Additional Information (Detail) - Common Stock Warrant [Member] - shares	Dec. 31, 2015	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Number of warrants cashless exercised	229,500	7,500
Number of common stock issued as a result of cashless exercise of warrants	169,500	3,800

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - USD ($)	Jul. 13, 2015	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2016
Class of Stock [Line Items]
Net proceeds from issuance of common stock after deducting commissions and offering expenses			$ 38,560,000
Common stock, shares issued			11,587,000	13,020,000
Common stock, shares authorized			20,000,000	20,000,000
Common stock, par value			$ 0.01	$ 0.01
Common stock, shares outstanding			11,587,000	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 - Addi

Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions	Aug. 11, 2017shares	Feb. 29, 2016shares	Feb. 28, 2015shares	Mar. 31, 2014shares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares	Dec. 31, 2014USD ($)$ / sharesshares	Sep. 05, 2017shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reverse stock split description					Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock
Common stock, shares issued					13,020,000	11,587,000
Common stock, shares outstanding					13,020,000	11,587,000
Common stock, shares authorized					20,000,000	20,000,000
Preferred stock, shares issued					0	0
Preferred stock, shares outstanding					0	0
Number of Options, Granted					426,000
Weighted-average grant date fair value per share of stock options | $ / shares					$ 33.20	$ 58	$ 34.10
Aggregate intrinsic value of options exercised | $					$ 5.6	$ 30.9	$ 19.8
Unrecognized stock-based compensation expense related to nonvested stock options | $					$ 12.7
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized					1 year 8 months 12 days
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term					10 years
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reverse stock split, conversion ratio	0.1
Common stock, shares issued	132,800,000							13,280,000
Common stock, shares outstanding	132,800,000							13,280,000
Common stock, shares authorized	200,000,000							20,000,000
Number of fractional shares issued								0
Preferred stock, shares issued								0
Preferred stock, shares outstanding								0
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)					500,000
Number of Options, Granted					400,000	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 - Sche

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

Stock-Based Compensation - Sc76

Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 12,139	$ 13,103	$ 11,710
Stock-based compensation expense for non-employee awards	1	58	268
Total stock-based compensation expense	12,140	13,161	11,978
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	6,083	7,711	6,434
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	4,685	$ 5,392	$ 5,276
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 - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Options, Outstanding, Beginning balance	1,921
Number of Options, Granted	426
Number of Options, Exercised	(196)
Number of Options, Forfeited	(249)
Number of Options, Outstanding, Ending balance	1,902	1,921
Number of Options, Vested and expected to vest	1,879
Number of Options, Exercisable	1,497
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 57.20
Weighted-Average Exercise Price, Granted	55.70
Weighted-Average Exercise Price, Exercised	32.90
Weighted-Average Exercise Price, Forfeited	70.40
Weighted-Average Exercise Price, Outstanding, Ending balance	57.70	$ 57.20
Weighted-Average Exercise Price, Vested and expected to vest	57.60
Weighted-Average Exercise Price, Exercisable	$ 54.90
Weighted-Average Remaining Contractual Term	5 years 11 months 19 days	6 years 2 months 27 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	5 years 11 months 5 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 2 months 27 days
Aggregate Intrinsic Value, Outstanding	$ 7,564	$ 47,963
Aggregate Intrinsic Value, Vested and expected to vest	7,564
Aggregate Intrinsic Value, Exercisable	$ 7,564

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Income tax benefit	$ 13,224	$ 11,215
Income tax expense (benefit) in discontinued operations	13,200	$ 11,200
Federal and state net operating loss carryforwards relate to deductions for stock option compensation	39,200
Federal Orphan Drug Credits	106,400
Federal [Member]
Operating Loss Carryforwards [Line Items]
NOL	542,700
Federal [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	27,300
State [Member]
Operating Loss Carryforwards [Line Items]
NOL	367,400
Federal and state net operating loss carryforwards relate to deductions for stock option compensation	25,200
State [Member] | Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	16,300
State [Member] | Investment [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 800

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal income tax at statutory federal rate	35.00%	35.00%	35.00%
State taxes	0.60%	1.20%	3.70%
Permanent differences	(6.30%)	(2.40%)	(6.50%)
Stock-based compensation	(1.50%)	(1.00%)	(2.70%)
Tax credits	12.60%	9.00%	24.10%
Change in deferred state tax rate	(0.30%)	(1.90%)
Other	3.70%	(0.50%)	1.80%
Change in valuation allowance	(36.00%)	(32.50%)	(55.40%)
Total	7.80%	6.90%

Income Taxes - Schedule of Temp

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

Income Taxes - Schedule of Chan

Income Taxes - Schedule of Changes in the Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 326,577	$ 257,489	$ 207,304
Additions	87,981	69,088	50,185
Balance at end of period	$ 414,558	$ 326,577	$ 257,489

