Aceragen (ACGN) 10-K 10 Mar 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Feb. 15, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Trading Symbol	IDRA
Entity Registrant Name	IDERA PHARMACEUTICALS, INC.
Entity Central Index Key	861,838
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		121,275,678
Entity Public Float			$ 340,140,806

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 26,586	$ 19,971
Short-term investments	33,574	21,256
Prepaid expenses and other current assets	3,082	1,203
Total current assets	63,242	42,430
Long-term investments	26,997	7,344
Property and equipment, net	1,692	1,306
Restricted cash and other assets	345	346
Total assets	92,276	51,426
Current liabilities:
Accounts payable	1,169	2,458
Accrued expenses	4,274	4,460
Current portion of note payable	261	128
Current portion of deferred revenue	1,111
Total current liabilities	6,815	7,046
Deferred revenue, net of current portion	1,262
Note payable, net of current portion	501	742
Other liabilities	116	236
Total liabilities	$ 8,694	$ 8,024
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.01 par value, Authorized - 5,000 shares:
Common stock, $0.001 par value, Authorized - 280,000 shares; Issued and outstanding -121,265 and 94,829 shares at December 31, 2015 and 2014, respectively	$ 121	$ 95
Additional paid-in capital	583,676	494,850
Accumulated deficit	(500,081)	(451,526)
Accumulated other comprehensive loss	(134)	(17)
Total stockholders' equity	83,582	43,402
Total liabilities and stockholders' equity	92,276	51,426
Series E Preferred Stock [Member]
Stockholders' equity:
Preferred stock, $0.01 par value	0	0
Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, $0.01 par value	$ 0	$ 0

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	280,000,000	280,000,000
Common stock, shares issued	121,265,000	94,829,000
Common stock, shares outstanding	121,265,000	94,829,000
Series E Preferred Stock [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares designated	0	424,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series A Preferred Stock [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares designated	1,500,000	1,500,000
Preferred stock, shares issued	1,000	1,000
Preferred stock, shares outstanding	1,000	1,000

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Alliance revenue	$ 249	$ 73	$ 47
Operating expenses:
Research and development	33,699	27,493	10,475
General and administrative	15,396	11,332	7,741
Total operating expenses	49,095	38,825	18,216
Loss from operations	(48,846)	(38,752)	(18,169)
Other income (expense):
Interest income	357	66	11
Interest expense	(105)	(27)
Foreign currency exchange gain (loss)	39	71	(68)
Net loss	(48,555)	(38,642)	(18,226)
Loss on extinguishment of convertible preferred stock and preferred stock dividends		519	2,866
Net loss applicable to common stockholders	$ (48,555)	$ (39,161)	$ (21,092)
Basic and diluted net loss per common share applicable to common stockholders (Note 12)	$ (0.42)	$ (0.47)	$ (0.48)
Shares used in computing basic and diluted net loss per common share applicable to common stockholders	115,092	82,827	43,906
Net loss	$ (48,555)	$ (38,642)	$ (18,226)
Other comprehensive loss:
Increase in unrealized loss and decrease in unrealized gain on available-for-sale securities	(117)	(10)	(7)
Other comprehensive loss	(117)	(10)	(7)
Comprehensive loss	$ (48,672)	$ (38,652)	$ (18,233)

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Conversion of Series D Preferred Stock to Common [Member]	Conversion of Series E Preferred Stock to Common [Member]	Series E Preferred Stock [Member]	Series E Preferred Stock [Member]Conversion of Series E Preferred Stock to Common [Member]	Series D Preferred Stock [Member]	Series D Preferred Stock [Member]Conversion of Series D Preferred Stock to Common [Member]	Common Stock [Member]	Common Stock [Member]Conversion of Series D Preferred Stock to Common [Member]	Common Stock [Member]Conversion of Series E Preferred Stock to Common [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Conversion of Series D Preferred Stock to Common [Member]	Additional Paid-in Capital [Member]Conversion of Series E Preferred Stock to Common [Member]	Additional Paid-in Capital [Member]Series E Preferred Stock [Member]	Additional Paid-in Capital [Member]Series D Preferred Stock [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive (Loss)/Income [Member]
Beginning balance at Dec. 31, 2012	$ 706			$ 3,701				$ 28			$ 391,635					$ (394,658)
Beginning balance, shares at Dec. 31, 2012								27,643
Shares of preferred stock outstanding, beginning Balance at Dec. 31, 2012				424
Sale of common stock and warrants, net of issuance costs	40,102							$ 31			40,071
Sale of common stock and warrants, shares								31,227
Exercise of common stock options, warrants and employee stock purchases	3,527							$ 7			3,520
Exercise of common stock options, warrants and employee stock purchases, shares								7,346
Issuance of common stock for services	26										26
Issuance of common stock for services, shares								36
Non-employee stock option expense	121										121
Stock-based compensation	1,398										1,398
Extinguishment of convertible preferred stock & recognition of warrants issued	(5,071)			$ (3,701)							(1,370)
Extinguishment of convertible preferred stock & recognition of warrants issued, shares				(424)
Recognition of convertible preferred stock	10,992			$ 5,528		$ 5,464
Recognition of convertible preferred stock, shares				424		1,124
Convertible preferred stock dividends				$ (360)		$ (756)								$ (360)	$ (756)
Unrealized loss on marketable securities	(7)																$ (7)
Net loss	(18,226)															(18,226)
Ending balance at Dec. 31, 2013	32,452			$ 5,528		$ 5,464		$ 66			434,285					(412,884)	(7)
Ending balance, shares at Dec. 31, 2013								66,252
Shares of preferred stock outstanding, Ending Balance at Dec. 31, 2013				424		1,124
Sale of common stock and warrants, net of issuance costs	37,237							$ 8			37,229
Sale of common stock and warrants, shares								7,867
Exercise of common stock options, warrants and employee stock purchases	8,456							$ 6			8,450
Exercise of common stock options, warrants and employee stock purchases, shares								5,932
Issuance of common stock for services	82										82
Issuance of common stock for services, shares								27
Non-employee stock option expense	24										24
Stock-based compensation	4,322										4,322
Convertible preferred stock dividends				$ (453)		$ (66)								$ (453)	$ (66)
Unrealized loss on marketable securities	(10)																(10)
Conversion of preferred stock to common		$ 0	$ 0	$ (5,528)	$ (5,528)	$ (5,464)	$ (5,464)		$ 6	$ 9		$ 5,458	$ 5,519
Conversion of preferred stock to common, shares					(424)		(1,124)		6,266	8,485
Net loss	(38,642)															(38,642)
Ending balance at Dec. 31, 2014	$ 43,402							$ 95			494,850					(451,526)	(17)
Ending balance, shares at Dec. 31, 2014	94,829							94,829
Shares of preferred stock outstanding, Ending Balance at Dec. 31, 2014				0
Sale of common stock and warrants, net of issuance costs	$ 80,599							$ 23			80,576
Sale of common stock and warrants, shares								23,000
Exercise of common stock options, warrants and employee stock purchases	2,546							$ 3			2,543
Exercise of common stock options, warrants and employee stock purchases, shares								3,402
Issuance of common stock for services	122										122
Issuance of common stock for services, shares								34
Non-employee stock option expense	143										143
Stock-based compensation	5,442										5,442
Unrealized loss on marketable securities	(117)																(117)
Net loss	(48,555)															(48,555)
Ending balance at Dec. 31, 2015	$ 83,582							$ 121			$ 583,676					$ (500,081)	$ (134)
Ending balance, shares at Dec. 31, 2015	121,265							121,265
Shares of preferred stock outstanding, Ending Balance at Dec. 31, 2015				0

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows from Operating Activities:
Net loss	$ (48,555)	$ (38,642)	$ (18,226)
Adjustments to reconcile net loss to net cash used in operating activities -
Loss from disposition of assets		1
Non-employee stock option expense	143	24	121
Stock-based compensation	5,442	4,322	1,398
Issuance of common stock for services rendered	122	82	26
Accretion of premiums and discounts on investments	599	213	9
Depreciation and amortization expense	488	206	137
Changes in operating assets and liabilities -
Prepaid expenses and other current assets	(1,889)	(329)	(676)
Accounts payable, accrued expenses, and other liabilities	(1,709)	2,802	74
Deferred revenue	2,373
Net cash used in operating activities	(42,986)	(31,321)	(17,137)
Cash Flows from Investing Activities:
Purchases of available-for-sale securities	(63,106)	(23,623)	(9,331)
Proceeds from maturity of available-for-sale securities	29,420	4,115
Proceeds from sale of available-for-sale securities	999
Purchases of property and equipment	(727)	(1,093)	(9)
Net cash used in investing activities	(33,414)	(20,601)	(9,340)
Cash Flows from Financing Activities:
Sale of common stock and warrants, net of issuance costs	80,599	37,137	40,202
Proceeds from issuance of note payable		825
Proceeds from exercise of common stock warrants and options and employee stock purchases	2,546	8,456	3,527
Dividends paid		(798)	(1,066)
Payments on note payable	(120)
Payments on capital lease	(10)	(5)	(4)
Net cash provided by financing activities	83,015	45,615	42,659
Net increase (decrease) in cash and cash equivalents	6,615	(6,307)	16,182
Cash and cash equivalents, beginning of year	19,971	26,278	10,096
Cash and cash equivalents, end of year	$ 26,586	$ 19,971	$ 26,278

