Viracta Therapeutics (VIRX) 10-K 9 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 01, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	SNSS
Entity Registrant Name	SUNESIS PHARMACEUTICALS INC
Entity Central Index Key	1,061,027
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	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		34,348,917
Entity Public Float			$ 58,850,769

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 26,977	$ 8,056
Marketable securities	4,773	34,532
Prepaids and other current assets	1,183	643
Total current assets	32,933	43,231
Property and equipment, net	20	3
Deposits and other assets	1,381
Total assets	34,334	43,234
Current liabilities:
Accounts payable	1,697	1,871
Accrued clinical expense	767	1,434
Accrued compensation	1,440	2,000
Other accrued liabilities	1,570	1,691
Current portion of deferred revenue		610
Current portion of notes payable	7,204	3,333
Total current liabilities	12,678	10,939
Non-current portion of notes payable		11,102
Other liabilities	112	169
Commitments and contingencies (Note 9)
Stockholders’ equity:
Convertible preferred stock, $0.0001 par value; 10,000 shares authorized as of December 31, 2017; 18 shares issued and outstanding as of December 31, 2017 and 2016	20,966	18,808
Common stock, $0.0001 par value; 400,000 shares authorized as of December 31, 2017; 34,291 and 20,925 shares issued and outstanding as of December 31, 2017 and 2016, respectively	3	2
Additional paid-in capital	633,436	599,632
Accumulated other comprehensive loss	(7)	(22)
Accumulated deficit	(632,854)	(597,396)
Total stockholders’ equity	21,544	21,024
Total liabilities and stockholders’ equity	$ 34,334	$ 43,234

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	18,000	18,000
Preferred stock, shares outstanding	17,697	17,897
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	34,291,000	20,925,000
Common stock, shares outstanding	34,291,000	20,925,000

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
License and other revenue	$ 669	$ 2,536	$ 3,061
Total revenues	669	2,536	3,061
Operating expenses:
Research and development	21,540	22,881	23,701
General and administrative	13,548	16,115	18,662
Total operating expenses	35,088	38,996	42,363
Loss from operations	(34,419)	(36,460)	(39,302)
Interest expense	(1,396)	(1,721)	(939)
Other income, net	357	158	3,565
Net loss	(35,458)	(38,023)	(36,676)
Unrealized gain (loss) on available-for-sale securities	15	(11)	(4)
Comprehensive loss	(35,443)	(38,034)	(36,680)
Net loss:
Basic	(35,458)	(38,023)	(36,676)
Diluted	$ (35,458)	$ (38,023)	$ (36,676)
Shares used in computing net loss per common share:
Basic	24,516	15,688	12,156
Diluted	24,516	15,688	12,156
Net loss per common share:
Basic	$ (1.45)	$ (2.42)	$ (3.02)
Diluted	$ (1.45)	$ (2.42)	$ (3.02)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2014	$ 13,802		$ 1	$ 536,505	$ (7)	$ (522,697)
Beginning Balance, shares at Dec. 31, 2014			11,017,000
Issuance of common stock in underwritten offering, net of issuance costs	8,709			8,709
Issuance of common stock in underwritten offering, net of issuance costs, shares			1,833,000
Issuance of common stock through controlled equity offering facilities, net of issuance costs	18,125			18,125
Issuance of common stock through controlled equity offering facilities, net of issuance costs, shares			1,160,000
Issuance of common stock pursuant to warrant exercises, shares			350,000
Issuance of common stock pursuant to stock option exercises	331			331
Issuance of common stock pursuant to stock option exercises, shares			28,000
Issuance of common stock under employee stock purchase plans	202			202
Issuance of common stock under employee stock purchase plans, shares			22,000
Issuance of common stock to employees, shares			10,000
Issuance of preferred stock	16,459	$ 16,459
Issuance of preferred stock, shares		20,000
Issuance of warrants to purchase common stock	100			100
Stock-based compensation expenses—employees	6,149			6,149
Stock-based compensation expenses—non- employees	196			196
Net loss	(36,676)					(36,676)
Unrealized gain (loss) on available-for-sale securities	(4)				(4)
Ending Balance at Dec. 31, 2015	27,393	$ 16,459	$ 1	570,317	(11)	(559,373)
Ending Balance, shares at Dec. 31, 2015		20,000	14,420,000
Issuance of common stock in underwritten offering, net of issuance costs	20,325		$ 1	20,324
Issuance of common stock in underwritten offering, net of issuance costs, shares			5,676,000
Issuance of common stock through controlled equity offering facilities, net of issuance costs	269			269
Issuance of common stock through controlled equity offering facilities, net of issuance costs, shares			57,000
Issuance of common stock upon conversion of preferred stock		$ (3,243)		3,243
Issuance of common stock upon conversion of preferred stock, shares		(4,000)	644,000
Issuance of common stock under employee stock purchase plans	$ 152			152
Issuance of common stock under employee stock purchase plans, shares	59,086		129,000
Issuance of preferred stock	$ 5,592	$ 5,592
Issuance of preferred stock, shares		2,000
Issuance of warrants to purchase common stock	536			536
Stock-based compensation expenses—employees	4,600			4,600
Stock-based compensation expenses—non- employees	191			191
Net loss	(38,023)					(38,023)
Unrealized gain (loss) on available-for-sale securities	(11)				(11)
Ending Balance at Dec. 31, 2016	$ 21,024	$ 18,808	$ 2	599,632	(22)	(597,396)
Ending Balance, shares at Dec. 31, 2016	20,925,000	18,000	20,925,000
Issuance of common stock, preferred stock and warrants in underwritten offering, net of issuance costs	$ 18,510	$ 4,426	$ 1	14,083
Issuance of common stock, preferred stock and warrants in underwritten offering, net of issuance costs, shares		3,000	7,500,000
Issuance of common stock through controlled equity offering facilities, net of issuance costs	14,179			14,179
Issuance of common stock through controlled equity offering facilities, net of issuance costs, shares			5,321,000
Issuance of common stock upon conversion of preferred stock		$ (2,268)		2,268
Issuance of common stock upon conversion of preferred stock, shares		(3,000)	450,000
Issuance of common stock pursuant to stock option exercises	$ 24			24
Issuance of common stock pursuant to stock option exercises, shares	8,000		8,000
Issuance of common stock under employee stock purchase plans	$ 217			217
Issuance of common stock under employee stock purchase plans, shares	87,020		87,000
Stock-based compensation expenses—employees	$ 2,924			2,924
Stock-based compensation expenses—non- employees	109			109
Net loss	(35,458)					(35,458)
Unrealized gain (loss) on available-for-sale securities	15				15
Ending Balance at Dec. 31, 2017	$ 21,544	$ 20,966	$ 3	$ 633,436	$ (7)	$ (632,854)
Ending Balance, shares at Dec. 31, 2017	34,291,000	18,000	34,291,000