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	May 31, 2016ft²	Dec. 31, 2016USD ($)ft²	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Operating Leased Assets [Line Items]
Description of operating lease amendment		The Amended Lease will terminate on June 30, 2019, but the Company retains an option to renew the Amended Lease with respect to all of the leased space for an additional period of five years.
Aggregate space that the entity will lease under the amended lease agreement | ft²		167,000
Sublease Agreement [Member]
Operating Leased Assets [Line Items]
Description of operating lease amendment		The Sublease terminates on December 31, 2017, but may be extended through June 30, 2019 if mutually agreed upon by the Company and the subtenant.
Area of office and lab | ft²	8,143
Lease expiration date	Dec. 31, 2017
Lease extended date	Jun. 30, 2019
Operating leases, future minimum rental payments receivable		$ 0.6
Total rent expense		5	$ 4.3	$ 3.4
July 31, 2015 Amendment [Member]
Operating Leased Assets [Line Items]
Aggregate landlord reimbursable tenant improvements received under the existing lease and the lease amendment		$ 9.5

Commitments and Contingencies83

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,017	$ 8,108
2,018	8,102
2,019	4,082
Total future minimum lease payments	$ 20,292

Related Party Transactions - Ad

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

Retirement Plan - Additional In

Retirement Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Company's contributions to 401(k) defined contribution savings plan	$ 1.3	$ 1.1	$ 0.8

Selected Quarterly Financial 86

Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Research and development expenses	$ 25,621	$ 28,247	$ 27,695	$ 28,002	$ 38,175	$ 29,944	$ 26,479	$ 26,435	$ 109,565	$ 121,033	$ 103,310
General and administrative expenses	11,014	6,448	8,138	6,452	7,523	5,989	5,824	4,712	32,052	24,048	18,766
Restructuring expenses	4,901	809							5,710
Loss from continuing operations	(40,091)	(26,845)	(51,633)	(37,715)	(50,600)	(40,040)	(25,426)	(35,553)	(156,284)	(151,619)	(47,083)
Income (loss) from discontinued operations, net of tax	6,464	(3,430)	675	(943)	2,532	(2,346)	2,525	1,121	2,766	3,832	(36,476)
Net loss	(33,627)	(30,275)	(50,958)	(38,658)	(48,068)	(42,386)	(22,901)	(34,432)	(153,518)	(147,787)	(83,559)
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$ (32,449)	$ (30,068)	$ (50,750)	$ (38,473)	$ (47,826)	$ (42,594)	$ (22,778)	$ (34,759)	$ (151,740)	$ (147,957)	$ (83,291)
Basic and dilutive net income (loss) per common share
Net loss from continuing operations	$ (2.93)	$ (2.06)	$ (4.07)	$ (3.23)	$ (4.38)	$ (3.58)	$ (2.30)	$ (3.35)	$ (12.33)	$ (13.63)	$ (4.49)
Net income (loss) from discontinued operations, net of tax	0.43	(0.27)	0.05	(0.08)	0.22	(0.21)	0.23	0.10	0.22	0.34	(3.49)
Net loss per share	$ (2.50)	$ (2.33)	$ (4.02)	$ (3.31)	$ (4.16)	$ (3.79)	$ (2.07)	$ (3.24)	$ (12.11)	$ (13.29)	$ (7.98)