Organization

Organization	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. Organization Idera Pharmaceuticals, Inc. (“Idera” or the “Company”) is a clinical-stage biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutics for oncology and rare diseases. The Company uses two distinct proprietary drug discovery technology platforms to design and develop drug candidates: Toll-like receptor, or TLR, targeting technology and third-generation antisense, or 3GA, technology, which the Company previously referred to as our GSO technology. The Company developed these platforms based on its scientific expertise and pioneering work with synthetic oligonucleotides as therapeutic agents. Using its TLR targeting technology, the Company designs synthetic oligonucleotide-based drug candidates to modulate the activity of specific TLRs. In addition, using its 3GA technology, the Company is developing drug candidates to turn off the messenger RNA, or mRNA, associated with disease causing genes. The Company believes that its 3GA technology may potentially reduce the immunotoxicity and increase the potency of earlier generation antisense and RNA interference, or RNAi, technologies. Idera is focused on the development of drug candidates for oncology and rare diseases characterized by small, well-defined patient populations with serious unmet medical needs. The Company plans to explore potential collaborative alliances to support late-stage development and commercialization of some of its drug candidates. The Company is developing IMO-8400 for the treatment of certain B-cell lymphomas in which the MYD88 L265P oncogenic mutation is present. Oncogenic mutations are changes in the DNA of tumor cells that promote the survival and proliferation of tumor cells. MYD88 is an adaptor protein in the TLR signaling pathway that mediates TLR signaling. The MYD88 L265P oncogenic mutation has been reported to lead to increased TLR signaling and malignant proliferation in certain B-cell lymphomas, including Waldenström’s macroglobulinemia, diffuse large B-cell lymphoma, or DLBCL, and other forms of B-cell malignancies, including Burkitt’s lymphoma, cutaneous diffuse large B-cell lymphoma (leg type), chronic lymphocytic leukemia, gastric mucosa-associated lymphoid tissue lymphoma, marginal zone lymphoma, and splenic marginal zone lymphoma. The Company’s pipeline of drug candidates includes IMO-2125 and IMO-2055, two TLR9 agonists that may have potential applications as immune therapies for the treatment of cancer. Recent advancements in cancer immunotherapy have included the approval and late-stage development of multiple checkpoint inhibitors, which are therapies that target mechanisms by which tumor cells evade detection by the immune system. Because TLR9 agonists stimulate the immune system, the Company believes that there is a scientific rationale to evaluate the combination of its TLR9 agonists with checkpoint inhibitors. In independent research in preclinical cancer models, intratumoral injection of TLR9 agonists has potentiated the anti-tumor activity of checkpoint inhibitors. The Company selected dermatomyositis as the first non-cancer rare disease for application of IMO-8400. The Company selected this indication for development based on the reported role of TLRs in the pathogenesis of the disease state, clinical feasibility, including ease of patient identification and availability of endpoints for regulatory approval and commercial potential. The Company is developing its 3GA technology to “turn off” the mRNA associated with disease causing genes. The Company designed 3GA oligonucleotides to specifically address challenges associated with earlier generation antisense and RNAi technologies. Although currently used technologies to silence RNA have demonstrated the ability to inhibit the expression of disease-associated proteins, the Company believes that to reach their full therapeutic potential, gene silencing technologies need to achieve an improved therapeutic index with efficient systemic delivery, reduced immunotoxicity and increased potency. The Company has designed its 3GA oligonucleotides to provide these attributes. At December 31, 2015, the Company had an accumulated deficit of $500,081,000. The Company expects to incur substantial operating losses in future periods. The Company does not expect to generate significant product revenue, sales-based milestones or royalties until the Company successfully completes development and obtains marketing approval for drug candidates, either alone or in collaborations with third parties, which the Company expects will take a number of years. In order to commercialize its drug candidates, the Company needs to complete clinical development and comply with comprehensive regulatory requirements. The Company is subject to a number of risks and uncertainties similar to those of other companies of the same size within the biotechnology industry, such as uncertainty of clinical trial outcomes, uncertainty of additional funding, and history of operating losses.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies (a) Basis of Presentation The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. (b) Cash, Cash Equivalents and Investments The Company considers all highly liquid investments with maturities of 90 days or less when purchased to be “cash equivalents.” Cash and cash equivalents at December 31, 2015 and 2014 consisted of cash and money market funds. Management determines the appropriate classification of marketable securities at the time of purchase. Investments that the Company does not have the positive intent to hold to maturity are classified as “available-for-sale” and reported at fair market value. Available-for-sale investments are classified as long-term if their contractual maturity is greater than one year at the balance sheet date and the Company does not have the intent to sell them in order to fund current operations. Unrealized gains and losses associated with available-for-sale investments are recorded in “Accumulated other comprehensive income” on the accompanying balance sheets. The amortization of premiums and accretion of discounts, and any realized gains and losses and declines in value judged to be other-than-temporary, and interest and dividends for all available-for-sale securities are included in “Interest income” on the accompanying statements of operations. Investments that the Company intends to hold to maturity are classified as “held-to-maturity” investments. The Company had no “held-to-maturity” investments at either December 31, 2015 or 2014. The cost of securities sold is based on the specific identification method. The Company had no realized gains or losses from available-for-sale securities in 2015, 2014 or 2013. There were no losses or other-than-temporary declines in value included in “Interest income” for any securities for the three years ended December 31, 2015. The Company had no auction rate securities as of December 31, 2015 and 2014. (c) Restricted Cash As part of the Company’s lease arrangement for its office and laboratory facility in Cambridge, Massachusetts, the Company is required to restrict cash held in a certificate of deposit securing a line of credit for the lessor. As of December 31, 2015 and 2014, the restricted cash amounted to $311,000 held in certificates of deposit securing a line of credit for the lessor. (d) Depreciation and Amortization Depreciation and amortization are computed using the straight-line method based on the estimated useful lives of the related assets. Laboratory and other equipment are depreciated over three to five years. Leasehold improvements are amortized over the remaining lease term or the related useful life, if shorter. (e) Revenue Recognition The Company recognizes revenue in accordance with the Financial Accounting Standards Board’s (FASB) Accounting Standards Codification (ASC) Topic 605, Revenue Recognition • Persuasive evidence of an arrangement exists; • delivery has occurred or services have been rendered; • the seller’s price to the buyer is fixed or determinable; and • collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria are recognized as deferred revenue in the Company’s balance sheet. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, current. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. The Company’s revenues have primarily been generated through collaborative research, development and/or commercialization agreements. The terms of these agreements typically may include payment to the Company of one or more of the following: nonrefundable, up-front license fees, research, development and commercial milestone payments, other contingent payments due based on the activities of the counterparty or the reimbursement by licensees of costs associated with patent maintenance. Each of these types of revenue are recorded as Alliance revenues in the Company’s statement of operations. For each collaborative research, development and/or commercialization agreement, which results in revenues, the Company determines (i) whether multiple deliverables exist, (ii) whether the delivered elements have value to the customer on a stand-alone basis, (iii) how the deliverables should be separated or combined and (iv) how the consideration should be allocated to the deliverables. The Company’s multiple element revenue arrangements may include the following: Up-front License Fees: Milestone Payments: Research and Development Activities: Under the terms of the GSK Agreement, the Company is eligible to receive up to approximately $100,000,000 in license, research, clinical development and commercialization milestone payments, including a $2,500,000 upfront, non-refundable, non-creditable cash payment. Approximately $9,000,000 of the milestone payments are payable by GSK upon the identification of additional targets, the completion of current and future research plans and the designation of development candidates. Approximately $89,000,000 is payable by GSK upon the achievement of clinical milestones and commercial milestones. In addition, the Company is eligible to receive royalty payments on sales upon commercialization at varying rates of up to five percent on annual net sales, as defined in the GSK Agreement. (f) Financial Instruments The fair value of the Company’s financial instruments is determined and disclosed in accordance with the three-tier fair value hierarchy specified in Note 2(m). The Company is required to disclose the estimated fair values of its financial instruments. The Company’s financial instruments consist of cash, cash equivalents, available-for-sale investments, receivables and a note payable. The estimated fair values of these financial instruments approximate their carrying values as of December 31, 2015 and 2014. As of December 31, 2015 and 2014, the Company did not have any derivatives, hedging instruments or other similar financial instruments except for the note issued under the Company’s loan and security agreement, which is discussed in Note 5(a), including put and call features which the Company determined are clearly and closely associated with the debt host and do not require bifurcation as a derivative liability, or the fair value of the feature is immaterial. (g) Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive income (loss) for the years ended December 31, 2015, 2014 and 2013 is comprised of reported net income (loss) and any change in net unrealized gains and losses on investments during each year, which is included in “Accumulated other comprehensive income” on the accompanying balance sheets. The Company applies Accounting Standards Update (“ASU”) No. 2011-05, “Comprehensive Income” by presenting the components of net income and other comprehensive income as one continuous statement. The following table includes the changes in the accumulated balance of the component of other comprehensive loss for the years ended December 31, 2015, 2014 and 2013: Year ended December 31, (In thousands) 2015 2014 2013 Accumulated unrealized loss on available-for-sale securities at beginning of period $ (17) $ (7) $ — Change during the period (117) (10) (7) Accumulated unrealized loss on available-for-sale securities at end of period $ (134) $ (17) $ (7) (h) Net Income (Loss) per Common Share applicable to Common Stockholders Basic and diluted net loss per common share applicable to common stockholders is computed using the weighted average number of shares of common stock outstanding during the period. Diluted net loss per common share applicable to common stockholders is the same as basic net loss per common share applicable to common stockholders for each of the three years in the period ended December 31, 2015 as the effects of the Company’s potential common stock equivalents are antidilutive (see Note 12). (i) Segment Reporting The Company views its operations and manages its business as one operating segment. Accordingly, the Company operates in one segment, which is the business of discovering and developing novel therapeutics that modulate immune responses through TLRs. As a result, the financial information disclosed herein represents all of the material financial information related to the Company’s principal operating segment. For all of the periods presented, all of the Company’s revenues were generated in the United States. As of December 31, 2015 and 2014, all assets were located in the United States. (j) Stock-Based Compensation The Company recognizes all share-based payments to employees and directors as expense in the statements of operations and comprehensive loss based on their fair values. The Company records compensation expense over an award’s requisite service period, or vesting period, based on the award’s fair value at the date of grant. The Company’s policy is to charge the fair value of stock options as an expense, adjusted for forfeitures, on a straight-line basis over the vesting period, which is generally four years for employees and three years for directors. The Company recorded charges of $5,442,000, $4,322,000, and $1,398,000 for the years ended December 31, 2015, 2014 and 2013, respectively, for stock-based compensation expense attributable to share-based payments made to employees and directors. The 2015 charge includes approximately $329,000 of stock-based compensation in connection with the recognition of additional expense associated with the acceleration of vesting and extension of the exercise period of a retiring director’s stock options as a result of a modification to such director’s stock options. The 2014 charge includes approximately $1,293,000 for the recognition of amortization associated with an employee’s options that were subject to accelerated vesting as a result of a modification to such employee’s stock options. The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model. The following weighted average assumptions apply to the options to purchase 3,533,750, 8,232,424, and 5,072,583 shares of common stock granted to employees and directors during the years ended December 31, 2015, 2014 and 2013, respectively: 2015 2014 2013 Average risk free interest rate 1.4 % 1.4 % 1.3 % Expected dividend yield — — — Expected lives (years) 4.2 4.4 5.0 Expected volatility 93 % 86 % 67 % Weighted average grant date fair value of options granted during the period (per share) $ 2.51 $ 2.36 $ 0.89 Weighted average exercise price of options granted during the period (per share) $ 3.74 $ 3.69 $ 1.55 The expected lives of the options and the expected volatility are based on historical experience. All options granted during the three years in the period ended December 31, 2015 were granted at exercise prices equal to the fair market value of the common stock on the dates of grant . The fair value of options that vested during 2015, 2014 and 2013 amounted to $5,403,000, $4,208,000 and $1,429,000, respectively. The intrinsic value of options exercised amounted to $761,000, $573,000 and $150,000 during 2015, 2014 and 2013, respectively. As of December 31, 2015, there was $16,163,000 of unrecognized compensation cost related to nonvested stock-based compensation arrangements, which the Company expects to recognize over a weighted average period of 3.0 years. (k) Research and Development Expenses All research and development expenses, including amounts funded by research collaborations, are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including drug development trials and studies, drug manufacturing, laboratory supplies, external research, payroll including stock-based compensation and overhead. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are accepted by the Company or the services are performed. As of December 31, 2015 and 2014, the Company recorded approximately $2,300,000 and $840,000 as prepaid research and development, respectively. (l) Concentration of Credit Risk Financial instruments that subject the Company to credit risk primarily consist of cash and cash equivalents and available-for-sale investments. The Company’s credit risk is managed by investing its cash and cash equivalents and marketable securities in highly rated money market instruments, certificates of deposit, corporate bonds, and debt securities. Due to these factors, no significant additional credit risk is believed by management to be inherent in the Company’s assets. As of December 31, 2015, all of the Company’s cash, cash equivalents and investments are held at two financial institutions. (m) Fair Value of Assets and Liabilities The Company measures fair value at the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date using assumptions that market participants would use in pricing the asset or liability (the “inputs”) into a three-tier fair value hierarchy. This fair value hierarchy gives the highest priority (Level 1) to quoted prices in active markets for identical assets or liabilities and the lowest priority (Level 3) to unobservable inputs in which little or no market data exists, requiring companies to develop their own assumptions. Observable inputs that do not meet the criteria of Level 1, and include quoted prices for similar assets or liabilities in active markets or quoted prices for identical assets and liabilities in markets that are not active, are categorized as Level 2. Level 3 inputs are those that reflect the Company’s estimates about the assumptions market participants would use in pricing the asset or liability, based on the best information available in the circumstances. Valuation techniques for assets and liabilities measured using Level 3 inputs may include unobservable inputs such as projections, estimates and management’s interpretation of current market data. These unobservable Level 3 inputs are only utilized to the extent that observable inputs are not available or cost-effective to obtain. The Company applies ASU No. 2011-04, “Fair Value Measurement (Topic 820),” in its fair value measurements and disclosures. The table below presents the assets and liabilities measured and recorded in the financial statements at fair value on a recurring basis at December 31, 2015 and 2014 categorized by the level of inputs used in the valuation of each asset and liability. (In thousands) Total Quoted Prices Significant Significant December 31, 2015 Assets Money market funds $ 26,056 $ 26,056 $ — $ — Short-term investments – commercial paper 3,974 — 3,974 — Short-term investments – corporate bonds 24,575 — 24,575 — Short-term investments – municipal bonds 5,025 — 5,025 — Long-term investments – corporate bonds 21,186 — 21,186 — Long-term investments – municipal bonds 5,811 — 5,811 — Total Assets $ 86,627 $ 26,056 $ 60,571 $ — Total Liabilities $ — $ — $ — $ — December 31, 2014 Assets Money market funds $ 17,156 $ 17,156 $ — $ — Other cash equivalents – commercial paper 2,500 — 2,500 — Short-term investments – commercial paper 4,494 — 4,494 — Short-term investments – certificate of deposit 500 — 500 — Short-term investments – corporate bonds 14,357 — 14,357 — Short-term investments – municipal bonds 1,905 — 1,905 — Long-term investments 7,344 — 7,344 — Total Assets $ 48,256 $ 17,156 $ 31,100 $ — Total Liabilities $ — $ — $ — $ — The Level 1 assets consist of money market funds, which are actively traded daily. The Level 2 assets consist of corporate bond, commercial paper, certificate of deposit and municipal bond investments whose fair value may not represent actual transactions of identical securities. The fair value of corporate and municipal bonds is generally determined from quoted market prices received from pricing services based upon quoted prices from active markets and/or other significant observable market transactions at fair value. The fair value of commercial paper is generally determined based on the relationship between the investment’s discount rate and the discount rates of the same issuer’s commercial paper available in the market which may not be actively traded daily. The fair value of certificates of deposits approximates carrying value. Since these fair values may not be based upon actual transactions of identical securities, they are classified as Level 2. Since any investments are classified as available-for-sale securities, any unrealized gains or losses are recorded in accumulated other comprehensive income or loss within stockholders’ equity on the balance sheet. The Company did not elect to measure any other financial assets or liabilities at fair value at December 31, 2015 or 2014. (n) New Accounting Pronouncements — Recently Issued In May 2014, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which was amended by ASU No. 2015-14. ASU No. 2014-09, as amended by ASU No. 2015-14, requires an entity to recognize revenue from the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In particular, this ASU addresses contracts with more than one performance obligation, as well as the accounting for some costs to obtain or fulfill a contract with a customer, and provides for additional disclosures with respect to revenues and cash flows arising from contracts with customers. This ASU will be effective for fiscal years beginning after December 15, 2017, including interim periods within that fiscal year. Early adoption of this ASU is permitted only for fiscal years beginning after December 15, 2016, including interim periods within that fiscal year. The Company is currently evaluating the effect that the adoption of this ASU will have on its financial statements. In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. ASU 2014-15 amends FASB ASC 205-40, Presentation of Financial Statements — Going Concern, by providing guidance on determining when and how reporting entities must disclose going-concern uncertainties in their financial statements, including requiring management to perform interim and annual assessments of an entity’s ability to continue as a going concern within one year of the date of issuance of the entity’s financial statements and providing certain disclosures if there is substantial doubt about the entity’s ability to continue as a going concern. ASU 2014-15 will be effective for fiscal years ending after December 15, 2016 and for interim periods thereafter. Early adoption of ASU 2014-15 is permitted. The Company is currently evaluating the effect that the adoption of ASU 2014-15 will have on its financial statements. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. The amendments in ASU 2016-01 address certain aspects of recognition, measurement, presentation and disclosure of financial instruments. ASU 2016-01 will be effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption of some of the amendments included in ASU 2016-01 to financial statements of fiscal years or interim periods that have not yet been issued is permitted as of the beginning of the fiscal year of adoption. The Company is currently evaluating the effect that the adoption of ASU 2016-01 will have on its financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases. The amendments in ASU 2016-02 will require organizations that lease assets, with lease terms of more than 12 months, to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Consistent with current Generally Accepted Accounting Principles (GAAP), the recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance or operating lease. However, unlike current GAAP which requires only capital leases to be recognized on the balance sheet, ASU No. 2016-02 will require both types of leases to be recognized on the balance sheet. ASU 2016-02 will be effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the effect that the adoption of ASU 2016-02 will have on its financial statements.

Investments

Investments	12 Months Ended
	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Investments	3. Investments The Company’s available-for-sale investments at fair value consisted of the following at December 31, 2015 and 2014: December 31, 2015 Cost Gross Gross Estimated (In thousands) Short-term investments – commercial paper $ 3,973 $ — $ 1 $ 3,974 Short-term investments – corporate bonds 24,600 (25) — 24,575 Short-term investments – municipal bonds 5,025 — — 5,025 Total short-term investments 33,598 (25) 1 33,574 Long-term investments – corporate bonds 21,289 (103) — 21,186 Long-term investments – municipal bonds 5,818 (9) 2 5,811 Total long-term investments 27,107 (112) 2 26,997 Total investments $ 60,705 $ (137) $ 3 $ 60,571 December 31, 2014 Cost Gross Gross Estimated (In thousands) Short-term investments – commercial paper $ 4,493 $ — $ 1 $ 4,494 Short-term investments – certificate of deposit 500 — — 500 Short-term investments – corporate bonds 14,364 (7) — 14,357 Short-term investments – municipal bonds 1,906 (1) — 1,905 Total short-term investments 21,263 (8) 1 21,256 Long-term investments – corporate bonds 7,354 (10) — 7,344 Total long-term investments 7,354 (10) — 7,344 Total investments $ 28,617 $ (18) $ 1 $ 28,600 The Company had no realized gains or losses from available-for-sale securities in 2015, 2014 or 2013. There were no losses or other-than-temporary declines in value included in “Interest income” for any securities for the three years ended December 31, 2015. The Company had no auction rate securities as of December 31, 2015 and 2014. See Notes 2(f) and 2(m).

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property and Equipment	4. Property and Equipment At December 31, 2015 and 2014, net property and equipment at cost consisted of the following: December 31, 2015 2014 (In thousands) Leasehold improvements $ 603 $ 525 Laboratory equipment and other 4,543 3,884 Total property and equipment, at cost 5,146 4,409 Less: Accumulated depreciation and amortization 3,454 3,103 Property and equipment, net $ 1,692 $ 1,306 Depreciation and amortization expense on property and equipment was approximately $464,000, $200,000 and $137,000 in 2015, 2014 and 2013, respectively.

Note Payable and Accrued Expens

Note Payable and Accrued Expenses	12 Months Ended
	Dec. 31, 2015
Payables and Accruals [Abstract]
Note Payable and Accrued Expenses	5. Note Payable and Accrued Expenses (a) Note Payable On September 30, 2014, the Company executed a loan and security agreement with Oxford Finance LLC (“Oxford”). Under the agreement, Oxford committed to lend the Company up to an aggregate principal amount of $3,000,000, through December 31, 2015, in one or more advances each of which is to be evidenced by a promissory note. The Company’s obligations to Oxford are secured by the specific laboratory, manufacturing, office or computer equipment financed under the agreement. Each equipment advance includes interest at a fixed interest rate equal to the greater of 7.50% per annum and 7.27% plus the three-month U.S. Libor Rate per annum, set at the time of funding. The principal amount of each equipment advance will be repaid in 36 monthly installments commencing on the applicable amortization date, which was July 1, 2015 for any equipment advance made on or before June 30, 2015. Monthly installments payable prior to July 1, 2015 consisted of interest only and monthly installments payable on or after July 1, 2015 consist of principal and accrued interest. The Company is required to pay a final payment in an amount equal to 5.7% of the aggregate advanced amount under each equipment advance at the time that the final monthly installment is due or such earlier date as specified in the loan and security agreement. The final payments will be accrued as interest expense over the term of each equipment advance using the effective interest method. The weighted average annual effective interest rate on the notes payable based on the amount advanced through December 31, 2015, including accrual of the final payment, is 11.1%. If the Company prepays all or a portion of the principal amount of any equipment advance prior to maturity, it will be required to pay Oxford a prepayment fee of between 1% and 3% of the principal amount of such equipment advance. As of December 31, 2015, the Company had received approximately $893,000 in advances under the loan and security agreement and additional advances were not available under the agreement because the draw down period had expired. Aggregate future minimum payments, reflecting payments on outstanding principal plus interest, due under the loan and security agreement as of December 31, 2015, were as follows (in thousands): Year ending December 31, 2016 $ 333 2017 333 2018 219 Total minimum payments 885 Less amount representing interest (126 ) Notes payable, gross 759 Unamortized facility fee (17 ) Accrual of final payment 20 Notes payable, balance 762 Less current portion of notes payable (261 ) Non-current portion of notes payable $ 501 The loan and security agreement includes standard affirmative and restrictive covenants, but does not include any covenants to attain or maintain any financial metrics, and also includes standard events of default, including payment defaults, breaches of covenants following any applicable cure period, a material impairment in the perfection or priority of Oxford’s security interest or in the value of the collateral, a material impairment of the prospect of repayment of the loans and a material adverse change in the business, operations or conditions of the Company. Upon the occurrence of an event of default and following any applicable cure periods, a default interest rate of an additional 5% may be applied to the outstanding loan balances, and Oxford may declare all outstanding obligations immediately due and payable and take such other actions as set forth in the loan and security agreement. The Company assessed all terms and features of the note that the Company issued under its loan and security agreement in order to identify any potential embedded features that would require bifurcation. As part of this analysis, the Company assessed the economic characteristics and risks of the note, including put and call features. The Company determined that all features of the note are clearly and closely associated with a debt host and do not require bifurcation as a derivative liability, or the fair value of the feature is immaterial. The Company will continue to reassess the features to determine if they require separate accounting on a quarterly basis. (b) Accrued Expenses At December 31, 2015 and 2014, accrued expenses consisted of the following: December 31, 2015 2014 (In thousands) Payroll and related costs $ 2,325 $ 1,453 Clinical and nonclinical trial expenses 1,339 2,068 Cost of regaining rights to cancer program — 251 Professional and consulting fees 425 530 Other 185 158 $ 4,274 $ 4,460