CONSOLIDATED STATEMENTS OF STO6

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Stockholders Equity [Abstract]
Issuance of common stock in underwritten offering	$ 15,000	$ 21,852	$ 9,236
Issuance of preferred stock and warrants in underwritten offering	5,000
Issuance of common stock, preferred stock and warrants in underwritten offering, issuance cost	1,500
Issuance of common stock in underwritten offering, issuance costs		1,497	527
Issuance of common stock through controlled equity offering facilities	14,468	269	18,564
Issuance of common stock through controlled equity offering facilities, issuance costs	$ 289	$ 5	$ 439

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net loss	$ (35,458)	$ (38,023)	$ (36,676)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	3,033	4,791	6,345
Depreciation and amortization	9	11	27
Amortization of debt discount and debt issuance costs	269	359	135
Write-off debt discount upon note repayment		27
Decrease in fair value of warrant liability			(3,543)
Changes in operating assets and liabilities:
Prepaids and other assets	(1,921)	(85)	660
Accounts payable	(174)	(582)	(724)
Accrued clinical expense	(667)	(520)	(1,158)
Accrued compensation	(560)	394	(681)
Other liabilities	61	169
Other accrued liabilities	(124)	(1,062)	(186)
Deferred revenue	(610)	(2,441)	(2,930)
Net cash used in operating activities	(36,142)	(36,962)	(38,731)
Cash flows from investing activities
Purchases of property and equipment	(26)
Purchases of marketable securities		(35,530)	(35,683)
Sale and maturities of marketable securities	29,774	20,531	36,930
Net cash provided by (used in) investing activities	29,748	(14,999)	1,247
Cash flows from financing activities
Proceeds from notes payable		15,000
Principal payments on notes payable and final payment	(7,615)	(7,983)	(1,642)
Payment of financing fees and debt issuance costs		(266)
Proceeds from issuance of convertible preferred stock offering, net	4,633	5,592	16,459
Proceeds from issuance of common stock, net	13,877	20,367	8,709
Proceeds from issuance of common stock through controlled equity offering facilities, net	14,179	269	18,125
Proceeds from exercise of warrants, stock options and stock purchase rights	241	152	533
Net cash provided by financing activities	25,315	33,131	42,184
Net increase (decrease) in cash and cash equivalents	18,921	(18,830)	4,700
Cash and cash equivalents at beginning of period	8,056	26,886	22,186
Cash and cash equivalents at end of period	26,977	8,056	26,886
Supplemental disclosure of cash flow information
Interest paid	1,066	1,239	631
Supplemental disclosure of non-cash activities
Transfer of fair value of exercised warrants to additional paid-in capital			100
Conversion of preferred stock to common stock	$ (2,268)	(3,243)
Fair value of warrants issued in connection with notes payable		$ 536
Cashless exercise of warrants			$ 4,486