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) shares in Thousands	Nov. 14, 2017USD ($)	Oct. 13, 2017USD ($)$ / shares	Feb. 23, 2017	Feb. 06, 2017USD ($)shares	Jan. 09, 2017USD ($)Employee	Jan. 07, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)shares	Nov. 10, 2017USD ($)	Apr. 03, 2017USD ($)
Subsequent Event [Line Items]
Restructuring activity, announcement date									Oct. 3, 2016
Restructuring expenses							$ 4,901,000	$ 809,000	$ 5,710,000
Restructuring activities, description									One-time employee termination benefits were comprised of severance, benefits and related costs, all of which resulted in cash expenditures during the third and fourth quarters of 2016.
Option grant to purchase common stock | shares									426
Convertible Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount of outstanding debt							$ 60,800,000		$ 60,800,000
BioPharma Credit Investments IV Sub, LP (?Pharmakon?) [Member] | Credit Agreement [Member]
Subsequent Event [Line Items]
Credit facility, expiration date									Apr. 27, 2017
Chief Executive Officer [Member]
Subsequent Event [Line Items]
Employment agreement description									Dr. Peters will receive an annual base salary of $700,000 and is eligible for an annual bonus of up to 65% of his base salary. Dr. Peters also received a one-time signing bonus of $900,000. Subject to the further approval of the Company’s Board of Directors, the Company will also grant Dr. Peters an option to purchase a number of shares of the Company’s common stock equal to the lesser of (i) such number of shares that has a target grant date fair value of $3.5 million and (ii) 2.0 million shares, with an exercise price per share equal to the fair market value of the Company’s common stock on the date of grant.
Option vesting description									The option will vest over four years at the rate of 25% on February 6, 2018 and the remainder in equal quarterly installments over the following three years.
January 2017 Corporate Restructuring [Member]
Subsequent Event [Line Items]
Restructuring activity, announcement date									Jan. 9, 2017
Restructuring and related activities, completion date									Mar. 10, 2017
January 2017 Corporate Restructuring [Member] | One-time Employee Termination Benefits [Member]
Subsequent Event [Line Items]
Restructuring activities, description									one-time employee termination benefits are comprised of severance, benefits and related costs, all of which are expected to result in cash expenditures. The specific timing of the incurrence and payment of these restructuring expenses is dependent upon the timing of the closing of the asset sale.
Asset Sale Agreement [Member]
Subsequent Event [Line Items]
Assets sales termination fee description									The termination fee will also be payable if the Asset Sale Agreement is terminated because the Company’s stockholders did not vote to adopt the Asset Sale Agreement and, prior to such termination, a proposal to acquire at least 50% of the consolidated assets of the Company with respect to the Commercial Business or at least 50% of the Company’s voting securities has been publicly disclosed and the Company enters into a definitive agreement with respect to such proposal within 12 months after such termination, which is subsequently consummated.
Subsequent Event [Member] | BioPharma Credit Investments IV Sub, LP (?Pharmakon?) [Member] | Credit Agreement [Member]
Subsequent Event [Line Items]
Credit facility, expiration date			Apr. 27, 2017
Subsequent Event [Member] | Chief Executive Officer [Member]
Subsequent Event [Line Items]
Annual base salary				$ 700,000
One-time signing bonus				900,000
Target grant date fair value				$ 3,500,000
Option grant to purchase common stock | shares				2,000
Subsequent Event [Member] | Chief Executive Officer [Member] | Tranche 1 [Member]
Subsequent Event [Line Items]
Options vesting period				4 years
Option vesting percentage				25.00%
Option vesting date				Feb. 6, 2018
Subsequent Event [Member] | Chief Executive Officer [Member] | Tranche 2 [Member]
Subsequent Event [Line Items]
Remainder period for vesting option				3 years
Subsequent Event [Member] | January 2017 Corporate Restructuring [Member]
Subsequent Event [Line Items]
Restructuring and related cost, number of expected employees after headcount reduction | Employee					80
Subsequent Event [Member] | Maximum [Member] | Chief Executive Officer [Member]
Subsequent Event [Line Items]
Percentage of eligible annual bonus on base salary				65.00%
Subsequent Event [Member] | Maximum [Member] | January 2017 Corporate Restructuring [Member] | One-time Employee Termination Benefits [Member]
Subsequent Event [Line Items]
Restructuring expenses					$ 8,500,000
Subsequent Event [Member] | Minimum [Member] | January 2017 Corporate Restructuring [Member] | One-time Employee Termination Benefits [Member]
Subsequent Event [Line Items]
Restructuring expenses					$ 7,500,000
Subsequent Event [Member] | Asset Sale Agreement [Member]
Subsequent Event [Line Items]
Payment of termination fee						$ 25,000,000
Minimum percentage of consolidated assets in commercial business						50.00%
Minimum percentage of voting securities						50.00%
Subsequent Event [Member] | Settlement Agreement Cash Tender Offer [Member]
Subsequent Event [Line Items]
Tender offer expiration date		Nov. 10, 2017
Subsequent Event [Member] | Settlement Agreement Cash Tender Offer [Member] | Convertible Notes [Member]
Subsequent Event [Line Items]
Remaining aggregate principal amount		$ 25,000,000
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
Purchase of aggregate principal amount of convertible notes										$ 24,975,000
Percentage of outstanding convertible notes										99.78%
Tender offer settlement date	Nov. 14, 2017
Aggregate principal amount of outstanding debt	$ 56,000
Subsequent Event [Member] | Baxalta [Member] | License and Collaboration Agreements [Member]
Subsequent Event [Line Items]
Net milestone payments expected to be received						$ 33,000,000
Subsequent Event [Member] | Baxalta [Member] | License and Collaboration Agreements [Member] | Maximum [Member]
Subsequent Event [Line Items]
Net milestone payments expected to be received											$ 33,000,000
Subsequent Event [Member] | Ipsen [Member] | Asset Sale Agreement [Member]
Subsequent Event [Line Items]
Upfront cash payment received						$ 575,000,000					575,000,000
Subsequent Event [Member] | Ipsen [Member] | Asset Sale Agreement [Member] | Manufacturing Facility [Member]
Subsequent Event [Line Items]
Area of sublease property | ft²						68,409
Subsequent Event [Member] | Ipsen [Member] | Asset Sale Agreement [Member] | Maximum [Member]
Subsequent Event [Line Items]
Additional payments receivable on achievement of certain milestone events						$ 450,000,000					$ 450,000,000
Out-of-pocket expenses to be paid						$ 3,000,000