Collaboration and License Agree

Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration and License Agreements	6. Collaboration and License Agreements (a) Collaboration with GSK On November 20, 2015, the Company entered into a collaboration and license agreement with GSK to license, research, develop and commercialize pharmaceutical compounds from the Company’s 3GA technology for the treatment of selected targets in renal disease (the “GSK Agreement”). The initial collaboration term is currently anticipated to last between two and four years. In connection with the GSK Agreement, GSK identified an initial target for Idera to attempt to identify a potential population of development candidates to address such target under a mutually agreed upon research plan, currently estimated to take 27 months to complete. From the population of identified development candidates, GSK may designate one development candidate in its sole discretion to move forward into clinical development. Once GSK designates a development candidate, GSK would be solely responsible for the development and commercialization activities for that designated development candidate. At any time during the first two years of the GSK Agreement, GSK would have the option to select up to two additional targets, for further research under mutually agreed research plans. GSK may then designate one development candidate for each additional target, at which time GSK would have sole responsibility to develop and commercialize each such designated development candidate. In accordance with the GSK Agreement, a Joint Steering Committee (JSC) was formed with equal representation from Idera and GSK. The responsibilities of the JSC, include, but are not limited to monitoring the progress of the collaboration, reviewing research plans and dealing with disputes that may arise amongst the parties. If a dispute cannot be resolved by the JSC, GSK has final decision making authority. Under the terms of the GSK Agreement, the Company is eligible to receive up to approximately $100 million in license, research, clinical development and commercialization milestone payments, including a $2.5 million upfront, non-refundable, non-creditable cash payment. Approximately $9.0 million of the milestone payments are payable by GSK upon the identification of additional targets, the completion of current and future research plans and the designation of development candidates. Approximately $89.0 million is payable by GSK upon the achievement of clinical milestones and commercial milestones. In addition, the Company is eligible to receive royalty payments on sales upon commercialization at varying rates of up to five percent on annual net sales, as defined in the GSK Agreement. Accounting Analysis The Company evaluated the GSK Agreement in accordance with the provisions of ASC 605-25. The GSK Agreement contains the following initial deliverables: (i) a collaboration license for Idera’s proprietary technology related to the initial target (the “Collaboration License”), (ii) research services (the “Research Services”), and (iii) participation in a Joint Steering Committee (the “JSC Deliverable”). The Company has determined that the options to choose up to two additional targets and to purchase additional collaboration licenses for the Company’s proprietary technology related to each additional target are substantive options. GSK is not contractually obligated to exercise the options. Moreover, as a result of the uncertain outcome of the research activities, there is significant uncertainty as to whether GSK will decide to exercise its options for any additional targets. Consequently, the Company is at risk with regard to whether GSK will exercise the options. The Company has determined that the options to choose up to two additional targets and to purchase additional collaboration licenses for the Company’s proprietary technology related to each additional target are not priced at a significant and incremental discount. The Company has concluded that the Collaboration License does not qualify for separation from the Research Services. As it relates to the assessment of standalone value, the Company has determined that GSK cannot fully exploit the value of the Collaboration License without receipt of the Research Services from the Company. The Research Services involve unique skills and specialized expertise, particularly as it relates to the Company’s proprietary technology, which is not available in the marketplace. Accordingly, GSK must obtain the Research Services from the Company which significantly limits the ability for GSK to utilize the Collaboration License for its intended purpose on a standalone basis. Therefore, the Collaboration License does not have standalone value from the Research Services. As a result, the Collaboration License and the Research Services have been combined as a single unit of accounting (the R&D Services Unit of Accounting). The Company has concluded that the JSC Deliverable identified at the inception of the arrangement has standalone value from the other deliverables noted based on its nature. Factors considered in this determination included, among other things, the capabilities of the collaboration partner, whether any other vendor sells the item separately, whether the value of the deliverable is dependent on the other elements in the arrangement, whether there are other vendors that can provide the items and if the customer could use the item for its intended purpose without the other deliverables in the arrangement. Therefore, the Company has identified two units of accounting in connection with its initial deliverables under the GSK Agreement as follows: (i) R&D Services Unit of Accounting, and (ii) JSC Deliverable. Allocable arrangement consideration at inception of the GSK Agreement is comprised of the up-front payment of $2.5 million, which was allocated to the R&D Services Unit of Accounting. No amount was allocated to the JSC Deliverable because the related best estimate of selling price was determined to be de minimus. The $2.5 million was recorded as deferred revenue in the Company’s balance sheet and is being recognized as revenue on a straight line basis as the Research Services are delivered over the estimated 27 month research plan period. The Company has determined that certain of the payments that may be received under the GSK Agreement are related to substantive milestones. Factors considered in the evaluation of the milestones included the degree of risk associated with the achievement of the milestone, the level of effort and investment required, whether the milestone consideration was reasonable relative to the deliverables and whether the milestone was earned at least in part based on the Company’s performance. Revenues from substantive milestones, if they are nonrefundable and non-creditable, are recognized as revenue upon successful achievement of the related milestone, including the successful completion of research plans. Clinical and commercial milestones are deemed non-substantive as they are based solely on GSK’s performance. Non-substantive milestones will be recognized when achieved to the extent the Company has no remaining performance obligations under the arrangement. Payments received in connection with GSK’s identification of additional targets will be recognized as revenue as the research services are delivered under the related research plans. The Company will recognize royalty revenue in the period of sale of the related product(s), based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met. During the year ended December 31, 2015, the Company recognized revenue totaling approximately $0.1 million related to the GSK Agreement. The revenue is classified as alliance revenue in the accompanying statement of operations and comprehensive loss. As of December 31, 2015, there is approximately $2.3 million of deferred revenue related to the GSK Agreement, of which $1.1 million is classified as current portion of deferred revenue in the accompanying balance sheet. (b) Collaboration with Abbott Molecular Inc. In May 2014, the Company entered into a development and commercialization agreement with Abbott Molecular, Inc. (“Abbott Molecular”) for the development of an in vitro companion diagnostic for use in the Company’s clinical development programs to treat certain genetically defined forms of B-cell lymphoma with IMO-8400, the Company’s lead drug candidate. The agreement provides for the development and subsequent commercialization by Abbott Molecular of a companion diagnostic test utilizing polymerase chain reaction technology to identify with high sensitivity and specificity the presence in tumor biopsy samples of the oncogenic mutation referred to scientifically as MYD88 L265P. Under the agreement, Abbott Molecular is primarily responsible for developing and obtaining regulatory approvals for the companion diagnostic in accordance an agreed development plan and regulatory plan and for making the companion diagnostic test commercially available in accordance with an agreed commercialization plan. Abbott Molecular will retain all proceeds from commercialization of the companion diagnostic test. Subject to the terms of the agreement, the Company will pay Abbott Molecular fees and fund Abbott Molecular’s development of the companion diagnostic test in an approximate aggregate amount of $6.7 million over an approximately five year development period, which includes clinical trial site costs and Abbott Molecular’s costs of preparation and filing fees for regulatory submissions for the companion diagnostic with the U.S. Food and Drug Administration (“FDA”). This amount is subject to increase if Abbott Molecular incurs additional expenses in order to meet unexpected material requirements or obligations not included in the agreement or if the Company is required to conduct additional or different clinical trials which result in Abbott Molecular incurring additional costs. As of December 31, 2015, the companion diagnostic was in development and being used to screen patients in the Company’s ongoing Phase 1/2 clinical trial in patients with DLBCL harboring the MYD88 L265P oncogenic mutation. The Company incurred $0.9 million and $2.2 million in expenses under the Abbott Molecular agreement during the years ended December 31, 2015 and 2014, respectively. (c) Collaboration and License Agreement with Merck & Co. In December 2006, the Company entered into an exclusive, worldwide license and research collaboration agreement with Merck & Co. to research, develop, and commercialize vaccine products containing the Company’s TLR7, TLR8, and TLR9 agonists in the fields of cancer, infectious diseases, and Alzheimer’s disease. Under the terms of the agreement, the Company granted Merck & Co. exclusive rights to a number of the Company’s TLR7, TLR8, and TLR9 agonists for use in combination with Merck & Co.’s therapeutic and prophylactic vaccines under development in the fields of cancer, infectious diseases, and Alzheimer’s disease. There is no limit under the agreement to the number of vaccines to which Merck & Co. can apply the Company’s agonists within these fields. The Company also agreed with Merck & Co. to engage in a two-year research collaboration to generate novel agonists targeting TLR7 and TLR8 incorporating both Merck & Co. and the Company’s chemistry for use in vaccines in the defined fields. Under the terms of the agreement, Merck & Co. extended the research collaboration for two additional years to December 2010. Under the terms of the agreement, Merck & Co. agreed to pay the Company mid to upper single-digit royalties on net product sales of vaccines using the Company’s TLR agonist technology that are developed and marketed, with the royalty rates being dependent on disease indication and the TLR agonist employed. In April 2014, the Company entered into an amendment to the license and research collaboration agreement with Merck & Co. As a result of this amendment, Merck & Co.’s rights under the agreement have been limited to specified TLR7, TLR8, and TLR9 agonists that Merck & Co. selected in January 2012, and the Company regained the rights to pursue its other independently discovered TLR7, TLR8, and TLR9 agonists for use as vaccine adjuvants in the fields of cancer, infectious diseases and Alzheimer’s disease so that it now has the right to pursue its TLR7, TLR8, and TLR9 agonists for use as vaccine adjuvants in all fields. Merck & Co.’s obligations under the agreement to pay the Company milestone payments and royalties continue in effect with respect to the specified TLR7, TLR8, and TLR9 agonists. However, in connection with this amendment, the Company agreed that, to the extent that the Company licenses to third parties any TLR7, TLR8, and TLR9 agonists for use as vaccine adjuvants in the fields of cancer, infectious diseases and Alzheimer’s disease and receives income under such licenses, Merck & Co. may credit against any milestone payments and royalties it owes to the Company an amount equal to 15% of the license income received by the Company under the third-party licenses, up to a maximum of $60.0 million in credits. (d) Other License Agreements The Company has out-licensed and in-licensed therapies related to antisense technology. In 2001 Idera entered into an agreement with Ionis Pharmaceuticals, Inc. (“Ionis”), formerly Isis Pharmaceuticals, Inc., under which the Company granted Ionis a license (with the right to sublicense) to its second-generation antisense chemistry and delivery patents and patent applications, but the Company retained the right to use these patents and applications in its own drug discovery and development efforts and in collaborations with third parties.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity (a) Common Stock Pursuant to the terms of a unit purchase agreement dated as of May 5, 1998, the Company issued and sold a total of 1,199,684 shares of common stock (the “Put Shares”) at a price of $16.00 per share. Under the terms of the unit purchase agreement, the initial purchasers (the “Put Holders”) of the Put Shares have the right (the “Put Right”) to require the Company to repurchase the Put Shares. The Put Right may not be exercised by any Put Holder unless: (1) the Company liquidates, dissolves or winds up its affairs pursuant to applicable bankruptcy law, whether voluntarily or involuntarily; (2) all of the Company’s indebtedness and obligations, including without limitation the indebtedness under the Company’s then outstanding notes, has been paid in full; and (3) all rights of the holders of any series or class of capital stock ranking prior and senior to the common stock with respect to liquidation, including without limitation the Series A convertible preferred stock, have been satisfied in full. The Company may terminate the Put Right upon written notice to the Put Holders if the closing sales price of its common stock exceeds $32.00 per share for the twenty consecutive trading days prior to the date of notice of termination. Because the Put Right is not transferable, in the event that a Put Holder has transferred Put Shares since May 5, 1998, the Put Right with respect to those shares has terminated. As a consequence of the Put Right, in the event the Company is liquidated, holders of shares of common stock that do not have Put Rights with respect to such shares may receive smaller distributions per share upon the liquidation than if there were no Put Rights outstanding. As of December 31, 2015, the Company has repurchased or received documentation of the transfer of 399,950 Put Shares and 35,780 of the Put Shares continued to be held in the name of Put Holders. The Company cannot determine at this time what portion of the Put Rights of the remaining 763,954 Put Shares have terminated. As of December 31, 2015, the Company had 79,163,446 shares reserved for issuance upon the exercise of outstanding warrants and options to purchase common stock, employee and director stock purchases, conversion of Series A convertible preferred stock, and additional shares available for grant under the 2013 Stock Incentive Plan. (b) Warrants The Company has the following warrants outstanding and exercisable for the purchase of common stock at December 31, 2015: Expiration Date Shares Weighted November 4, 2016 2,810,650 $ 1.46 November 9, 2017 7,252,081 0.70 May 7, 2018 22,306,327 0.47 May 7, 2020 15,816,327 0.01 September 30, 2020 4,175,975 0.01 February 10, 2021 2,158,750 0.01 Total 54,520,110 0.36 (c) Stock Options Under the Company’s 2013 Stock Incentive Plan (the “2013 Stock Incentive Plan”), the Company may grant options to purchase common stock, stock appreciation rights, restricted stock awards and other forms of stock-based compensation. Stock options generally vest over three to four years, and expire no later than 10 years from the date of grant. A total of 15,224,460 shares of common stock, plus such additional number of shares of common stock (up to 6,946,978) as is equal to the number of shares of common stock subject to awards granted under the Company’s 2005 Stock Incentive Plan or 2008 Stock Incentive Plan which awards expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right may be issued pursuant to awards granted under the 2013 Stock Incentive Plan subject to reduction in the event that there are any “full-value awards,” as defined in the plan. The maximum number of shares of common stock with respect to which awards may be granted to any participant under the plan is 1,500,000 per calendar year. The compensation committee of the board of directors has the authority to select the employees to whom options are granted and determine the terms of each option, including (i) the number of shares of common stock subject to the option; (ii) when the option becomes exercisable, which generally may be no earlier than the first anniversary of the date of grant; (iii) the option exercise price, which must be at least 100% of the fair market value of the common stock as of the date of grant; and (iv) the duration of the option, which may not exceed 10 years. Stock options may not be re-priced without shareholder approval. Discretionary awards to non-employee directors are granted and administered by a committee comprised of independent directors. As of December 31, 2015, options to purchase a total of 8,131,950 shares of common stock were outstanding under the 2013 Stock Incentive Plan. As of December 31, 2015, 8,120,164 shares of common stock remain available for grant under the 2013 Stock Incentive Plan. The Company is no longer granting stock options or other awards pursuant to the share-based compensation plans that were utilized prior to the approval of the 2013 Stock Incentive Plan. Under these earlier plans, stock options generally vested over three to four years and expired no later than 10 years from the date of grant. As of December 31, 2015, options to purchase a total of 4,978,802 shares of common stock were outstanding under these earlier plans. During 2015 and 2014, the Company also granted as inducement grants non-statutory stock options to purchase an aggregate of 1,150,000 and 2,600,000 shares of common stock, respectively. The inducement grant awards were made outside of the 2013 Stock Incentive Plan pursuant to the NASDAQ inducement grant exception as a material component of new hires’ employment compensation. Options to purchase 3,150,000 shares as inducement grants remained outstanding at December 31, 2015. The balance of the inducement options were forfeited. The following table summarizes information related to the outstanding and exercisable options during 2015 (in thousands, except per share amounts and years): Stock Weighted-Average Weighted-Average Aggregate Outstanding at December 31, 2014 16,951 $ 3.56 Granted 3,534 3.74 Exercised (406 ) 1.44 Forfeited (2,518 ) 3.81 Expired (1,300 ) 5.65 Outstanding at December 31, 2015 16,261 3.45 7.68 $ 8,274 Exercisable at December 31, 2015 8,149 3.50 6.37 6,640 Total exercisable or expected to vest 15,563 3.45 7.62 8,134 (d) Employee Stock Purchase Plan The Company’s 1995 Employee Stock Purchase Plan (the “Stock Purchase Plan”), as amended, provides for the issuance of up to 500,000 shares of common stock to participating employees of the Company or its subsidiaries. Participation is limited to employees that would not own 5% or more of the total combined voting power or value of the stock of the Company after the grant. Under the Stock Purchase Plan, on the first day of a designated payroll deduction period, the “Offering Period,” the Company will grant to each eligible employee who has elected to participate in the Stock Purchase Plan an option to purchase shares of common stock as follows: the employee may authorize an amount, a whole percentage from 1% to 10% of such employee’s regular pay, to be deducted by the Company from such pay during the Offering Period. On the last day of the Offering Period, the employee is deemed to have exercised the option, at the option exercise price, to the extent of accumulated payroll deductions. Under the terms of the Stock Purchase Plan, the option price is an amount equal to 85% of the fair market value per share of the common stock on either the first day or the last day of the Offering Period, whichever is lower. In no event may an employee purchase in any one Offering Period a number of shares that is more than 15% of the employee’s annualized base pay divided by 85% of the market value of a share of common stock on the commencement date of the Offering Period. The compensation committee may, in its discretion, choose an Offering Period of 12 months or less for each of the Offerings and choose a different Offering Period for each Offering. Offering periods are three months in duration and commence on March 1, June 1, September 1, and December 1. In 2015, 2014, and 2013, the Company issued 27,951, 13,844, and 14,716 shares of common stock, respectively, under the Stock Purchase Plan. (e) Preferred Stock The Restated Certificate of Incorporation of the Company permits its board of directors to issue up to 5,000,000 shares of preferred stock, par value $0.01 per share, in one or more series, to designate the number of shares constituting such series, and fix by resolution, the powers, privileges, preferences and relative, optional or special rights thereof, including liquidation preferences and dividends, and conversion and redemption rights of each such series. As of December 31, 2015, the Company has designated 1,500,000 shares as Series A convertible preferred stock. (f) Series A Convertible Preferred Stock The dividends on the Series A convertible preferred stock are payable semi-annually in arrears at the rate of 1% per annum, at the election of the Company, either in cash or additional duly designated, fully paid and nonassessable shares of Series A preferred stock. The Company paid dividends in stock until 2004 when it elected to pay further dividends in cash. In the event of liquidation, dissolution or winding up of the Company, after payment of debts and other liabilities of the Company, the holders of the Series A convertible preferred stock then outstanding will be entitled to a distribution of $1 per share out of any assets available to shareholders. The Series A preferred stock is non-voting. All remaining shares of Series A preferred stock rank as to payment upon the occurrence of any liquidation event senior to the common stock. Shares of Series A preferred stock are convertible, in whole or in part, at the option of the holder into fully paid and nonassessable shares of common stock at $34.00 per share, subject to adjustment. As of December 31, 2015 and 2014, there were 655 shares of Series A convertible preferred stock outstanding. (g) Series D Convertible Preferred Stock On January 10, 2014, the Company notified Pillar Pharmaceuticals I, L.P. (“Pillar I”), an investment partnership managed by one of the Company’s directors and significant stockholders and the holder of all 1,124,260 shares of the Company’s issued and outstanding Series D redeemable convertible preferred stock (“Series D preferred stock”), of its intention to redeem the Series D preferred stock on February 10, 2014 in accordance with the terms of the Certificate of Designations, Preference and Rights of Series D Preferred Stock of the Company (the “Series D Certificate of Designations”). On February 6, 2014, Pillar I converted such shares into 6,266,175 shares of the Company’s common stock in accordance with the terms of the Series D Certificate of Designations. As a result of the conversion, no shares of the Company’s Series D preferred stock remain outstanding. On March 28, 2014, the Company filed a Certificate of Elimination of Number of Shares of Preferred Stock Designated as Series D Convertible Preferred Stock with the State of Delaware Secretary of State which eliminated the designation of the shares of Series D preferred stock. (h) Series E Convertible Preferred Stock In December 2014, the holders of all of the 424,242 shares of Series E convertible preferred stock (“Series E preferred stock”) converted such shares into 8,484,840 shares of common stock in accordance with the terms of the Certificate of Designations, Preferences and Rights of Series E Preferred Stock (the “Series E Certificate of Designations”). As a result of this conversion, no shares of Series E preferred stock remain outstanding. On March 12, 2015, the Company filed a Certificate of Elimination of Number of Shares of Preferred Stock Designated as Series E Convertible Preferred Stock with the State of Delaware Secretary of State which eliminated the designation of the shares of Series E preferred stock.