Company Overview

Company Overview	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Company Overview	1. Company Overview Description of Business Sunesis Pharmaceutical, Inc. (“Sunesis” or the “Company”) is a biopharmaceutical company focused on the development and commercialization of new oncology therapeutics for the treatment of cancer. The Company’s primary activities since incorporation have been conducting research and development internally and through corporate collaborators, in-licensing and out-licensing pharmaceutical compounds and technology, conducting clinical trials, and raising capital. The Company’s lead program is vecabrutinib, formerly known as SNS-062, a non-covalent inhibitor of Bruton’s Tyrosine Kinase (“BTK”). Vecabrutinib is being studied in a Phase 1b/2 clinical trial in B-cell malignancies. In January 2017, the Company announced that its Investigational New Drug (“IND”) application with the U.S. Food and Drug Administration (“FDA”) for vecabrutinib had become effective. In July 2017, the Company announced the dosing of the first patient in a Phase 1b/2 study to assess the safety and activity of vecabrutinib in patients with advanced B-cell malignancies after two or more prior therapies, including ibrutinib or another covalent BTK inhibitor, and including patients with BTK C481 mutations. The Company is also developing SNS-510, a PDK1 inhibitor licensed from Millennium Pharmaceuticals, Inc., a wholly-owned subsidiary of Takeda Pharmaceutical Company Limited (“Takeda”). Sunesis acquired from Takeda global commercial rights to several potential first-in class, preclinical inhibitors of the novel target PDK1, including SNS-510. Sunesis is currently characterizing SNS-510 in preclinical pharmacology and toxicology studies with the goal of filing an IND in 2019. The Company is in a collaboration with Takeda for the development of TAK-580 (formerly MLN2480), an oral pan-RAF inhibitor, for which Takeda is conducting a multi-arm, open-label Phase 1b study in combination with various anticancer agents in adult patients with advanced solid tumor cancers. Liquidity and Going Concern The Company has incurred significant losses and negative cash flows from operations since its inception, and as of December 31, 2017, had cash, cash equivalents and marketable securities totaling $31.8 million and an accumulated deficit of $632.9 million. The Company expects to continue to incur significant losses for the foreseeable future as it continues development of its kinase inhibitor pipeline, including its BTK inhibitor vecabrutinib. Following the decision to withdraw the European Marketing Authorization Application (“MAA”) for vosaroxin, the Company has prioritized development funding on kinase inhibitors with a focus on vecabrutinib. The Company has a limited number of products that are still in the early stages of approval and will require significant additional investment. The Company’s cash, cash equivalents and marketable securities are not sufficient to support its operations for a period of twelve months from the date the financial statements are issued. These factors raise substantial doubt about its ability to continue as a going concern. The Company will require additional financing to fund working capital, repay debt and pay its obligations as they come due. Additional financing might include one or more offerings and one or more of a combination of equity securities, debt arrangements or partnership or licensing collaborations. However, there can be no assurance that the Company will be successful in acquiring additional funding at levels sufficient to fund its operations or on terms favorable to the Company. If the Company is unsuccessful in its efforts to raise additional financing in the near term, the Company will be required to significantly reduce or cease operations. The principal payments due under the Loan Agreement have been classified as a current liability as of December 31, 2017 due to the considerations discussed above and the assessment that the material adverse change clause under the Loan Agreement is not within the Company's control. The Company has not been notified of an event of default by the Lender as of the date of the filing of this Form 10-K. The accompanying financial statements have been prepared assuming the Company will continue to operate as a going concern, which contemplates the realization of assets and the settlement of liabilities in the normal course of business. The consolidated financial statements do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts of liabilities that may result from uncertainty related to the Company’s ability to continue as a going concern . Concentrations of Credit Risk In accordance with its investment policy, the Company invests cash that is not currently being used for operational purposes. The policy allows for the purchase of low risk debt securities issued by: (a) the United States and certain European governments and government agencies, and (b) highly rated banks and corporations, denominated in U.S. dollars, Euros, or British pounds, subject to certain concentration limits. The policy limits maturities of securities purchased to no longer than 24 months and the weighted average maturity of the portfolio to 12 months. Management believes these guidelines ensure both the safety and liquidity of any investment portfolio the Company may hold. Financial instruments that potentially subject the Company to concentrations of credit risk generally consist of cash, cash equivalents and marketable securities. The Company is exposed to credit risk in the event of default by the institutions holding its cash, cash equivalents and any marketable securities to the extent of the amounts recorded in the balance sheets.