Common Stock Warrant and Option

Common Stock Warrant and Option Exercises and Employee Stock Purchases	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Common Stock Warrant and Option Exercises and Employee Stock Purchases	8. Common Stock Warrant and Option Exercises and Employee Stock Purchases The Company issued 3,402,000, 5,932,000 and 7,346,000 shares of common stock and received total proceeds of $2,546,000, $8,456,000 and $3,527,000 for warrant and stock option exercises and employee stock purchases under the Stock Purchase Plan during the years ended December 31, 2015, 2014 and 2013, respectively, as follows: 2015 2014 2013 (In thousands) Shares Proceeds Shares Proceeds Shares Proceeds Warrant exercises 2,968 $ 1,888 5,544 $ 7,534 7,160 $ 3,318 Stock option exercises 406 584 374 890 171 198 Employee stock purchases 28 74 14 32 15 11 Total 3,402 $ 2,546 5,932 $ 8,456 7,346 $ 3,527

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies (a) Lease Commitments The Company leases its facilities in Cambridge, Massachusetts and Exton, Pennsylvania. During 2015, 2014 and 2013, rent expense, including real estate taxes, was $1,744,000, $1,672,000 and $1,601,000, respectively. As part of the Cambridge facility lease, the Company is required to restrict approximately $311,000 of cash for a security deposit as of December 31, 2015. The leases are classified as operating leases. Future minimum commitments as of December 31, 2015 under the Company’s lease agreements are approximately: December 31, Operating (In thousands) 2016 $ 1,625 2017 1,174 2018 200 2019 209 2020 88 $ 3,296 The Cambridge facility lease was amended on February 21, 2014 to, among other things, extend the expiration date to August 31, 2017 subject to a three-year renewal option exercisable by the Company. The Company entered into the Exton facility lease on April 1, 2015 and amended it on September 23, 2015 to include additional space. The Exton facility lease term ends on May 31, 2020 subject to a three-year renewal option exercisable by the Company. (b) External Collaborations The Company is a party to royalty-bearing license agreements under which it has acquired rights to antisense related patents, patent applications, and technology. Each of these in-licenses automatically terminates upon the expiration of the last to expire patent included in the license. The Company has minimum payments due under one of these agreements of $10,000 in 2016. (c) Contract Obligations The Company has employment agreements with its executive officers that include future minimum commitments of approximately $3,077,000 per year. In the normal course of business, the Company enters into contracts with clinical research organizations, drug manufacturers and other vendors for preclinical and clinical research studies, research and development supplies and other services and products for operating purposes. These contracts generally provide for termination on notice, and therefore are cancellable contracts and not included in contract obligations. (d) Related-Party Transactions In November 2011, the Company issued and sold, for an aggregate purchase price of $9.5 million, 1,124,260 shares of Series D preferred stock and warrants to purchase 2,810,650 shares of its common stock with an exercise price of $1.63 per share (“Series D warrants”) pursuant to a Convertible Preferred Stock and Warrant Purchase Agreement with Pillar I, an investment partnership managed by one of the Company’s current directors and significant shareholders. The Series D warrants expire on November 4, 2016. As a result of an anti-dilution adjustment triggered by the sale of the Company’s Series E preferred stock in November, 2012, the exercise price of the Series D warrants was reduced to $1.46 per share. As discussed in Note 7(g), all shares of Series D preferred stock were converted to 6,266,175 shares of common stock in February, 2014. In November 2012, the Company issued and sold, for an aggregate purchase price of $7.0 million, 424,242 shares of Series E preferred stock and warrants to purchase 8,484,840 shares of its common stock with an exercise price of $0.70 per share (“Series E warrants”) pursuant to a Convertible Preferred Stock and Warrant Purchase Agreement with Pillar Pharmaceuticals II, L.P. (“Pillar II”), an investment partnership managed by two of the Company’s directors (one of the Company’s current directors) and one of its significant shareholders and an entity affiliated with Pillar II (together with Pillar II, the “Pillar II Entities”). The Series E warrants expire on November 9, 2017. As discussed in Note 7(h), all shares of Series E preferred stock were converted to 8,484,840 shares of common stock in December 2014. In connection with the Company’s follow-on underwritten public offering on May 7, 2013, the Company sold 5,000,000 shares of common stock and warrants to purchase 5,000,000 shares of common stock at $0.47 per share for an aggregate purchase price of $2,500,000 to Pillar Pharmaceuticals III, L.P. (“Pillar III”) and an entity affiliated with Pillar III (together with Pillar III, the “Pillar III Entities”), which is described in Note 15. In connection with the Company’s follow-on underwritten public offering on September 30, 2013, the Company sold 1,774,193 shares of common stock for an aggregate purchase price of $2,750,000 to Pillar Pharmaceuticals IV, L.P. (“Pillar IV”) and an entity affiliated with Pillar IV (together with Pillar IV, the “Pillar IV Entities”), which is described in Note 15. Youssef El Zein, a member of the Company’s board of directors, is a director and controlling stockholder of Pillar Invest Corporation (“Pillar Invest”), which is the general partner of Pillar I, Pillar II, Pillar III and Pillar IV. Mr. El Zein has voting and investment control over the securities beneficially owned by the Pillar III Entities and the Pillar IV Entities. In addition, Abdul-Wahab Umari, who was also a member of the Company’s board of directors until June 2014, is a managing partner of Pillar Invest. During 2015, the Pillar II Entities exercised 232,759 warrants to purchase common stock at a total exercise price of $163,000 and the Pillar III Entities exercised 2,600,000 warrants to purchase common stock at a total exercise price of $1,222,000. The warrant exercise prices had been established at the time that the warrants were purchased. During 2014, Pillar I exercised 1,575,758 warrants to purchase common stock at a total exercise price of $1,065,000, the Pillar II Entities exercised 1,424,242 warrants to purchase common stock at a total exercise price of $1,035,000 and the Pillar III Entities exercised 500,000 warrants to purchase common stock at a total exercise price of $235,000. The warrant exercise prices had been established at the time that the warrants were purchased. The Company issued common stock in lieu of director board and committee fees of approximately $122,000, $82,000, and $26,000 during 2015, 2014 and 2013, respectively. Such shares were issued at the market closing price on the purchase date. Additional information on related party transactions associated with the April 2013 agreements between the Company and the Pillar Entities (as defined in Note 14) is included in Note 14. See also Note 15, “Financings,” and Note 16, “Registration Rights Agreement” for additional information on related party transactions.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes The Tax Reform Act of 1986 contains provisions that limit the amount of net operating loss carryforwards (“NOLs”) and tax credit carryforwards that companies may utilize in any one year in the event of cumulative changes in ownership over a three-year period in excess of 50%. The Company has completed several financings since the effective date of the Tax Reform Act of 1986, which as of December 31, 2015, have resulted in ownership changes in excess of 50% that will significantly limit the Company’s ability to utilize its NOL and tax credit carryforwards. In December, 2014, the Company completed a study which determined that a cumulative three-year ownership change in excess of 50% had occurred in November, 2012. The 2015 and 2014 federal and state NOLs, tax credit carryforwards and related deferred tax assets shown below have been adjusted to reflect the ownership change limitations that resulted from this study. The Company has entered into additional equity transactions since November 2012 that could result in ownership changes that further limit its ability to utilize its NOL and tax credit carryforwards. The Company has not determined whether any additional ownership change limitations have resulted from equity transactions that have occurred after November 2012. As of December 31, 2015, the Company had cumulative federal and state NOLs of approximately $120,960,000 and $114,059,000 available to reduce federal and state taxable income, respectively. These NOLs expire through 2035. In addition, at December 31, 2015, the Company had cumulative federal and state tax credit carryforwards of $4,923,000 and $1,065,000, available to reduce federal and state income taxes, respectively, which expire through 2035 and 2030, respectively. The federal and state NOLs include approximately $993,000 and $654,000, respectively, of deductions related to the exercise of stock options subsequent to the adoption of ASC 718, “Stock Compensation.” These amounts represent excess tax benefits as defined under ASC 718 and have not been included in the gross deferred tax asset reflected for NOLs. As of December 31, 2015 and 2014, the components of the deferred tax assets are approximately as follows: 2015 2014 (In thousands) Operating loss carryforwards $ 46,432 $ 30,632 Tax credit carryforwards 5,627 2,174 Other 5,698 5,625 57,757 38,431 Valuation allowance (57,757 ) (38,431 ) $ — $ — The Company has provided a valuation allowance for its deferred tax asset due to the uncertainty surrounding the ability to realize this asset. The difference between the 34% U.S. federal corporate tax rate and the Company’s effective tax rate is as follows for the years ended December 31, 2015, 2014 and 2013: 2015 2014 2013 Expected federal income tax rate (34.0 )% (34.0 )% (34.0 )% Expiring credits and NOLs — — 0.2 Change in valuation allowance 39.8 (115.3 ) 43.1 Federal and state credits (7.4 ) (4.0 ) (5.0 ) State income taxes, net of federal benefit (4.5 ) (5.1 ) (5.1 ) Permanent differences 2.4 0.8 0.9 Section 382 limitation — 157.5 — Other 3.7 0.1 (0.1 ) Effective tax rate 0.0 % 0.0 % 0.0 % The Company applies ASC 740-10, “Accounting for Uncertainty in Income Taxes, an interpretation of ASC 740.” ASC 740-10 clarifies the accounting for uncertainty in income taxes recognized in financial statements and requires the impact of a tax position to be recognized in the financial statements if that position is more likely than not of being sustained by the taxing authority. The Company had no unrecognized tax benefits resulting from uncertain tax positions at December 31, 2015 and 2014. The Company has not, as of yet, conducted a study of its research and development credit carryforwards. Such a study might result in an adjustment to the Company’s research and development credit carryforwards, however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position under ASC 740-10. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the statements of operations and comprehensive loss if an adjustment was required. The Company files income tax returns in the U.S. federal and Massachusetts jurisdictions. The Company is no longer subject to tax examinations for years before 2012, except to the extent that it utilizes NOLs or tax credit carryforwards that originated before 2012. The Company does not believe there will be any material changes in its unrecognized tax positions over the next 12 months. The Company has not incurred any interest or penalties. In the event that the Company is assessed interest or penalties at some point in the future, they will be classified in the statements of operations and comprehensive loss as general and administrative expense. In November 2015, the FASB released ASU No. 2015-17, Balance Sheet Classification of Deferred Taxes. ASU No. 2015-17 requires that all deferred income tax assets, liabilities and valuation allowances applicable to the same taxing jurisdiction be presented as noncurrent in a classified statement of financial position. ASU No. 2015-17 permits early application on a prospective or retrospective basis. The Company elected to early adopt ASU No. 2015-17 on a prospective basis in its 2015 financial statements because this change in accounting principal will allow the Company to benefit from the simplified presentation of deferred income taxes. Prior period financial statements have not been retrospectively adjusted to reflect the adoption of ASU No. 2015-17.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plan	11. Employee Benefit Plan The Company has an employee benefit plan under Section 401(k) of the Internal Revenue Code. The plan allows employees to make contributions up to a specified percentage of their compensation. Under the plan, the Company matches a portion of the employees’ contributions up to a defined maximum. The Company is currently contributing up to 3% of employee base salary, by matching 50% of the first 6% of annual base salary contributed by each employee. Approximately $217,000, $139,000, and $83,000 of 401(k) benefits were charged to operating expenses during 2015, 2014 and 2013, respectively.

Net Loss per Common Share Appli

Net Loss per Common Share Applicable to Common Stockholders	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Net Loss per Common Share Applicable to Common Stockholders	12. Net Loss per Common Share Applicable to Common Stockholders For the years ended December 31, 2015 and 2014, basic and diluted net loss per common share applicable to common stockholders is computed using the weighted average number of shares of common stock outstanding during the period. Diluted net loss per common share applicable to common stockholders is the same as basic net loss per common share applicable to common stockholders as the effects of the Company’s potential common stock equivalents are antidilutive. Total antidilutive securities were 70,782,788 and 74,640,383 at December 31, 2015 and 2014, respectively, and consisted of stock options, preferred stock and warrants. For the year ended December 31, 2014, net loss per common share applicable to common stockholders reflects $66,000 and $453,000 in dividends accrued on shares of Series D preferred stock and Series E preferred stock, respectively.

Supplemental Disclosure of Cash

Supplemental Disclosure of Cash Flow Information	12 Months Ended
	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Supplemental Disclosure of Cash Flow Information	13. Supplemental Disclosure of Cash Flow Information Supplemental disclosure of cash flow information for the periods presented is as follows: Year Ended December 31, 2015 2014 2013 (In thousands) Supplemental disclosure of cash flow information: Cash paid for interest $ 93 $ 49 $ — Supplemental disclosure of non-cash financing and investing activities: Conversion of Series D preferred stock to common stock $ — $ 5,464 $ — Conversion of Series E preferred stock to common stock $ — $ 5,528 $ — Extinguishment of Series D and Series E preferred stock and issuance of related warrants $ — $ — $ 5,921 Non-cash property additions $ 123 $ 324 $ — Accrued 2013 financing transaction costs paid in 2014 $ — $ — $ 100

April 2013 Pillar Agreements

April 2013 Pillar Agreements	12 Months Ended
	Dec. 31, 2015
Text Block [Abstract]
April 2013 Pillar Agreements	14. April 2013 Pillar Agreements In April 2013, the Company entered into two agreements (the “Pillar Agreements”) with Pillar I, Pillar II and an entity affiliated with Pillar I and Pillar II (together with Pillar I and Pillar II, the “Pillar Entities”). The agreements, including the Company’s obligations to issue the warrants under the Pillar Agreements, became effective upon the consummation of the follow-on underwritten public offering of the Company’s securities on May 7, 2013. Mr. El Zein, a member of the Company’s board of directors, is a director and controlling stockholder of Pillar Invest, which is the general partner of Pillar I and Pillar II, and is a limited partner of Pillar I and Pillar II. Mr. El Zein has voting and investment control over the securities beneficially owned by the Pillar Entities. In addition, Mr. Umari, who was also a member of the Company’s board of directors until June 2014, is a managing partner of Pillar Invest. Under the first agreement entered into with Pillar I and Pillar II (the “April 22, 2013 Pillar Agreement”), Pillar I, as the sole holder of the Company’s Series D preferred stock, irrevocably waived and agreed to not exercise the rights, powers, preferences and other terms of the Series D preferred stock under Section 6 of the Series D Certificate of Designations, including without limitation the right to require the Company to purchase all or any portion of the shares of its Series D preferred stock at a price equal to the original Series D preferred stock purchase price per share plus all accrued or declared but unpaid dividends thereon upon the occurrence of specified fundamental changes such as mergers, consolidations, business combinations, stock purchases or similar transactions resulting in a person or group unaffiliated with any holder of Series D preferred stock owning 66.67% or more of the outstanding voting securities of the Company or successor entity (the “Series D Redemption Rights”). Under the April 22, 2013 Pillar Agreement, the Company agreed to seek approval and each of Pillar I and Pillar II agreed to vote in favor, of the following proposals at the Company’s 2013 annual meeting of stockholders held on July 26, 2013 (“Annual Meeting”): • amendments to the Series D Certificate of Designations for the Series D preferred stock to: • modify the dividend provisions of the Series D Certificate of Designations to change the date after which the Company may elect to pay dividends in shares of its common stock from December 31, 2014 to October 1, 2013, and to allow for the payment of such dividends in shares of a to-be-created new series of non-voting preferred stock in the event that payment of such dividends may not be made in shares of its common stock as a result of the application of the beneficial ownership and voting power limitations set forth the Series D Certificate of Designations; and • modify the Series D Certificate of Designations to provide, in the event of a sale of the Company, for the distribution of any assets that remain available for distribution to its stockholders, after payment to the holders of its Series A convertible preferred stock and any other class of its capital stock that ranks senior to its Series D preferred stock, to the holders of the Company’s Series D preferred stock on a pro rata basis with the holders of its common stock, Series E preferred stock and such new series of non-voting preferred stock; and • amendments to the Series E Certificate of Designations to: • modify the dividend provisions of the Series E Certificate of Designations to allow for the payment of dividends in shares of its common stock commencing October 1, 2013; and • allow for the payment of dividends in shares of a to-be-created new series of non-voting preferred stock in the event that payment of such dividends may not be made in shares of its common stock as a result of the application of the beneficial ownership and voting power limitations set forth in the Series E Certificate of Designations. Under the second agreement with the Pillar Entities (the “April 30, 2013 Pillar Agreement”), Pillar I irrevocably waived the right of the holders of the Series D preferred stock under Section 2.1 of the Series D Certificate of Designations to receive, in the event of a voluntary or involuntary liquidation, dissolution or winding up of the Company (a “Liquidation”), an amount per share of Series D preferred stock equal to the original issue price of such share of Series D preferred stock plus any dividends accrued or declared but unpaid thereon to the extent such amount is greater than the amount that would have been payable with respect to such share had all shares of Series D preferred stock been converted into shares of the Company’s common stock immediately prior to such Liquidation, and that upon a Liquidation the holders of the Series D preferred stock will receive an amount per share of Series D preferred stock equal to the amount that would be payable with respect to such share had all shares of Series D preferred stock been converted into shares of common stock immediately prior to such Liquidation. In addition, under the April 30, 2013 Pillar Agreement, Pillar II and the entity affiliated with Pillar I and Pillar II, as the holders of 100% of the Company’s Series E preferred stock, irrevocably waived the right of the holders of the Series E preferred stock under Section 2.1.1 of the Series E Certificate of Designations to receive, in the event of a Liquidation, an amount per share of Series E preferred stock equal to the original issue price of such share of Series E preferred stock plus any dividends accrued or declared but unpaid thereon to the extent such amount is greater than the amount that would have been payable with respect to such share had all shares of Series E preferred stock been converted into shares of common stock immediately prior to such Liquidation, and that upon a Liquidation the holders of the Series E preferred stock will receive under Section 2.1 of the Series E Certificate of Designations an amount per share of Series E preferred stock equal to the amount that would be payable with respect to such share had all shares of Series E preferred stock been converted into shares of common stock immediately prior to such Liquidation. In accordance with the terms of the Pillar Agreements, the Company sought approval from its stockholders of amendments to the Series D Certificate of Designations and Series E Certificate of Designations to effect the changes described above to the dividend and liquidation provisions of the Company’s Series D preferred stock and Series E preferred stock, the redemption rights of the holders of its Series D preferred stock and the rights of the holders of its Series D preferred stock to distributions in the event of a sale of the Company. These matters were approved at the 2013 Annual Meeting. Under the April 22, 2013 Pillar Agreement, in consideration of the agreements of Pillar I and II under the April 22, 2013 Pillar Agreement and the delivery of the waiver by Pillar I, and for no additional cash consideration, the Company issued to Pillar I warrants, the “Pillar I Warrants,” to purchase up to 1,000,000 shares of the Company’s common stock at an exercise price of $0.61 per share. In addition, under the April 30, 2013 Pillar Agreement, in consideration of the agreements of the Pillar Entities under the April 30, 2013 Pillar Agreement and the delivery of the waivers by the Pillar Entities, and for no additional cash consideration, the Company issued to the Pillar Entities warrants (the “Additional Pillar Warrants,” and together with the Pillar I Warrants, the “Pillar Warrants”), to purchase up to an aggregate of 1,000,000 shares of the Company’s common stock at an exercise price of $0.79 per share. The Pillar Warrants became exercisable immediately upon issuance. The Pillar I Warrants will expire if not exercised on or prior to the fifth anniversary from the date of issuance and the Additional Pillar Warrants will expire if not exercised on or prior to June 1, 2014. The Pillar I Warrants provide that, after the second anniversary of the date of issuance, the Company may redeem such Pillar I Warrants for $0.01 per share of common stock issuable on exercise of such Pillar I Warrants following notice to the holder thereof if the closing price of its common stock for 20 or more trading days in a period of 30 consecutive trading days is greater than or equal to $2.80 per share. In connection with the Pillar Agreements, the Company filed a registration statement that became effective on July 10, 2013, registering the resale of the shares of common stock issuable upon exercise of the Pillar Warrants. All of the Pillar I Warrants and the Additional Pillar Warrants were exercised during 2014. The amendments to the Series D Certificate of Designations and Series E Certificate of Designations did not become effective until the amendments were approved by the Company’s stockholders at the 2013 Annual Meeting. As discussed in Note 7(g), all shares of Series D preferred stock were converted to common stock in February, 2014. As discussed in Note 7(h), all shares of Series E preferred stock were converted to common stock in December 2014. Since Pillar I irrevocably waived and agreed to not exercise the Series D Redemption Rights, the Company reassessed its accounting in May 2013 for the Series D preferred stock, which had been classified as temporary equity in the Company’s condensed balance sheet because the Series D Redemption Rights represented a contingent put feature that was outside the Company’s control. Upon effectiveness of this waiver, the contingent put feature ceased to exist. In addition, the Pillar Entities irrevocably waived the liquidation preferences of both the Series D preferred stock and the Series E preferred stock. The Company concluded that these irrevocable waivers of the Series D Redemption Rights and the Series D and Series E liquidation preferences, which became effective on May 7, 2013, represented changes to the fundamental terms of both the Series D preferred stock and the Series E preferred stock. As a result, the Company has accounted for these irrevocable waivers as an extinguishment of the Series D preferred stock and the Series E preferred stock and changed the classification of the Series D preferred stock from temporary equity to permanent equity. The Company compared (1) the sum of the fair values of the Series D preferred stock, the Series E preferred stock and the Pillar Warrants immediately after the effectiveness of the waivers to (2) the sum of the carrying values of the Series D preferred stock and Series E preferred stock immediately prior to the effectiveness of the waivers on May 7, 2013. The Company recorded the excess of the aggregate fair value of the preferred stock plus the Pillar Warrants immediately after the effectiveness of the waivers over the aggregate carrying value of the preferred stock immediately prior to May 7, 2013 as a loss on extinguishment and classified the fair values, immediately after the effectiveness of the waivers, of the Series D preferred stock, the Series E preferred stock and the Pillar Warrants within permanent equity on its balance sheet. The effect of this extinguishment accounting on the Company’s financial statements was to (1) remove the $5,921,000 carrying value of the Series D preferred stock immediately prior to the extinguishment from temporary equity; (2) record the $5,464,000 fair value of the Series D preferred stock immediately after the extinguishment in permanent equity (“equity”); (3) remove the $3,701,000 carrying value of the Series E preferred stock immediately prior to the extinguishment from equity; (4) record the $5,528,000 fair value of the Series E preferred stock immediately after the extinguishment in equity; (5) record the $380,000 fair value of the Pillar Warrants in equity; and (6) record a $1,750,000 extinguishment loss to net loss applicable to common stockholders. These accounting entries resulted in a $5,921,000 net increase in stockholders’ equity on its balance sheet. The Company determined the fair value of the Series D preferred stock and the Series E preferred stock as of May 7, 2013, the date the above described waivers became effective, based on the Option Pricing Method (“OPM”) which is a market based approach to imply the aggregate equity value of the Company by using the closing price of the Company’s publicly traded common stock as of the May 7, 2013 valuation date. Under the OPM, the fair value of preferred stock and common stock are determined based on the net value of a series of call options representing the present value of the expected future returns to each shareholder class. Essentially, the rights of the common stock are equivalent to a call option on any value of the Company above any cumulative preferred stock liquidation preference. The analysis involves calculating the equity value breakeven points at which the various equity classes would participate, or convert in the case of preferred stock, or exercise in the case of stock options and warrants. The Company used the Black-Scholes option pricing model to compute the fair value of the Pillar Warrants as of the May 7, 2013 effective date on which the Pillar Warrants were issued based on the following assumptions and other inputs: Pillar I Additional Common stock price $ 0.57 $ 0.57 Warrant exercise price $ 0.61 $ 0.79 Term of warrant (years) 5.0 1.1 Expected volatility 62 % 67 % Average risk free interest rate 0.8 % 0.1 % Expected dividend yield — — Expected percentage of warrants to be exercised 100 % 100 % The closing price of the Company’s common stock is readily determinable since it is publicly traded. The warrant exercise prices and the warrant terms are readily determinable from the warrant agreements. The expected volatility is based on the actual stock-price volatility over a period equal to the greater of the term of the warrant or three years. The assumed risk-free interest rate is based on the U.S. Treasury security rate with a term equal to the term of the warrant. The assumed dividend yield of zero is based on the fact that the Company has never paid cash dividends to common stockholders and has no present intention to pay cash dividends to common stockholders. The Company assumed that future financings would dilute the warrant holder’s ownership in the Company such that the 19.99% ownership limitation would not prevent the warrant holder from exercising all of the warrants during the term of the warrants.