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued a new revenue recognition standard which amends revenue recognition principles and provides a single, comprehensive set of criteria for revenue recognition within and across all industries. The core principle of the guidance is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The guidance also requires improved disclosures on the nature, amount, timing, and uncertainty of revenue that is recognized. In August 2015, the FASB issued an update to the guidance to defer the effective date by one year, such that the new standard will be effective for annual reporting periods beginning after December 15, 2017 and interim periods therein. The standard allows for adoption using a full retrospective method or a modified retrospective method. The Company will apply the new guidance effective January 1, 2018 using the modified retrospective method to contracts that are not completed as of January 1, 2018. The Company’s revenues are derived from license arrangements. The consideration the Company is eligible to receive under the license arrangements includes upfront payments, milestone payments, and royalties. In the fourth quarter of 2017, the Company completed its assessment of the new guidance and the adoption of this guidance, including the cumulative effect of any adjustment to the opening balance of retained earnings, will not have a material impact to its consolidated financial statements. In January 2016, the FASB issued Accounting Standards Update (“ASU”) Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued ASU No. 2016-02, Leases In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Sunesis Europe Limited, a United Kingdom corporation, and Sunesis Pharmaceuticals (Bermuda) Ltd., a Bermuda corporation, as well as a Bermuda limited partnership, Sunesis Pharmaceuticals International LP. All intercompany balances and transactions have been eliminated in consolidation. Segment Reporting Management has determined that the Company operates as a single reportable segment. Significant Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the Company’s consolidated financial statements and accompanying notes thereto. Actual results could differ materially from these estimates. Estimates, assumptions and judgments made by management include those related to the valuation of equity and related instruments, revenue recognition, stock-based compensation and clinical trial accounting. Cash Equivalents and Marketable Securities The Company considers all highly liquid securities with original maturities of three months or less from the date of purchase to be cash equivalents, which generally consist of money market funds and corporate debt securities. Marketable securities consist of securities with original maturities of greater than three months, which may include U.S. and European government obligations and corporate debt securities. Management determines the appropriate classification of securities at the time of purchase income equity The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion is included in other income, net in the statements of operations and comprehensive loss. Realized gains and losses and declines in value judged to be other-than-temporary on available-for-sale securities, if any, are also recorded to other income, net. The cost of securities sold is based on the specific-identification method. Invoices for certain services provided to the Company are denominated in foreign currencies. To manage the risk of future movements in foreign exchange rates that would affect such amounts, the Company may purchase certain European currencies or highly-rated investments denominated in those currencies, subject to similar criteria as for other investments defined in the Company’s investment policy. There is no guarantee that the related gains and losses will substantially offset each other, and the Company may be subject to significant exchange gains or losses as currencies fluctuate from quarter to quarter. To date, the Company has purchased Euros and Euro-denominated obligations of foreign governments and corporate debt. As of December 31, 2017 and December 31, 2016, the Company held investments denominated in Euros with an aggregate fair value of $0.8 million and $0.7 million, respectively. Any cash, cash equivalent and short-term investment balances denominated in foreign currencies are recorded at their fair value based on the current exchange rate as of each balance sheet date. The resulting exchange gains or losses and those from amounts payable for services originally denominated in foreign currencies are both recorded in other income, net in the statements of operations and comprehensive loss. Fair Value Measurements The Company measures cash equivalents and marketable securities at fair value on a recurring basis using the following hierarchy to prioritize valuation inputs, in accordance with applicable GAAP: Level 1 - quoted prices (unadjusted) in active markets for identical assets and liabilities that can be accessed at the measurement date Level 2 - inputs other than quoted prices included within Level 1 that are observable, either directly or indirectly Level 3 - unobservable inputs The Company’s Level 2 valuations of marketable securities are generally derived from independent pricing services based upon quoted prices in active markets for similar securities, with prices adjusted for yield and number of days to maturity, or based on industry models using data inputs, such as interest rates and prices that can be directly observed or corroborated in active markets. The carrying amounts of the Company’s financial instruments, including Property and Equipment Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is determined using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized on a straight-line basis over the shorter of their estimated useful lives or the term of the lease. Accounting for Royalty Agreement The payment of $25.0 million by RPI under the Royalty Agreement (see Note 6) is