Financings

Financings	12 Months Ended
	Dec. 31, 2015
Disclosure Text Block Supplement [Abstract]
Financings	15. Financings February 19, 2015 Follow-on Underwritten Public Offering On February 19, 2015, the Company closed a follow-on underwritten public offering, in which it sold 23,000,000 shares of common stock at a price to the public of $3.75 per share for aggregate gross proceeds of $86.3 million. The net proceeds to the Company from the offering, after deducting underwriters’ discounts and commissions and other offering costs and expenses, were $80.6 million. Investment funds affiliated with Baker Bros. Advisors LP and two members of the Company’s board of directors purchased 5,333,333 shares in this offering at the $3.75 per share purchase price. On February 19, 2015, Baker Bros. Advisors LP and certain of its affiliated funds (collectively, “Baker Brothers”) held 6,965,432 shares of the Company’s common stock, warrants to purchase up to 20,316,327 shares of the Company’s common stock at an exercise price of $0.47 per share and pre-funded warrants to purchase up to 22,151,052 shares of the Company’s common stock at an exercise price of $0.01 per share. February 10, 2014 Follow-on Underwritten Public Offering On February 10, 2014, the Company closed a follow-on underwritten public offering, in which it sold 7,867,438 shares of common stock at a price to the public of $4.00 per share and pre-funded warrants to purchase up to 2,158,750 shares of common stock at a price to the public of $3.99 per share for aggregate gross proceeds of $40.1 million. The pre-funded warrants have an exercise price of $0.01 per share and will expire if not exercised by February 10, 2021. The net proceeds to the Company from the offering, after deducting underwriters’ discounts and commissions and other offering costs and expenses and excluding the proceeds of the exercise of the warrants, if any, were approximately $37.2 million. September 30, 2013 Follow-on Underwritten Public Offering On September 30, 2013, the Company closed a follow-on underwritten public offering, in which it sold 13,727,251 shares of common stock at a price to the public of $1.55 per share and pre-funded warrants to purchase up to 4,175,975 shares of common stock at a price to the public of $1.54 per share for aggregate gross proceeds of $27.7 million. The pre-funded warrants have an exercise price of $0.01 per share and will expire if not exercised by September 30, 2020. The net proceeds to the Company from the offering, after deducting underwriters’ discounts and commissions and offering costs and expenses and excluding the proceeds of the exercise of the warrants, if any, were approximately $25.7 million. May 7, 2013 Follow-on Underwritten Public Offering On May 7, 2013, the Company closed a follow-on underwritten public offering, in which it sold 17,500,000 shares of common stock, together with matching warrants to purchase up to 17,500,000 shares of common stock, and pre-funded warrants to purchase up to 15,816,327 shares of common stock, together with matching warrants to purchase up to 15,816,327 shares of common stock, for aggregate gross proceeds of $16.5 million as follows: Combined Common Pre-funded Matching Common stock and matching warrants sold (shares) $ 0.50 17,500,000 — 17,500,000 Pre-funded warrants and matching warrants sold (shares) $ 0.49 — 15,816,327 15,816,327 Total (shares) 17,500,000 15,816,327 33,316,327 Warrant exercise price (per share) — — $ 0.01 $ 0.47 Term of warrant (years) — — 7.0 5.0 The net proceeds to the Company from the offering, after deducting underwriters’ discounts and commissions and offering costs and expenses and excluding the proceeds of the exercise of the warrants, if any, were approximately $14.5 million. The warrants and the pre-funded warrants each provide that, after the second anniversary of the date of issuance, the Company may redeem the warrants for $0.01 per share of common stock issuable on exercise of the warrants following 30 days’ prior written notice to the holder if the closing price of the common stock for 20 or more trading days in a period of 30 consecutive trading days is greater than or equal to $2.80.

Registration Rights Agreement

Registration Rights Agreement	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Registration Rights Agreement	16. Registration Rights Agreement On February 9, 2015, the Company entered into a registration rights agreement with investment funds (the “Selling Stockholders”) affiliated with Baker Bros. Advisors LP and two members of the Company’s board of directors, relating to the registration for resale of the shares of the Company’s common stock held by the Selling Stockholders, including the shares of the Company’s common stock that may be issued upon the exercise of warrants held by the Selling Stockholders (collectively, the “Registrable Shares”). Under the registration rights agreement, the Company has agreed to file a registration statement on Form S-3

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2015
Subsequent Events [Abstract]
Subsequent Event	17. Subsequent Event The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure.