non-refundable, and no revenue participation right payments will be made unless vosaroxin is T , less $3.1 million initially . The fair value of the warrants was recorded to additional paid-in capital. Accounting for Notes Payable The accounting for certain fees and expenses related to the Loan Agreement (see Note 8) is as follows. The facility fee is being accounted for as a debt discount and classified within notes payable on the Company’s balance sheet. The fair value of the warrants issued in connection with the Loan Agreement have been recorded as a debt discount within notes payable and an increase to additional paid-in capital on the Company’s balance sheet. The debt discount is being amortized as interest expense over the term of the loan using the effective interest method. The final payment is being accreted as interest expense over the term of the loans using the effective interest method. The legal fees are being accounted for as deferred debt issuance costs within assets on the Company’s balance sheet and are being amortized as other income, net over the term of the loans using the effective interest method. Revenue Recognition Revenue arrangements with multiple deliverables are accounted for in accordance with the Financial Accounting Standards Board Accounting Standards Codification, Subtopic 605-25, Multiple-Element Arrangements Non-refundable fees where the Company has no continuing performance obligations are recognized as revenues when collection is reasonably assured. In situations where continuing performance obligations exist, non-refundable fees are deferred and recognized ratably over the projected performance period. Milestone payments from license or collaboration agreements which are substantive and at risk at the time the agreement is executed are recognized upon completion of the applicable milestone event. Royalty revenues, if any, will be recognized based on reported product sales by third-party licensees. Research funding from any future agreement will be recognized as the related research services are performed. Research and Development Research and development expense consists primarily of: (a) clinical trial costs, which include payments for work performed by contract research organizations (“CROs”), clinical trial sites, labs and other clinical service providers, and for drug packaging, storage and distribution; (b) drug manufacturing costs, which include costs for producing drug substance and drug product, and for stability and other testing; (c) personnel costs for related permanent and temporary employees; (d) other outside services and consulting costs; and (e) payments under license agreements. All research and development costs are expensed as they are incurred. Clinical Trial Accounting The Company records accruals for estimated clinical trial costs, which include payments for work performed by CROs and participating clinical trial sites. These costs are generally a significant component of research and development expense. Costs incurred for setting up clinical trial sites for participation in trials are generally non-refundable, and are expensed as incurred, with any refundable advances related to enrollment of the first patient recorded as prepayments and assessed for recoverability on a quarterly basis. Costs related to patient enrollment are accrued as patients progress through the clinical trial, including amortization of any first-patient prepayments. This amortization generally matches when the related services are rendered, however, these cost estimates may or may not match the actual costs incurred by the CROs or clinical trial sites, and if the Company has incomplete or inaccurate information, the clinical trial accruals may not be accurate. The difference between accrued expenses based on the Company’s estimates and actual expenses have not been significant to date. Stock-Based Compensation The Company grants options to purchase common stock to its employees, directors and consultants under its stock option plans. Under the Company’s Employee Stock Purchase Plan, eligible employees can also purchase shares of the Company’s common stock at 85% of the lower of the fair market value of the Company’s common stock at the beginning of a 12-month offering period or at the end of one of the two related six-month purchase periods. The Company values these share-based awards using the Black-Scholes option valuation model (the “Black-Scholes model”). The determination of fair value of share-based payment awards on the date of grant using the Black-Scholes model is affected by the Company’s stock price as well as assumptions regarding a number of highly complex and subjective variables. These variables include, but are not limited to, the expected stock price volatility over the term of the awards and actual and projected employee stock option exercise behaviors. Foreign Currency Transactions that are denominated in a foreign currency are translated into U.S. dollars at the current exchange rate on the transaction date. Any foreign currency-denominated monetary assets and liabilities are subsequently remeasured at current exchange rates as of each balance sheet date, with gains or losses on foreign exchange recognized in other income, net in the statements of operations and comprehensive loss. Income Taxes The Company accounts for income taxes under the liability method. Under this method, deferred tax assets and liabilities are determined based on the differences between the tax basis of assets and liabilities and their basis for financial reporting. Deferred tax assets or liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which temporary differences are expected to be recovered or settled. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company’s policy is to recognize interest charges and penalties in other income, net in the statements of operations and comprehensive loss.

Loss per Common Share

Loss per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Loss per Common Share	3. Loss per Common Share Basic loss per common share is calculated by dividing net loss by the weighted-average number of common shares outstanding for the period. Diluted net loss per common share is computed by dividing (a) net loss, less any anti-dilutive amounts recorded during the period, by (b) the weighted-average number of common shares outstanding for the period plus dilutive potential common shares as determined using the treasury stock method for options and warrants to purchase common stock. The following table sets forth the computation of basic and diluted loss per common share for the periods presented (in thousands, except per share amounts): Year Ended December 31, 2017 2016 2015 Numerator: Net loss—basic $ (35,458 ) $ (38,023 ) $ (36,676 ) Net loss—diluted $ (35,458 ) $ (38,023 ) $ (36,676 ) Denominator: Weighted-average common shares outstanding—basic 24,516 15,688 12,156 Weighted-average common shares outstanding—diluted 24,516 15,688 12,156 Net loss per common share: Basic $ (1.45 ) $ (2.42 ) $ (3.02 ) Diluted $ (1.45 ) $ (2.42 ) $ (3.02 ) The following table represents the potential common shares issuable pursuant to outstanding securities as of the related period end dates that were excluded from the computation of diluted loss per common share because their inclusion would have had an anti-dilutive effect (in thousands): As of December 31, 2017 2016 2015 Warrants to purchase shares of common stock 5,218 218 938 Convertible preferred stock 6,331 4,270 3,353 Options to purchase shares of common stock 3,532 2,697 2,153 Outstanding securities not included in calculations 15,081 7,185 6,444

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Financial Instruments	4. Financial Instruments Financial Assets The following tables summarize the estimated fair value of the Company’s financial assets measured on a recurring basis as of the dates indicated, which were comprised solely of available-for-sale marketable securities with remaining contractual maturities of one year or less (in thousands): Gross Gross Valuation Amortized Unrealized Unrealized Estimated Fair December 31, 2017 Input Level Cost Gains Losses Value Money market funds Level 1 $ 20,470 $ — $ — $ 20,470 U.S. corporate debt obligations Level 2 3,282 — (5 ) 3,277 U.S. commercial paper Level 2 1,498 — (2 ) 1,496 Total available-for-sale securities 25,250 — (7 ) 25,243 Less amounts classified as cash equivalents (20,470 ) — — (20,470 ) Amounts classified as marketable securities $ 4,780 $ — $ (7 ) $ 4,773 Gross Gross Valuation Amortized Unrealized Unrealized Estimated Fair December 31, 2016 Input Level Cost Gains Losses Value Money market funds Level 1 $ 3,270 $ — $ — $ 3,270 U.S. treasury securities Level 1 16,029 $ — $ (9 ) 16,020 U.S. certificates of deposit Level 1 4,868 $ — $ — 4,868 U.S. corporate debt obligations Level 2 11,617 — (11 ) 11,606 U.S. commercial paper Level 2 2,521 — (2 ) 2,519 Total available-for-sale securities 38,305 — (22 ) 38,283 Less amounts classified as cash equivalents (3,751 ) — — (3,751 ) Amounts classified as marketable securities $ 34,554 $ — $ (22 ) $ 34,532 The following table summarizes the available-for-sale securities that were in an unrealized loss position as of December 31, 2017, each Gross Unrealized Estimated Fair December 31, 2017 Losses Value U.S. corporate debt obligations (5 ) 3,277 U.S. commercial paper (2 ) 1,496 Total available-for-sale securities in an unrealized loss position $ (7 ) $ 4,773 No significant facts or circumstances have arisen to indicate that there has been any deterioration in the creditworthiness of the issuers of these securities. The gross unrealized losses are not considered to be significant and have generally been for relatively short durations. The Company does not intend to sell these securities before maturity and it is not likely that they will need to be sold prior to the recovery of their amortized cost basis. There were no sales of available-for-sale debt securities in the years ended December 31, 2017, 2016 2015