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation	(a) Basis of Presentation The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Cash, Cash Equivalents and Investments	(b) Cash, Cash Equivalents and Investments The Company considers all highly liquid investments with maturities of 90 days or less when purchased to be “cash equivalents.” Cash and cash equivalents at December 31, 2015 and 2014 consisted of cash and money market funds. Management determines the appropriate classification of marketable securities at the time of purchase. Investments that the Company does not have the positive intent to hold to maturity are classified as “available-for-sale” and reported at fair market value. Available-for-sale investments are classified as long-term if their contractual maturity is greater than one year at the balance sheet date and the Company does not have the intent to sell them in order to fund current operations. Unrealized gains and losses associated with available-for-sale investments are recorded in “Accumulated other comprehensive income” on the accompanying balance sheets. The amortization of premiums and accretion of discounts, and any realized gains and losses and declines in value judged to be other-than-temporary, and interest and dividends for all available-for-sale securities are included in “Interest income” on the accompanying statements of operations. Investments that the Company intends to hold to maturity are classified as “held-to-maturity” investments. The Company had no “held-to-maturity” investments at either December 31, 2015 or 2014. The cost of securities sold is based on the specific identification method. The Company had no realized gains or losses from available-for-sale securities in 2015, 2014 or 2013. There were no losses or other-than-temporary declines in value included in “Interest income” for any securities for the three years ended December 31, 2015. The Company had no auction rate securities as of December 31, 2015 and 2014.
Restricted Cash	(c) Restricted Cash As part of the Company’s lease arrangement for its office and laboratory facility in Cambridge, Massachusetts, the Company is required to restrict cash held in a certificate of deposit securing a line of credit for the lessor. As of December 31, 2015 and 2014, the restricted cash amounted to $311,000 held in certificates of deposit securing a line of credit for the lessor.
Depreciation and Amortization	(d) Depreciation and Amortization Depreciation and amortization are computed using the straight-line method based on the estimated useful lives of the related assets. Laboratory and other equipment are depreciated over three to five years. Leasehold improvements are amortized over the remaining lease term or the related useful life, if shorter.
Revenue Recognition	(e) Revenue Recognition The Company recognizes revenue in accordance with the Financial Accounting Standards Board’s (FASB) Accounting Standards Codification (ASC) Topic 605, Revenue Recognition • Persuasive evidence of an arrangement exists; • delivery has occurred or services have been rendered; • the seller’s price to the buyer is fixed or determinable; and • collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria are recognized as deferred revenue in the Company’s balance sheet. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, current. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. The Company’s revenues have primarily been generated through collaborative research, development and/or commercialization agreements. The terms of these agreements typically may include payment to the Company of one or more of the following: nonrefundable, up-front license fees, research, development and commercial milestone payments, other contingent payments due based on the activities of the counterparty or the reimbursement by licensees of costs associated with patent maintenance. Each of these types of revenue are recorded as Alliance revenues in the Company’s statement of operations. For each collaborative research, development and/or commercialization agreement, which results in revenues, the Company determines (i) whether multiple deliverables exist, (ii) whether the delivered elements have value to the customer on a stand-alone basis, (iii) how the deliverables should be separated or combined and (iv) how the consideration should be allocated to the deliverables. The Company’s multiple element revenue arrangements may include the following: Up-front License Fees: Milestone Payments: Research and Development Activities: Under the terms of the GSK Agreement, the Company is eligible to receive up to approximately $100,000,000 in license, research, clinical development and commercialization milestone payments, including a $2,500,000 upfront, non-refundable, non-creditable cash payment. Approximately $9,000,000 of the milestone payments are payable by GSK upon the identification of additional targets, the completion of current and future research plans and the designation of development candidates. Approximately $89,000,000 is payable by GSK upon the achievement of clinical milestones and commercial milestones. In addition, the Company is eligible to receive royalty payments on sales upon commercialization at varying rates of up to five percent on annual net sales, as defined in the GSK Agreement.
Financial Instruments	(f) Financial Instruments The fair value of the Company’s financial instruments is determined and disclosed in accordance with the three-tier fair value hierarchy specified in Note 2(m). The Company is required to disclose the estimated fair values of its financial instruments. The Company’s financial instruments consist of cash, cash equivalents, available-for-sale investments, receivables and a note payable. The estimated fair values of these financial instruments approximate their carrying values as of December 31, 2015 and 2014. As of December 31, 2015 and 2014, the Company did not have any derivatives, hedging instruments or other similar financial instruments except for the note issued under the Company’s loan and security agreement, which is discussed in Note 5(a), including put and call features which the Company determined are clearly and closely associated with the debt host and do not require bifurcation as a derivative liability, or the fair value of the feature is immaterial.
Comprehensive Income (Loss)	(g) Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive income (loss) for the years ended December 31, 2015, 2014 and 2013 is comprised of reported net income (loss) and any change in net unrealized gains and losses on investments during each year, which is included in “Accumulated other comprehensive income” on the accompanying balance sheets. The Company applies Accounting Standards Update (“ASU”) No. 2011-05, “Comprehensive Income” by presenting the components of net income and other comprehensive income as one continuous statement. The following table includes the changes in the accumulated balance of the component of other comprehensive loss for the years ended December 31, 2015, 2014 and 2013: Year ended December 31, (In thousands) 2015 2014 2013 Accumulated unrealized loss on available-for-sale securities at beginning of period $ (17) $ (7) $ — Change during the period (117) (10) (7) Accumulated unrealized loss on available-for-sale securities at end of period $ (134) $ (17) $ (7)
Net Income (Loss) per Common Share Applicable to Common Stockholders	(h) Net Income (Loss) per Common Share applicable to Common Stockholders Basic and diluted net loss per common share applicable to common stockholders is computed using the weighted average number of shares of common stock outstanding during the period. Diluted net loss per common share applicable to common stockholders is the same as basic net loss per common share applicable to common stockholders for each of the three years in the period ended December 31, 2015 as the effects of the Company’s potential common stock equivalents are antidilutive (see Note 12).
Segment Reporting	(i) Segment Reporting The Company views its operations and manages its business as one operating segment. Accordingly, the Company operates in one segment, which is the business of discovering and developing novel therapeutics that modulate immune responses through TLRs. As a result, the financial information disclosed herein represents all of the material financial information related to the Company’s principal operating segment. For all of the periods presented, all of the Company’s revenues were generated in the United States. As of December 31, 2015 and 2014, all assets were located in the United States.
Stock-Based Compensation	(j) Stock-Based Compensation The Company recognizes all share-based payments to employees and directors as expense in the statements of operations and comprehensive loss based on their fair values. The Company records compensation expense over an award’s requisite service period, or vesting period, based on the award’s fair value at the date of grant. The Company’s policy is to charge the fair value of stock options as an expense, adjusted for forfeitures, on a straight-line basis over the vesting period, which is generally four years for employees and three years for directors. The Company recorded charges of $5,442,000, $4,322,000, and $1,398,000 for the years ended December 31, 2015, 2014 and 2013, respectively, for stock-based compensation expense attributable to share-based payments made to employees and directors. The 2015 charge includes approximately $329,000 of stock-based compensation in connection with the recognition of additional expense associated with the acceleration of vesting and extension of the exercise period of a retiring director’s stock options as a result of a modification to such director’s stock options. The 2014 charge includes approximately $1,293,000 for the recognition of amortization associated with an employee’s options that were subject to accelerated vesting as a result of a modification to such employee’s stock options. The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model. The following weighted average assumptions apply to the options to purchase 3,533,750, 8,232,424, and 5,072,583 shares of common stock granted to employees and directors during the years ended December 31, 2015, 2014 and 2013, respectively: 2015 2014 2013 Average risk free interest rate 1.4 % 1.4 % 1.3 % Expected dividend yield — — — Expected lives (years) 4.2 4.4 5.0 Expected volatility 93 % 86 % 67 % Weighted average grant date fair value of options granted during the period (per share) $ 2.51 $ 2.36 $ 0.89 Weighted average exercise price of options granted during the period (per share) $ 3.74 $ 3.69 $ 1.55 The expected lives of the options and the expected volatility are based on historical experience. All options granted during the three years in the period ended December 31, 2015 were granted at exercise prices equal to the fair market value of the common stock on the dates of grant . The fair value of options that vested during 2015, 2014 and 2013 amounted to $5,403,000, $4,208,000 and $1,429,000, respectively. The intrinsic value of options exercised amounted to $761,000, $573,000 and $150,000 during 2015, 2014 and 2013, respectively. As of December 31, 2015, there was $16,163,000 of unrecognized compensation cost related to nonvested stock-based compensation arrangements, which the Company expects to recognize over a weighted average period of 3.0 years.
Research and Development Expenses	(k) Research and Development Expenses All research and development expenses, including amounts funded by research collaborations, are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including drug development trials and studies, drug manufacturing, laboratory supplies, external research, payroll including stock-based compensation and overhead. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are accepted by the Company or the services are performed. As of December 31, 2015 and 2014, the Company recorded approximately $2,300,000 and $840,000 as prepaid research and development, respectively.
Concentration of Credit Risk	(l) Concentration of Credit Risk Financial instruments that subject the Company to credit risk primarily consist of cash and cash equivalents and available-for-sale investments. The Company’s credit risk is managed by investing its cash and cash equivalents and marketable securities in highly rated money market instruments, certificates of deposit, corporate bonds, and debt securities. Due to these factors, no significant additional credit risk is believed by management to be inherent in the Company’s assets. As of December 31, 2015, all of the Company’s cash, cash equivalents and investments are held at two financial institutions.
Fair Value of Assets and Liabilities	(m) Fair Value of Assets and Liabilities The Company measures fair value at the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date using assumptions that market participants would use in pricing the asset or liability (the “inputs”) into a three-tier fair value hierarchy. This fair value hierarchy gives the highest priority (Level 1) to quoted prices in active markets for identical assets or liabilities and the lowest priority (Level 3) to unobservable inputs in which little or no market data exists, requiring companies to develop their own assumptions. Observable inputs that do not meet the criteria of Level 1, and include quoted prices for similar assets or liabilities in active markets or quoted prices for identical assets and liabilities in markets that are not active, are categorized as Level 2. Level 3 inputs are those that reflect the Company’s estimates about the assumptions market participants would use in pricing the asset or liability, based on the best information available in the circumstances. Valuation techniques for assets and liabilities measured using Level 3 inputs may include unobservable inputs such as projections, estimates and management’s interpretation of current market data. These unobservable Level 3 inputs are only utilized to the extent that observable inputs are not available or cost-effective to obtain. The Company applies ASU No. 2011-04, “Fair Value Measurement (Topic 820),” in its fair value measurements and disclosures. The table below presents the assets and liabilities measured and recorded in the financial statements at fair value on a recurring basis at December 31, 2015 and 2014 categorized by the level of inputs used in the valuation of each asset and liability. (In thousands) Total Quoted Prices Significant Significant December 31, 2015 Assets Money market funds $ 26,056 $ 26,056 $ — $ — Short-term investments – commercial paper 3,974 — 3,974 — Short-term investments – corporate bonds 24,575 — 24,575 — Short-term investments – municipal bonds 5,025 — 5,025 — Long-term investments – corporate bonds 21,186 — 21,186 — Long-term investments – municipal bonds 5,811 — 5,811 — Total Assets $ 86,627 $ 26,056 $ 60,571 $ — Total Liabilities $ — $ — $ — $ — December 31, 2014 Assets Money market funds $ 17,156 $ 17,156 $ — $ — Other cash equivalents – commercial paper 2,500 — 2,500 — Short-term investments – commercial paper 4,494 — 4,494 — Short-term investments – certificate of deposit 500 — 500 — Short-term investments – corporate bonds 14,357 — 14,357 — Short-term investments – municipal bonds 1,905 — 1,905 — Long-term investments 7,344 — 7,344 — Total Assets $ 48,256 $ 17,156 $ 31,100 $ — Total Liabilities $ — $ — $ — $ — The Level 1 assets consist of money market funds, which are actively traded daily. The Level 2 assets consist of corporate bond, commercial paper, certificate of deposit and municipal bond investments whose fair value may not represent actual transactions of identical securities. The fair value of corporate and municipal bonds is generally determined from quoted market prices received from pricing services based upon quoted prices from active markets and/or other significant observable market transactions at fair value. The fair value of commercial paper is generally determined based on the relationship between the investment’s discount rate and the discount rates of the same issuer’s commercial paper available in the market which may not be actively traded daily. The fair value of certificates of deposits approximates carrying value. Since these fair values may not be based upon actual transactions of identical securities, they are classified as Level 2. Since any investments are classified as available-for-sale securities, any unrealized gains or losses are recorded in accumulated other comprehensive income or loss within stockholders’ equity on the balance sheet. The Company did not elect to measure any other financial assets or liabilities at fair value at December 31, 2015 or 2014.
New Accounting Pronouncements - Recently Issued	(n) New Accounting Pronouncements — Recently Issued In May 2014, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which was amended by ASU No. 2015-14. ASU No. 2014-09, as amended by ASU No. 2015-14, requires an entity to recognize revenue from the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In particular, this ASU addresses contracts with more than one performance obligation, as well as the accounting for some costs to obtain or fulfill a contract with a customer, and provides for additional disclosures with respect to revenues and cash flows arising from contracts with customers. This ASU will be effective for fiscal years beginning after December 15, 2017, including interim periods within that fiscal year. Early adoption of this ASU is permitted only for fiscal years beginning after December 15, 2016, including interim periods within that fiscal year. The Company is currently evaluating the effect that the adoption of this ASU will have on its financial statements. In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. ASU 2014-15 amends FASB ASC 205-40, Presentation of Financial Statements — Going Concern, by providing guidance on determining when and how reporting entities must disclose going-concern uncertainties in their financial statements, including requiring management to perform interim and annual assessments of an entity’s ability to continue as a going concern within one year of the date of issuance of the entity’s financial statements and providing certain disclosures if there is substantial doubt about the entity’s ability to continue as a going concern. ASU 2014-15 will be effective for fiscal years ending after December 15, 2016 and for interim periods thereafter. Early adoption of ASU 2014-15 is permitted. The Company is currently evaluating the effect that the adoption of ASU 2014-15 will have on its financial statements. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. The amendments in ASU 2016-01 address certain aspects of recognition, measurement, presentation and disclosure of financial instruments. ASU 2016-01 will be effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption of some of the amendments included in ASU 2016-01 to financial statements of fiscal years or interim periods that have not yet been issued is permitted as of the beginning of the fiscal year of adoption. The Company is currently evaluating the effect that the adoption of ASU 2016-01 will have on its financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases. The amendments in ASU 2016-02 will require organizations that lease assets, with lease terms of more than 12 months, to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Consistent with current Generally Accepted Accounting Principles (GAAP), the recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance or operating lease. However, unlike current GAAP which requires only capital leases to be recognized on the balance sheet, ASU No. 2016-02 will require both types of leases to be recognized on the balance sheet. ASU 2016-02 will be effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the effect that the adoption of ASU 2016-02 will have on its financial statements.
Accounting for Uncertainty in Income Taxes	The Company applies ASC 740-10, “Accounting for Uncertainty in Income Taxes, an interpretation of ASC 740.” ASC 740-10 clarifies the accounting for uncertainty in income taxes recognized in financial statements and requires the impact of a tax position to be recognized in the financial statements if that position is more likely than not of being sustained by the taxing authority. The Company had no unrecognized tax benefits resulting from uncertain tax positions at December 31, 2015 and 2014.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Change in Accumulated Balance of the Component of Other Comprehensive Loss	The following table includes the changes in the accumulated balance of the component of other comprehensive loss for the years ended December 31, 2015, 2014 and 2013: Year ended December 31, (In thousands) 2015 2014 2013 Accumulated unrealized loss on available-for-sale securities at beginning of period $ (17) $ (7) $ — Change during the period (117) (10) (7) Accumulated unrealized loss on available-for-sale securities at end of period $ (134) $ (17) $ (7)
Schedule of Assumptions Used to Determine Fair Value of Stock Options Granted During Period	The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model. The following weighted average assumptions apply to the options to purchase 3,533,750, 8,232,424, and 5,072,583 shares of common stock granted to employees and directors during the years ended December 31, 2015, 2014 and 2013, respectively: 2015 2014 2013 Average risk free interest rate 1.4 % 1.4 % 1.3 % Expected dividend yield — — — Expected lives (years) 4.2 4.4 5.0 Expected volatility 93 % 86 % 67 % Weighted average grant date fair value of options granted during the period (per share) $ 2.51 $ 2.36 $ 0.89 Weighted average exercise price of options granted during the period (per share) $ 3.74 $ 3.69 $ 1.55
Assets and Liabilities Measured at Fair Value on a Recurring Basis	The table below presents the assets and liabilities measured and recorded in the financial statements at fair value on a recurring basis at December 31, 2015 and 2014 categorized by the level of inputs used in the valuation of each asset and liability. (In thousands) Total Quoted Prices Significant Significant December 31, 2015 Assets Money market funds $ 26,056 $ 26,056 $ — $ — Short-term investments – commercial paper 3,974 — 3,974 — Short-term investments – corporate bonds 24,575 — 24,575 — Short-term investments – municipal bonds 5,025 — 5,025 — Long-term investments – corporate bonds 21,186 — 21,186 — Long-term investments – municipal bonds 5,811 — 5,811 — Total Assets $ 86,627 $ 26,056 $ 60,571 $ — Total Liabilities $ — $ — $ — $ — December 31, 2014 Assets Money market funds $ 17,156 $ 17,156 $ — $ — Other cash equivalents – commercial paper 2,500 — 2,500 — Short-term investments – commercial paper 4,494 — 4,494 — Short-term investments – certificate of deposit 500 — 500 — Short-term investments – corporate bonds 14,357 — 14,357 — Short-term investments – municipal bonds 1,905 — 1,905 — Long-term investments 7,344 — 7,344 — Total Assets $ 48,256 $ 17,156 $ 31,100 $ — Total Liabilities $ — $ — $ — $ —

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Investments at Fair Value	The Company’s available-for-sale investments at fair value consisted of the following at December 31, 2015 and 2014: December 31, 2015 Cost Gross Gross Estimated (In thousands) Short-term investments – commercial paper $ 3,973 $ — $ 1 $ 3,974 Short-term investments – corporate bonds 24,600 (25) — 24,575 Short-term investments – municipal bonds 5,025 — — 5,025 Total short-term investments 33,598 (25) 1 33,574 Long-term investments – corporate bonds 21,289 (103) — 21,186 Long-term investments – municipal bonds 5,818 (9) 2 5,811 Total long-term investments 27,107 (112) 2 26,997 Total investments $ 60,705 $ (137) $ 3 $ 60,571 December 31, 2014 Cost Gross Gross Estimated (In thousands) Short-term investments – commercial paper $ 4,493 $ — $ 1 $ 4,494 Short-term investments – certificate of deposit 500 — — 500 Short-term investments – corporate bonds 14,364 (7) — 14,357 Short-term investments – municipal bonds 1,906 (1) — 1,905 Total short-term investments 21,263 (8) 1 21,256 Long-term investments – corporate bonds 7,354 (10) — 7,344 Total long-term investments 7,354 (10) — 7,344 Total investments $ 28,617 $ (18) $ 1 $ 28,600

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Tabular Disclosure of Major Components of Property and Equipment and Related Accumulated Depreciation	At December 31, 2015 and 2014, net property and equipment at cost consisted of the following: December 31, 2015 2014 (In thousands) Leasehold improvements $ 603 $ 525 Laboratory equipment and other 4,543 3,884 Total property and equipment, at cost 5,146 4,409 Less: Accumulated depreciation and amortization 3,454 3,103 Property and equipment, net $ 1,692 $ 1,306

Note Payable and Accrued Expe28

Note Payable and Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2015
Payables and Accruals [Abstract]
Schedule of Aggregate Future Minimum Payments Due Under Loan and Security Agreement	Aggregate future minimum payments, reflecting payments on outstanding principal plus interest, due under the loan and security agreement as of December 31, 2015, were as follows (in thousands): Year ending December 31, 2016 $ 333 2017 333 2018 219 Total minimum payments 885 Less amount representing interest (126 ) Notes payable, gross 759 Unamortized facility fee (17 ) Accrual of final payment 20 Notes payable, balance 762 Less current portion of notes payable (261 ) Non-current portion of notes payable $ 501
Accrued Expenses	At December 31, 2015 and 2014, accrued expenses consisted of the following: December 31, 2015 2014 (In thousands) Payroll and related costs $ 2,325 $ 1,453 Clinical and nonclinical trial expenses 1,339 2,068 Cost of regaining rights to cancer program — 251 Professional and consulting fees 425 530 Other 185 158 $ 4,274 $ 4,460

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Warrants Outstanding and Exercisable for the Purchase of Common Stock	The Company has the following warrants outstanding and exercisable for the purchase of common stock at December 31, 2015: Expiration Date Shares Weighted November 4, 2016 2,810,650 $ 1.46 November 9, 2017 7,252,081 0.70 May 7, 2018 22,306,327 0.47 May 7, 2020 15,816,327 0.01 September 30, 2020 4,175,975 0.01 February 10, 2021 2,158,750 0.01 Total 54,520,110 0.36
Summary of Stock Options	The following table summarizes information related to the outstanding and exercisable options during 2015 (in thousands, except per share amounts and years): Stock Weighted-Average Weighted-Average Aggregate Outstanding at December 31, 2014 16,951 $ 3.56 Granted 3,534 3.74 Exercised (406 ) 1.44 Forfeited (2,518 ) 3.81 Expired (1,300 ) 5.65 Outstanding at December 31, 2015 16,261 3.45 7.68 $ 8,274 Exercisable at December 31, 2015 8,149 3.50 6.37 6,640 Total exercisable or expected to vest 15,563 3.45 7.62 8,134

Common Stock Warrant and Opti30

Common Stock Warrant and Option Exercises and Employee Stock Purchases (Tables)	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Schedule of Common Stock Warrant and Option Exercises and Employee Stock Purchases	The Company issued 3,402,000, 5,932,000 and 7,346,000 shares of common stock and received total proceeds of $2,546,000, $8,456,000 and $3,527,000 for warrant and stock option exercises and employee stock purchases under the Stock Purchase Plan during the years ended December 31, 2015, 2014 and 2013, respectively, as follows: 2015 2014 2013 (In thousands) Shares Proceeds Shares Proceeds Shares Proceeds Warrant exercises 2,968 $ 1,888 5,544 $ 7,534 7,160 $ 3,318 Stock option exercises 406 584 374 890 171 198 Employee stock purchases 28 74 14 32 15 11 Total 3,402 $ 2,546 5,932 $ 8,456 7,346 $ 3,527

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Commitments Under Company Lease Agreement	The leases are classified as operating leases. Future minimum commitments as of December 31, 2015 under the Company’s lease agreements are approximately: December 31, Operating (In thousands) 2016 $ 1,625 2017 1,174 2018 200 2019 209 2020 88 $ 3,296

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Components of the Deferred Tax Assets	As of December 31, 2015 and 2014, the components of the deferred tax assets are approximately as follows: 2015 2014 (In thousands) Operating loss carryforwards $ 46,432 $ 30,632 Tax credit carryforwards 5,627 2,174 Other 5,698 5,625 57,757 38,431 Valuation allowance (57,757 ) (38,431 ) $ — $ —
Difference Between the 34% U.S. Federal Corporate Tax Rate and the Company's Effective Tax Rate	The difference between the 34% U.S. federal corporate tax rate and the Company’s effective tax rate is as follows for the years ended December 31, 2015, 2014 and 2013: 2015 2014 2013 Expected federal income tax rate (34.0 )% (34.0 )% (34.0 )% Expiring credits and NOLs — — 0.2 Change in valuation allowance 39.8 (115.3 ) 43.1 Federal and state credits (7.4 ) (4.0 ) (5.0 ) State income taxes, net of federal benefit (4.5 ) (5.1 ) (5.1 ) Permanent differences 2.4 0.8 0.9 Section 382 limitation — 157.5 — Other 3.7 0.1 (0.1 ) Effective tax rate 0.0 % 0.0 % 0.0 %

Supplemental Disclosure of Ca33

Supplemental Disclosure of Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Supplemental Disclosure of Cash Flow Information	Supplemental disclosure of cash flow information for the periods presented is as follows: Year Ended December 31, 2015 2014 2013 (In thousands) Supplemental disclosure of cash flow information: Cash paid for interest $ 93 $ 49 $ — Supplemental disclosure of non-cash financing and investing activities: Conversion of Series D preferred stock to common stock $ — $ 5,464 $ — Conversion of Series E preferred stock to common stock $ — $ 5,528 $ — Extinguishment of Series D and Series E preferred stock and issuance of related warrants $ — $ — $ 5,921 Non-cash property additions $ 123 $ 324 $ — Accrued 2013 financing transaction costs paid in 2014 $ — $ — $ 100

April 2013 Pillar Agreements (T

April 2013 Pillar Agreements (Tables)	12 Months Ended
	Dec. 31, 2015
Text Block [Abstract]
Schedule of Assumptions and Other Inputs Used to Compute Fair Value of Agreement Warrants	The Company used the Black-Scholes option pricing model to compute the fair value of the Pillar Warrants as of the May 7, 2013 effective date on which the Pillar Warrants were issued based on the following assumptions and other inputs: Pillar I Additional Common stock price $ 0.57 $ 0.57 Warrant exercise price $ 0.61 $ 0.79 Term of warrant (years) 5.0 1.1 Expected volatility 62 % 67 % Average risk free interest rate 0.8 % 0.1 % Expected dividend yield — — Expected percentage of warrants to be exercised 100 % 100 %

Financings (Tables)

Financings (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure Text Block Supplement [Abstract]
May 2013 Follow-on Underwritten Public Offering	On May 7, 2013, the Company closed a follow-on underwritten public offering, in which it sold 17,500,000 shares of common stock, together with matching warrants to purchase up to 17,500,000 shares of common stock, and pre-funded warrants to purchase up to 15,816,327 shares of common stock, together with matching warrants to purchase up to 15,816,327 shares of common stock, for aggregate gross proceeds of $16.5 million as follows: Combined Common Pre-funded Matching Common stock and matching warrants sold (shares) $ 0.50 17,500,000 — 17,500,000 Pre-funded warrants and matching warrants sold (shares) $ 0.49 — 15,816,327 15,816,327 Total (shares) 17,500,000 15,816,327 33,316,327 Warrant exercise price (per share) — — $ 0.01 $ 0.47 Term of warrant (years) — — 7.0 5.0

Organization - Additional Infor

Organization - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)Platform	Dec. 31, 2014USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of technology platform to develop drug candidates | Platform	2
Accumulated deficit | $	$ (500,081)	$ (451,526)

Summary of Significant Accoun37

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended			36 Months Ended
	Dec. 31, 2015USD ($)Segmentshares	Dec. 31, 2014USD ($)shares	Dec. 31, 2013USD ($)shares	Dec. 31, 2015USD ($)
Accounting Policies [Line Items]
Period of maturities	90 days
Held-to-maturity investments	$ 0	$ 0		$ 0
Realized gains or losses from available-for-sale securities	0	0	$ 0
Losses from investments				0
Auction rate securities	0	0		0
Total restricted cash	$ 311,000	311,000		311,000
Number of operating segments | Segment	1
Stock-based compensation	$ 5,442,000	4,322,000	$ 1,398,000
Accelerated amortization expense associated to employee's option		$ 1,293,000
Options to purchase common stock granted to employees and directors | shares	3,533,750	8,232,424	5,072,583
Fair value of options, vested	$ 5,403,000	$ 4,208,000	$ 1,429,000
Intrinsic value of options exercised	761,000	573,000	$ 150,000
Unrecognized compensation cost related to nonvested stock-based compensation	$ 16,163,000			16,163,000
Period for recognition of cost related to nonvested stock-based compensation arrangements	3 years
Prepaid expenses research and development	$ 2,300,000	$ 840,000		$ 2,300,000
GSK Agreement [Member]
Accounting Policies [Line Items]
Percentage of royalty on net sales	5.00%
GSK Agreement [Member] | License, Research, Clinical Development and Commercialization [Member]
Accounting Policies [Line Items]
Maximum milestone payments	$ 100,000,000
GSK Agreement [Member] | Research and Development Plans and Designation of Development Candidates [Member]
Accounting Policies [Line Items]
Maximum milestone payments	9,000,000
GSK Agreement [Member] | Clinical and Commercial Milestones [Member]
Accounting Policies [Line Items]
Maximum milestone payments	89,000,000
GSK Agreement [Member] | Up-front Payment Arrangement [Member]
Accounting Policies [Line Items]
Upfront payment received under collaboration	$ 2,500,000
Employees [Member]
Accounting Policies [Line Items]
Stock options, vesting period	4 years
Directors [Member]
Accounting Policies [Line Items]
Stock options, vesting period	3 years
Retiring Director's Stock Options [Member]
Accounting Policies [Line Items]
Stock-based compensation	$ 329,000
Minimum [Member]
Accounting Policies [Line Items]
Equipment depreciation period	3 years
Maximum [Member]
Accounting Policies [Line Items]
Equipment depreciation period	5 years

Summary of Significant Accoun38

Summary of Significant Accounting Policies - Change in Accumulated Balance of the Component of Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Accumulated unrealized loss on available-for-sale securities at beginning of period	$ (17)	$ (7)
Change during the period	(117)	(10)	$ (7)
Accumulated unrealized loss on available-for-sale securities at end of period	$ (134)	$ (17)	$ (7)

Summary of Significant Accoun39

Summary of Significant Accounting Policies - Schedule of Assumptions Used to Determine Fair Value of Stock Options Granted During Period (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Average risk free interest rate	1.40%	1.40%	1.30%
Expected dividend yield	0.00%	0.00%	0.00%
Expected lives (years)	4 years 2 months 12 days	4 years 4 months 24 days	5 years
Expected volatility	93.00%	86.00%	67.00%
Weighted average grant date fair value of options granted during the period (per share)	$ 2.51	$ 2.36	$ 0.89
Weighted average exercise price of options granted during the period (per share)	$ 3.74	$ 3.69	$ 1.55

Summary of Significant Accoun40

Summary of Significant Accounting Policies - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	$ 86,627	$ 48,256
Total Liabilities	0	0
Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	26,056	17,156
Other Cash Equivalents - Commercial Paper [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets		2,500
Short-term Investments [Member] | Commercial Paper [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	3,974	4,494
Short-term Investments [Member] | Certificate of Deposit [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets		500
Short-term Investments [Member] | Corporate Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	24,575	14,357
Short-term Investments [Member] | Municipal Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	5,025	1,905
Long-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets		7,344
Long-term Investments [Member] | Corporate Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	21,186
Long-term Investments [Member] | Municipal Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	5,811
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	26,056	17,156
Total Liabilities	0	0
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	26,056	17,156
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	60,571	31,100
Total Liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member] | Other Cash Equivalents - Commercial Paper [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets		2,500
Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member] | Commercial Paper [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	3,974	4,494
Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member] | Certificate of Deposit [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets		500
Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member] | Corporate Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	24,575	14,357
Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member] | Municipal Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	5,025	1,905
Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets		7,344
Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member] | Corporate Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	21,186
Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member] | Municipal Bonds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	5,811
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Assets	0	0
Total Liabilities	$ 0	$ 0

Investments - Summary of Availa

Investments - Summary of Available-for-Sale Investments at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 60,705	$ 28,617
Gross Unrealized (Losses)	(137)	(18)
Gross Unrealized Gains	3	1
Estimated Fair Value	60,571	28,600
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	33,598	21,263
Gross Unrealized (Losses)	(25)	(8)
Gross Unrealized Gains	1	1
Estimated Fair Value	33,574	21,256
Short-term Investments [Member] | Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3,973	4,493
Gross Unrealized Gains	1	1
Estimated Fair Value	3,974	4,494
Short-term Investments [Member] | Certificate of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		500
Estimated Fair Value		500
Short-term Investments [Member] | Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	24,600	14,364
Gross Unrealized (Losses)	(25)	(7)
Estimated Fair Value	24,575	14,357
Short-term Investments [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	5,025	1,906
Gross Unrealized (Losses)		(1)
Estimated Fair Value	5,025	1,905
Long-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	27,107	7,354
Gross Unrealized (Losses)	(112)	(10)
Gross Unrealized Gains	2
Estimated Fair Value	26,997	7,344
Long-term Investments [Member] | Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	21,289	7,354
Gross Unrealized (Losses)	(103)	(10)
Estimated Fair Value	21,186	$ 7,344
Long-term Investments [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	5,818
Gross Unrealized (Losses)	(9)
Gross Unrealized Gains	2
Estimated Fair Value	$ 5,811

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($)	12 Months Ended			36 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Realized gains or losses from available-for-sale securities	$ 0	$ 0	$ 0
Losses from investments				$ 0
Auction rate securities, noncurrent	$ 0	$ 0		$ 0

Property and Equipment - Tabula

Property and Equipment - Tabular Disclosure of Major Components of Property and Equipment and Related Accumulated Depreciation (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Leasehold improvements	$ 603	$ 525
Laboratory equipment and other	4,543	3,884
Total property and equipment, at cost	5,146	4,409
Less: Accumulated depreciation and amortization	3,454	3,103
Property and equipment, net	$ 1,692	$ 1,306

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense on property and equipment	$ 464,000	$ 200,000	$ 137,000

Note Payable and Accrued Expe45

Note Payable and Accrued Expenses - Additional Information (Detail) - Oxford [Member]	12 Months Ended	15 Months Ended
	Dec. 31, 2015USD ($)Installment	Dec. 31, 2015USD ($)Installment
Debt Instrument [Line Items]
Borrowing capacity under the Loan & security agreement	$ 3,000,000	$ 3,000,000
Basis spread on fixed interest rate set at time of advance		7.27%
Minimum interest rate	7.50%	7.50%
Description of interest rate	Each equipment advance includes interest at a fixed interest rate equal to the greater of 7.50% per annum and 7.27% plus the three-month U.S. Libor Rate per annum
Debt instrument payment terms	The principal amount of each equipment advance will be repaid in 36 monthly installments commencing on the applicable amortization date, which was July 1, 2015 for any equipment advance made on or before June 30, 2015. Monthly installments payable prior to July 1, 2015 consisted of interest only and monthly installments payable on or after July 1, 2015 consist of principal and accrued interest
Debt instrument number of installments that include principal payable | Installment	36	36
Final payment of additional interest as a percentage of aggregate amount advanced	5.70%
Weighted average annual effective interest rate	11.10%	11.10%
Minimum prepayment fee interest rate percentage	1.00%
Maximum prepayment fee interest rate percentage	3.00%
Advance received under loan and security agreement	$ 893,000	$ 893,000
Outstanding loan balance, default interest rate	5.00%

Note Payable and Accrued Expe46

Note Payable and Accrued Expenses - Schedule of Aggregate Future Minimum Payments Due Under Loan and Security Agreement (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Debt Instruments [Abstract]
2,016	$ 333
2,017	333
2,018	219
Total minimum payments	885
Less amount representing interest	(126)
Notes payable, gross	759
Unamortized facility fee	(17)
Accrual of final payment	20
Notes payable, balance	762
Notes payable, balance	762
Less current portion of notes payable	(261)	$ (128)
Non-current portion of notes payable	$ 501	$ 742

Note Payable and Accrued Expe47

Note Payable and Accrued Expenses - Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Payroll and related costs	$ 2,325	$ 1,453
Clinical and nonclinical trial expenses	1,339	2,068
Cost of regaining rights to cancer program		251
Professional and consulting fees	425	530
Other	185	158
Total accrued expenses	$ 4,274	$ 4,460

Collaboration and License Agr48

Collaboration and License Agreements - Additional Information (Detail)	Nov. 20, 2015	May. 31, 2014USD ($)	Apr. 30, 2014USD ($)	Dec. 31, 2015USD ($)Targets	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Alliance revenue				$ 249,000	$ 73,000	$ 47,000
Deferred revenue, net of current portion				1,262,000
Abbott Molecular [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Paid or expects to pay for external development expenses		$ 6,700,000		$ 900,000	$ 2,200,000
Expected agreement term		5 years
Merck Sharp [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum amount that may be credited towards any amount due from collaborator for third-party license income received by the Company			$ 60,000,000
Percentage of third-party license income received by the Company that is credited towards any amount due from collaborator			15.00%
GSK Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue recognition period	27 months			27 months
Number of additional target, optional | Targets				2
Maximum royalty percentage on net sales				5.00%
Alliance revenue				$ 100,000
Deferred revenue				2,300,000
Deferred revenue, net of current portion				1,100,000
GSK Agreement [Member] | License, Research, Clinical Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payments				100,000,000
GSK Agreement [Member] | Research and Development Plans and Designation of Development Candidates [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payments				9,000,000
GSK Agreement [Member] | Clinical and Commercial Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payments				89,000,000
GSK Agreement [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Anticipated initial collaboration term	4 years
GSK Agreement [Member] | Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Anticipated initial collaboration term	2 years
Up-front Payment Arrangement [Member] | GSK Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received under collaboration				$ 2,500,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - $ / shares	Feb. 19, 2015	Feb. 06, 2014	May. 07, 2013	May. 05, 1998	Dec. 31, 2014	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 10, 2014	Dec. 31, 2012	Nov. 30, 2012	Nov. 30, 2011
Changes In Equity And Comprehensive Income Line Items [Line Items]
Stock issued, shares	23,000,000					13,727,251
Minimum closing sales price of common stock to issue termination notice to put holders							$ 32
Shares held by put holders							35,780
Remaining shares of common stock subject to the liquidation put							763,954
Common stock, shares reserved for future issuance							79,163,446
Maximum number of additional common shares							6,946,978
Minimum option exercise price as a percentage of market value of common stock							100.00%
Common stock options outstanding					16,951,000		16,261,000	16,951,000
Common shares available for grant							8,120,164
Options outstanding under earlier plans							4,978,802
Grant of inducement stock option							1,150,000	2,600,000
Inducement grants outstanding shares							3,150,000
Minimum Percentage Voting Stock that Prevents Employee Stock Purchase Plan Participation							5.00%
Maximum % of employee defined annualized base pay that may be used to purchase stock under Employee Stock Purchase Plan							15.00%
Preferred stock, shares authorized					5,000,000		5,000,000	5,000,000
Preferred stock, par value					$ 0.01		$ 0.01	$ 0.01
Series A preferred stock liquidation preference per share							1
Series A Preferred stock conversion price per share							$ 34
2013 Stock Incentive Plan [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Common stock, shares reserved for future issuance							15,224,460
Maximum number of shares that may be granted to any one individual in single year							1,500,000
Stock options, expiration period							10 years
Minimum [Member] | 2013 Stock Incentive Plan [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Stock options, vesting period							3 years
Maximum [Member] | 2013 Stock Incentive Plan [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Stock options, vesting period							4 years
Employee Stock Purchase Plan [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Common stock shares authorized for issuance under stock purchase plan							500,000
Percentage of fair market value of common stock used as Employee Stock Purchase Plan option price							85.00%
Minimum % of participating employee's base pay that may be used to purchase stock under Employee Stock Purchase Plan during an offering period							1.00%
Maximum % of participating employee's base pay that may be used to purchase stock under Employee Stock Purchase Plan during an offering period							10.00%
Percentage of Market Value of Common Stock on Commencement of Offering Period							85.00%
Common stock share issued							27,951	13,844	14,716
Series A Preferred Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Preferred stock, par value					$ 0.01		$ 0.01	$ 0.01
Preferred stock, shares designated					1,500,000		1,500,000	1,500,000
Annual percentage of dividend of preferred stock							1.00%
Preferred stock, shares outstanding					1,000		1,000	1,000
Preferred stock, shares issued					1,000		1,000	1,000
Series D Preferred Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Preferred stock, shares outstanding									1,124,000	1,124,260
Preferred stock, shares issued										1,124,260
Series D Preferred Stock [Member] | Pillar One [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Preferred stock, shares outstanding		0
Preferred stock, shares issued													1,124,260
Shares of common stock issued upon conversion		6,266,175
Series E Preferred Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Preferred stock, par value					$ 0.01		$ 0.01	$ 0.01
Preferred stock, shares designated					424,000		0	424,000
Preferred stock, shares outstanding					0		0	0	424,000		424,000
Preferred stock, shares issued					0		0	0
Series E Preferred Stock [Member] | Pillar Two Entities [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Preferred stock, shares outstanding					0			0
Preferred stock, shares issued					0			0				424,242
Shares of common stock issued upon conversion					8,484,840
Common Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Stock issued, shares			17,500,000	1,199,684
Sale price of common shares subject to the liquidation put							$ 16
Price exceeds on number of days							20 days
Liquidation put shares no longer held by original holders							399,950

Stockholders' Equity - Warrants

Stockholders' Equity - Warrants Outstanding and Exercisable for the Purchase of Common Stock (Detail)	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Class of Warrant or Right [Line Items]
Shares | shares	54,520,110
Weighted average exercise price of warrants | $ / shares	$ 0.36
Class of Warrant One [Member]
Class of Warrant or Right [Line Items]
Expiration Date	Nov. 4, 2016
Shares | shares	2,810,650
Weighted average exercise price of warrants | $ / shares	$ 1.46
Class of Warrant Two [Member]
Class of Warrant or Right [Line Items]
Expiration Date	Nov. 9, 2017
Shares | shares	7,252,081
Weighted average exercise price of warrants | $ / shares	$ 0.70
Class of Warrant Three [Member]
Class of Warrant or Right [Line Items]
Expiration Date	May 7, 2018
Shares | shares	22,306,327
Weighted average exercise price of warrants | $ / shares	$ 0.47
Class of Warrant Four [Member]
Class of Warrant or Right [Line Items]
Expiration Date	May 7, 2020
Shares | shares	15,816,327
Weighted average exercise price of warrants | $ / shares	$ 0.01
Class of Warrant Five [Member]
Class of Warrant or Right [Line Items]
Expiration Date	Sep. 30, 2020
Shares | shares	4,175,975
Weighted average exercise price of warrants | $ / shares	$ 0.01
Class of Warrant Six [Member]
Class of Warrant or Right [Line Items]
Expiration Date	Feb. 10, 2021
Shares | shares	2,158,750
Weighted average exercise price of warrants | $ / shares	$ 0.01

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Options (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Options, Outstanding, Beginning Balance	16,951
Granted	3,534
Exercised	(406)
Forfeited	(2,518)
Expired	(1,300)
Options, Outstanding, Ending Balance	16,261	16,951
Exercisable, Ending Balance	8,149
Total exercisable or expected to vest	15,563
Weighted Average Exercise Price, Beginning Balance	$ 3.56
Granted, Weighted Average Exercise Price	3.74	$ 3.69	$ 1.55
Exercised, Weighted Average Exercise Price	1.44
Forfeited, Weighted Average Exercise Price	3.81
Expired, Weighted Average Exercise Price	5.65
Weighted Average Exercise Price, Ending Balance	3.45	$ 3.56
Exercisable, Weighted Average Exercise Price	3.50
Total exercisable or expected to vest, Weighted Average Exercise Price	$ 3.45
Outstanding, Ending balance, Weighted Average Remaining Contractual Term	7 years 8 months 5 days
Exercisable Ending Balance, Weighted Average Remaining Contractual Term	6 years 4 months 13 days
Total exercisable or expected to vest, Weighted Average Remaining Contractual Term	7 years 7 months 13 days
Outstanding, Intrinsic Value, Ending Balance	$ 8,274
Exercisable, Ending Balance, Intrinsic Value	6,640
Total exercisable or expected to vest, Aggregate Intrinsic Value	$ 8,134

Common Stock Warrant and Opti52

Common Stock Warrant and Option Exercises and Employee Stock Purchases - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Warrant and Option Exercises and Employee Stock Purchases [Line Items]
Number of shares of common stock issued for stock warrants and stock options exercised and ESPP purchases	3,402,000	5,932,000	7,346,000
Proceeds from stock issued for warrant and option exercises & ESPP purchases	$ 2,546	$ 8,456	$ 3,527
Common Stock Warrants and Option Exercises and Employee Stock Purchases [Member]
Warrant and Option Exercises and Employee Stock Purchases [Line Items]
Number of shares of common stock issued for stock warrants and stock options exercised and ESPP purchases	3,402,000	5,932,000	7,346,000
Proceeds from stock issued for warrant and option exercises & ESPP purchases	$ 2,546	$ 8,456	$ 3,527