Other Accrued Liabilities

Other Accrued Liabilities	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Other Accrued Liabilities	5. Other Accrued Liabilities Other accrued liabilities as of December 31 were as follows (in thousands): 2017 2016 Accrued outside services $ 1,096 $ 1,192 Accrued professional services 471 381 Other accruals 3 118 Total other accrued liabilities $ 1,570 $ 1,691

Royalty Agreement

Royalty Agreement	12 Months Ended
	Dec. 31, 2017
Revenue Recognition [Abstract]
Royalty Agreement	6. Royalty Agreement In March 2012, the Company entered into a Revenue Participation Agreement (the “Royalty Agreement”), with RPI Finance Trust (“RPI”), an entity related to Royalty Pharma. In September 2012, pursuant to the provisions of the Royalty Agreement, RPI made a $25.0 million cash payment to the Company. The payment, less $3.1 million representing the fair value of the warrants granted under the arrangement, was initially classified as deferred revenue and amortized to revenue over the related performance period. Based on the regulatory interactions with the FDA and EMA outlined in Note 1, the Company extended the end date of the estimated performance period through which the balance of deferred revenue was be amortized from September 30, 2016 to March 31, 2017. As a result, the quarterly amortization was adjusted from $0.9 million per quarter to $0.6 million per quarter, commencing with the quarter ended September 30, 2015. Revenue participation right payments will be made to RPI when and if vosaroxin is commercialized, at a rate of 6.75% of net sales of vosaroxin, on a product-by-product and country-by-country basis world-wide through the later of: (a) the expiration of the last to expire of certain specifically identified patents; (b) 10 years from the date of first commercial sale of such product in such country; or (c) the expiration of all applicable periods of data, market or other regulatory exclusivity in such country with respect to such product.

License Agreements

License Agreements	12 Months Ended
	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
License Agreements	7. License Agreements Overview In August 2004, the Company entered into a collaboration agreement with Biogen MA, Inc. (“Biogen”) to discover, develop and commercialize small molecule inhibitors of the human protein Raf kinase, including family members Raf-1, A-Raf, B-Raf and C-Raf (collectively “Raf”) and up to five additional targets that play a role in oncology and immunology indications (the “Biogen OCA”). In connection with the Company’s June 2008 restructuring, the parties agreed to terminate the research obligations and related funding as of June 30, 2008. In March 2011, as part of a series of agreements among the Company, Biogen and Millennium Pharmaceuticals, Inc., a wholly-owned subsidiary of Takeda Pharmaceutical Company Limited, (“Takeda”), the Company entered into: (a) an amended and restated collaboration agreement with Biogen (the “Biogen 1st ARCA”); (b) a license agreement with Takeda (the “Takeda Agreement”); and (c) a termination and transition agreement among the Company, Biogen and Takeda (the “Termination and Transition Agreement”). The Termination and Transition Agreement provided for (a) the termination of Biogen’s exclusive rights under the Biogen OCA to all discovery programs under such agreement other than for small molecule inhibitors of the human protein Bruton’s tyrosine kinase (“BTK”); (b) the permitted assignment to Takeda of all related Company collaboration assets and rights to Raf kinase and the human protein phosphoinositide-dependent kinase-1 (“PDK1”); and (c) the payment of $4.0 million upfront from Takeda to the Company, which was recorded as revenue in March 2011. Biogen Idec The Biogen 1st ARCA amended and restated the Biogen OCA, to provide for the discovery, development and commercialization of small molecule BTK inhibitors. Under this agreement, the Company no longer has research obligations, but licenses granted to Biogen with respect to the research collaboration under the Biogen OCA (other than the licenses transferred to Takeda under the Takeda Agreement) remain in effect. In June 2012, the Company received an event-based payment and recognized as revenue of $1.5 million from Biogen for the advancement of pre-clinical work in connection with the Biogen 1st ARCA. Under this agreement, the Company is eligible to receive up to an additional $58.5 million in pre-commercialization event-based payments related to the development by Biogen of the first two indications for licensed products against the BTK target. The Company is also eligible to receive royalty payments depending on related product sales, if any. In December 2013, the Company entered into a second amended and restated collaboration agreement with Biogen (the “Biogen 2nd ARCA”), to provide the Company with an exclusive worldwide license to develop, manufacture and commercialize vecabrutinib vecabrutinib vecabrutinib Takeda Under the Takeda Agreement, the Company granted exclusive licenses to products against two oncology targets originally developed under the Biogen OCA, Raf and PDK1, under substantially the same terms as under the Biogen OCA. In January 2014, the Company entered into an amended and restated license agreement with Takeda (the “Amended Takeda Agreement”), to provide the Company with an exclusive worldwide license to develop and commercialize preclinical inhibitors of PDK1. In connection with the With respect to the Raf target product rights that were originally licensed to Takeda under the Takeda Agreement, the Company may in the future receive up to $57.5 million in pre-commercialization event-based payments related to the development by Takeda of the first two indications for each of the licensed products directed against the Raf target and royalty payments depending on related product sales. Takeda is currently conducting a Phase 1b clinical study of an oral investigative drug, TAK-580, which is licensed to them under the Amended Takeda Agreement.