Common Stock Warrant and Opti53

Common Stock Warrant and Option Exercises and Employee Stock Purchases - Schedule of Common Stock Warrant and Option Exercises and Employee Stock Purchases (Detail) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Warrant and Option Exercises and Employee Stock Purchases [Line Items]
Total, Shares	3,402	5,932	7,346
Total, Proceeds	$ 2,546	$ 8,456	$ 3,527
Warrant Exercises [Member]
Warrant and Option Exercises and Employee Stock Purchases [Line Items]
Total, Shares	2,968	5,544	7,160
Total, Proceeds	$ 1,888	$ 7,534	$ 3,318
Stock Option Exercises [Member]
Warrant and Option Exercises and Employee Stock Purchases [Line Items]
Total, Shares	406	374	171
Total, Proceeds	$ 584	$ 890	$ 198
Employee Stock Purchases [Member]
Warrant and Option Exercises and Employee Stock Purchases [Line Items]
Total, Shares	28	14	15
Total, Proceeds	$ 74	$ 32	$ 11

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Sep. 30, 2013	May. 07, 2013	Dec. 31, 2014	Feb. 28, 2014	Nov. 30, 2012	Nov. 30, 2011	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 10, 2014
Contingencies And Commitments [Line Items]
Rent expense, including real estate taxes							$ 1,744,000	$ 1,672,000	$ 1,601,000
Cash restricted for a security deposit							311,000
Annual minimum payments due, 2016							10,000
Future minimum commitments under agreement, total							$ 3,077,000
Warrant to purchase common stock							54,520,110
Number of shares of common stock sold in financing		17,500,000
Proceeds from issuance of common stock in lieu of director board and committee fees							$ 122,000	$ 82,000	$ 26,000
Cambridge Facility [Member]
Contingencies And Commitments [Line Items]
Period of renewal option exercisable by the Company							3 years
Operating lease expiration date							Aug. 31, 2017
Exton Facility [Member]
Contingencies And Commitments [Line Items]
Period of renewal option exercisable by the Company							3 years
Operating lease expiration date							May 31, 2020
Series E Preferred Stock [Member]
Contingencies And Commitments [Line Items]
Preferred stock, shares issued			0				0	0
Series D Preferred Stock [Member]
Contingencies And Commitments [Line Items]
Preferred stock, shares issued										1,124,260
Common Stock and Matching Warrants Sold [Member]
Contingencies And Commitments [Line Items]
Number of shares of common stock sold in financing		17,500,000
Pillar Three Entities [Member]
Contingencies And Commitments [Line Items]
Exercise price of warrants		$ 0.47
Aggregate purchase price		$ 2,500,000
Shares issued on exercise of warrants during the period							2,600,000	500,000
Proceeds from exercise of warrants							$ 1,222,000	$ 235,000
Pillar Three Entities [Member] | Common Stock and Matching Warrants Sold [Member]
Contingencies And Commitments [Line Items]
Warrant to purchase common stock		5,000,000
Number of shares of common stock sold in financing		5,000,000
Pillar Four Entities [Member]
Contingencies And Commitments [Line Items]
Number of shares of common stock sold in financing	1,774,193
Aggregate purchase price	$ 2,750,000
Pillar Two Entities [Member]
Contingencies And Commitments [Line Items]
Shares issued on exercise of warrants during the period							232,759	1,424,242
Proceeds from exercise of warrants							$ 163,000	$ 1,035,000
Pillar Two Entities [Member] | Series E Preferred Stock [Member]
Contingencies And Commitments [Line Items]
Preferred stock, shares issued			0		424,242			0
Aggregate purchase price under agreement					$ 7,000,000
Conversion of preferred stock to common, shares			8,484,840
Pillar Two Entities [Member] | Common Stock [Member] | Series E Warrant [Member]
Contingencies And Commitments [Line Items]
Warrant to purchase common stock					8,484,840
Exercise price of warrants					$ 0.70
Warrants expiration date							Nov. 9, 2017
Pillar One [Member]
Contingencies And Commitments [Line Items]
Shares issued on exercise of warrants during the period								1,575,758
Proceeds from exercise of warrants								$ 1,065,000
Pillar One [Member] | Series D Preferred Stock [Member]
Contingencies And Commitments [Line Items]
Preferred stock, shares issued						1,124,260
Aggregate purchase price under agreement						$ 9,500,000
Conversion of preferred stock to common, shares				6,266,175
Pillar One [Member] | Common Stock [Member] | Series D Warrant [Member]
Contingencies And Commitments [Line Items]
Warrant to purchase common stock						2,810,650
Exercise price of warrants					$ 1.46	$ 1.63
Warrants expiration date							Nov. 4, 2016

Commitments and Contingencies55

Commitments and Contingencies - Future Minimum Commitments Under Company Lease Agreement (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,016	$ 1,625
2,017	1,174
2,018	200
2,019	209
2,020	88
Total	$ 3,296

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax [Line Items]
Period over which NOL and tax credit carryforward limitations are applied	1 year
Period of cumulative changes in ownership	3 years
Cumulative changes in ownership	50.00%
Operating loss carryforwards expiration year	2,035
Expected federal income tax rate	(34.00%)	(34.00%)	(34.00%)
Unrecognized tax benefits from uncertain tax	$ 0	$ 0
Years not subject to income tax examination	Tax examinations for years before 2012
Period over which material changes in unrecognized tax positions are not expected	12 months
Federal [Member]
Income Tax [Line Items]
Cumulative net operating loss carryforwards	$ 120,960,000
Tax credit carryforwards	$ 4,923,000
Tax credit carryforward expiration year	2,035
Excess tax benefit deductions related to the exercise of stock options	$ 993,000
State [Member]
Income Tax [Line Items]
Cumulative net operating loss carryforwards	114,059,000
Tax credit carryforwards	$ 1,065,000
Tax credit carryforward expiration year	2,030
Excess tax benefit deductions related to the exercise of stock options	$ 654,000

Income Taxes - Components of th

Income Taxes - Components of the Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Operating loss carryforwards	$ 46,432	$ 30,632
Tax credit carryforwards	5,627	2,174
Other	5,698	5,625
Deferred Tax Assets, Gross	57,757	38,431
Valuation allowance	(57,757)	(38,431)
Deferred Tax Assets, Net	$ 0	$ 0

Income Taxes - Difference Betwe

Income Taxes - Difference Between the 34% U.S. Federal Corporate Tax Rate and the Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Expected federal income tax rate	(34.00%)	(34.00%)	(34.00%)
Expiring credits and NOLs			0.20%
Change in valuation allowance	39.80%	(115.30%)	43.10%
Federal and state credits	(7.40%)	(4.00%)	(5.00%)
State income taxes, net of federal benefit	(4.50%)	(5.10%)	(5.10%)
Permanent differences	2.40%	0.80%	0.90%
Section 382 limitation		157.50%
Other	3.70%	0.10%	(0.10%)
Effective tax rate	0.00%	0.00%	0.00%

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Maximum employer match as a percentage of base pay	3.00%
Portion of the first 6% of employees' contributions	50.00%
Portion of the Employee's base salary that the Company matches	6.00%
Employer matching contributions to the plan	$ 217,000	$ 139,000	$ 83,000

Net Loss per Common Share App60

Net Loss per Common Share Applicable to Common Stockholders - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Total antidilutive securities	70,782,788	74,640,383
Preferred stock dividends		$ 519,000	$ 2,866,000
Series D Preferred Stock [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Preferred stock dividends		66,000
Series E Preferred Stock [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Preferred stock dividends		$ 453,000

Supplemental Disclosure of Ca61

Supplemental Disclosure of Cash Flow Information - Supplemental Disclosure of Cash Flow Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental disclosure of cash flow information:
Cash paid for interest	$ 93	$ 49
Supplemental disclosure of non-cash financing and investing activities:
Non-cash property additions	$ 123	324
Accrued 2013 financing transaction costs paid in 2014			$ 100
Series D Preferred Stock [Member]
Supplemental disclosure of non-cash financing and investing activities:
Conversion of preferred stock to common stock		5,464
Series E Preferred Stock [Member]
Supplemental disclosure of non-cash financing and investing activities:
Conversion of preferred stock to common stock		$ 5,528
Series D and E Preferred Stock [Member]
Supplemental disclosure of non-cash financing and investing activities:
Extinguishment of Series D and Series E preferred stock and issuance of related warrants			$ 5,921

April 2013 Pillar Agreements -

April 2013 Pillar Agreements - Additional Information (Detail)	May. 07, 2013USD ($)$ / shares$ / Reporting_Unit	Apr. 22, 2013$ / shares$ / Reporting_Unitshares	Apr. 30, 2013Agreement$ / sharesshares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)
Effects of Agreements [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued | shares				54,520,110
Minimum closing price to redeem the warrants | $ / Reporting_Unit	2.80
Redemption price per share of warrants | $ / Reporting_Unit	0.01
Fair value of the Pillar Warrants in equity	$ 380,000
Extinguishment loss which was immediately charged to net loss applicable to common stockholders	1,750,000
Increase in stockholders equity resulting from preferred stock extinguishment and warrant issuance	$ 5,921,000
Minimum period for determining expected volatility				3 years
Percentage of holding by affiliates above which warrants may not be exercised				19.99%
Pillar I Warrants [Member]
Effects of Agreements [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued | shares		1,000,000
Exercise price of warrants | $ / shares	$ 0.61	$ 0.61
Minimum closing price to redeem the warrants | $ / Reporting_Unit		2.80
Redemption price per share of warrants | $ / Reporting_Unit		0.01
Additional Pillar Warrants [Member]
Effects of Agreements [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued | shares			1,000,000
Exercise price of warrants | $ / shares	$ 0.79		$ 0.79
Final exercise date of warrant			Jun. 1, 2014
Series D Preferred Stock [Member]
Effects of Agreements [Line Items]
Carrying value of preferred stock prior to extinguishment	$ 5,921,000
Carrying value of preferred stock	5,464,000
Series E Preferred Stock [Member]
Effects of Agreements [Line Items]
Carrying value of preferred stock prior to extinguishment	3,701,000
Carrying value of preferred stock	$ 5,528,000			$ 0	$ 0
April 2013 Pillar Agreements [Member]
Effects of Agreements [Line Items]
Number of agreements | Agreement			2
April 2013 Pillar Agreements [Member] | Series D Preferred Stock [Member] | Minimum [Member]
Effects of Agreements [Line Items]
Unaffiliated ownership % that would trigger the right to require the Company to repurchase stock that was waived by Pillar Agreement			66.67%
April 2013 Pillar Agreements [Member] | Series D And Series E Preferred Stock [Member]
Effects of Agreements [Line Items]
Percentage of preferred stock holders who waived right to receive specified amount in liquidation			100.00%

April 2013 Pillar Agreements 63

April 2013 Pillar Agreements - Schedule of Assumptions and Other Inputs Used to Compute Fair Value of Agreement Warrants (Detail) - $ / shares	May. 07, 2013	Feb. 19, 2015	Apr. 30, 2013	Apr. 22, 2013
Assumptions used to compute fair value of Pillar warrants [Line Items]
Common stock price		$ 3.75
Pillar I Warrants [Member]
Assumptions used to compute fair value of Pillar warrants [Line Items]
Common stock price	$ 0.57
Warrant exercise price	$ 0.61			$ 0.61
Term of warrant (years)	5 years
Expected volatility	62.00%
Average risk free interest rate	0.80%
Expected dividend yield	0.00%
Expected percentage of warrants to be exercised	100.00%
Additional Pillar Warrants [Member]
Assumptions used to compute fair value of Pillar warrants [Line Items]
Common stock price	$ 0.57
Warrant exercise price	$ 0.79		$ 0.79
Term of warrant (years)	1 year 1 month 6 days
Expected volatility	67.00%
Average risk free interest rate	0.10%
Expected dividend yield	0.00%
Expected percentage of warrants to be exercised	100.00%

Financings - Additional Informa

Financings - Additional Information 1 (Detail) - USD ($) $ / shares in Units, $ in Millions	Feb. 19, 2015	Sep. 30, 2013	Dec. 31, 2015	Feb. 10, 2014	May. 07, 2013
Class of Stock [Line Items]
Stock issued, shares	23,000,000	13,727,251
Common stock, price per share	$ 3.75
Gross proceeds from offering of common stock	$ 86.3
Net proceeds from offering of common stock	$ 80.6
Shares of common stock that may be purchased upon exercise of warrants			54,520,110
Pre-funded Warrants [Member]
Class of Stock [Line Items]
Warrant exercise price per share		$ 0.01		$ 0.01	$ 0.01
Shares of common stock that may be purchased upon exercise of warrants		4,175,975		2,158,750	15,816,327
Investment Funds [Member] | Directors [Member]
Class of Stock [Line Items]
Stock issued, shares	5,333,333
Common stock, price per share	$ 3.75
Baker Bros. Advisors LP [Member]
Class of Stock [Line Items]
Common stock held, shares	6,965,432
Shares of common stock that may be purchased upon exercise of warrants	20,316,327
Warrant exercise price per share	$ 0.47
Baker Bros. Advisors LP [Member] | Pre-funded Warrants [Member]
Class of Stock [Line Items]
Warrant exercise price per share	$ 0.01
Shares of common stock that may be purchased upon exercise of warrants	22,151,052

Financings - Additional Infor65

Financings - Additional Information 2 (Detail) - USD ($) $ / shares in Units, $ in Millions	Feb. 19, 2015	Feb. 10, 2014	May. 07, 2013	Sep. 30, 2013	Dec. 31, 2015
Class of Stock [Line Items]
Stock issued, shares	23,000,000			13,727,251
Shares of common stock that may be purchased upon exercise of warrants issued					54,520,110
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any		$ 40.1	$ 16.5	$ 27.7
Price to the public per share of common stock		$ 4		$ 1.55
Sales price per share of pre-funded warrants		$ 3.99		$ 1.54
Net proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any		$ 37.2	$ 14.5	$ 25.7
Common Stock [Member]
Class of Stock [Line Items]
Stock issued, shares		7,867,438
Pre-funded Warrants [Member]
Class of Stock [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued		2,158,750	15,816,327	4,175,975
Exercise price of warrants		$ 0.01	$ 0.01	$ 0.01
Pre-funded warrants expiration date		Feb. 10, 2021		Sep. 30, 2020

Financings - Additional Infor66

Financings - Additional Information 3 (Detail) - USD ($) $ / shares in Units, $ in Millions	Feb. 19, 2015	Feb. 10, 2014	May. 07, 2013	Sep. 30, 2013	Dec. 31, 2015
Class of Stock [Line Items]
Stock issued, shares	23,000,000			13,727,251
Shares of common stock that may be purchased upon exercise of warrants issued					54,520,110
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any		$ 40.1	$ 16.5	$ 27.7
Price to the public per share of common stock		$ 4		$ 1.55
Sales price per share of pre-funded warrants		$ 3.99		$ 1.54
Net proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any		$ 37.2	$ 14.5	$ 25.7
Pre-funded Warrants [Member]
Class of Stock [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued		2,158,750	15,816,327	4,175,975
Exercise price of warrants		$ 0.01	$ 0.01	$ 0.01
Pre-funded warrants expiration date		Feb. 10, 2021		Sep. 30, 2020

Financings - Additional Infor67

Financings - Additional Information 4 (Detail) - USD ($) $ in Millions	Feb. 19, 2015	Feb. 10, 2014	May. 07, 2013	May. 05, 1998	Sep. 30, 2013	Dec. 31, 2015
Class of Stock [Line Items]
Stock issued, shares	23,000,000				13,727,251
Shares of common stock that may be purchased upon exercise of warrants issued						54,520,110
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any		$ 40.1	$ 16.5		$ 27.7
Pre-funded Warrants [Member]
Class of Stock [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued			15,816,327
Matching Warrants [Member]
Class of Stock [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued			33,316,327
Matching Warrants [Member] | Pre-funded Warrants [Member]
Class of Stock [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued			15,816,327
Common Stock [Member]
Class of Stock [Line Items]
Stock issued, shares			17,500,000	1,199,684
Common Stock [Member] | Matching Warrants [Member]
Class of Stock [Line Items]
Shares of common stock that may be purchased upon exercise of warrants issued			17,500,000

Financings - May 2013 Follow-on

Financings - May 2013 Follow-on Underwritten Public Offering (Detail) - $ / shares	May. 07, 2013	Dec. 31, 2015	Feb. 19, 2015	Feb. 10, 2014	Sep. 30, 2013
Class of Warrant or Right [Line Items]
Price to the public (per share of common stock)			$ 3.75
Number of shares of common stock sold in financing	17,500,000
Total (shares)		54,520,110
Common Stock and Matching Warrants Sold [Member]
Class of Warrant or Right [Line Items]
Price to the public (per share of common stock)	$ 0.50
Number of shares of common stock sold in financing	17,500,000
Pre-funded Warrants & Matching Warrants Sold [Member]
Class of Warrant or Right [Line Items]
Price to the public (per share of common stock)	$ 0.49
Matching Warrants [Member]
Class of Warrant or Right [Line Items]
Total (shares)	33,316,327
Warrant exercise price (per share)	$ 0.47
Term of warrant (years)	5 years
Matching Warrants [Member] | Common Stock and Matching Warrants Sold [Member]
Class of Warrant or Right [Line Items]
Total (shares)	17,500,000
Matching Warrants [Member] | Pre-funded Warrants & Matching Warrants Sold [Member]
Class of Warrant or Right [Line Items]
Total (shares)	15,816,327
Pre-funded Warrants [Member]
Class of Warrant or Right [Line Items]
Total (shares)	15,816,327			2,158,750	4,175,975
Warrant exercise price (per share)	$ 0.01			$ 0.01	$ 0.01
Term of warrant (years)	7 years
Pre-funded Warrants [Member] | Pre-funded Warrants & Matching Warrants Sold [Member]
Class of Warrant or Right [Line Items]
Total (shares)	15,816,327

Financings - Additional Infor69

Financings - Additional Information 5 (Detail) $ in Millions	Feb. 10, 2014USD ($)	May. 07, 2013USD ($)$ / Reporting_Unit	Sep. 30, 2013USD ($)
Equity [Abstract]
Net proceeds from sale of common stock and warrants excluding the proceeds from future exercise of the warrants, if any | $	$ 37.2	$ 14.5	$ 25.7
Redemption price per share of warrants		0.01
Notice period to holder prior to redemption of warrants by Company		30 days
Minimum trading days considered to redeem warrants		20 days
Maximum trading days considered to redeem warrants		30 days
Minimum closing price to redeem the warrants		2.80

Registration Rights Agreement -

Registration Rights Agreement - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Registration rights agreement date	Feb. 9, 2015
Registration statement filing period with SEC	60 days