Notes Payable

Notes Payable	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Notes Payable	8. Notes Payable On March 31, 2016, the Company entered into a loan and security agreement (the “Loan Agreement”) with On June 30, 2017, the Company entered into an amendment to the existing Loan Agreement (the “Amended Loan Agreement”). Under terms of the Amended Loan Agreement, the Company will be required to pay interest on the borrowings under the Loan Agreement at a per annum rate equal to 8.54% plus the then effective one-month U.S. LIBOR rate. The Amendment modified the loan repayment terms to be interest-only through July 1, 2018, followed by twenty-two (22) equal monthly payments of principal and interest through the maturity date, contingent upon receipt of at least Fifteen Million Dollars ($15,000,000) in unrestricted cash proceeds received after June 1, 2017 from the issuance by the Company of new equity securities any time after June 1, 2017 through December 31, 2017. Thereafter and until the scheduled maturity date of April 1, 2020, in addition to interest accrued during such period, the monthly payments will include an amount equal to the outstanding principal divided by 28 months, unless the interest only period is extended by a further six months, in which case the amortization period will be 22 months. In addition to principal and interest, a final payment equal to $312,500 will be due upon maturity or such earlier date specified in the Loan Agreement. If the Company repays all amounts owed under the Loan Agreement prior to the maturity date, the Company will pay a prepayment fee equal 1.0% of the amount prepaid if the prepayment occurs after June 30, 2017 through March 31, 2018 and 0.5% of the amount prepaid if the prepayment occurs thereafter. On October 31, 2017, the Company entered into a second amendment to the Amended Loan Agreement (the “Second Amendment”). The Second amendment modified the loan repayment terms to add two additional extended interest-only periods beyond July 1, 2018. If under the terms of the Amended Loan Agreement, the interest-only period has been extended to July 1, 2018, the Company may further extend the interest-only period to October 1, 2018, contingent upon the receipt of at least Fifteen Million dollars ($15,000,000) in unrestricted net cash proceeds from the issuance by the Company of new equity securities or as a non-refundable upfront payment on a new business development agreement or royalty financing agreement (the “New Capital”), on or after October 24, 2017, but on or prior to December 31, 2017. Subsequently, the Company may further extend the interest-only period to January 1, 2019, contingent upon the receipt of at least Twenty-Five Million dollars ($25,000,000) in New Capital (inclusive of any prior amounts received after October 24, 2017), on or after October 24, 2017, but on or prior to September 15, 2018. The facility fee and legal fees related to the debt are being accounted for as a debt discount and classified In conjunction with the Loan Agreement, the Lenders were issued five-year warrants to purchase an Pursuant to the Loan Agreement and the amendments, the Company is bound by a variety of affirmative covenants during the term of the Loan Agreement, including, without limitation, certain information delivery requirements, notice requirements and obligations to maintain certain insurance. Additionally, the Company is bound by certain negative covenants setting forth actions that are not permitted to be taken during the term of the Amended Loan Agreement without the Lenders’ consent, including, without limitation, incurring certain additional indebtedness, making certain asset dispositions, entering into certain mergers, acquisitions or other business combination transactions or incurring any non-permitted lien or other encumbrance on the Company’s assets. Upon the occurrence of an event of default under the Amended Loan Agreement (subject to cure periods for certain events of default), all amounts owed by the Company thereunder would begin to bear interest at a rate that is 5.0% higher than the rate that would otherwise be applicable and may be declared immediately due and payable by the Collateral Agent. Events of default under the Amended Loan Agreement include, among other things, the following: the occurrence of certain bankruptcy events; the failure to make payments under the Loan Agreement when due; the occurrence of a material impairment on the Collateral Agent’s security interest over the collateral, a material adverse change in the business, operations or condition (financial or otherwise) of the Company or material impairment of the prospect of repayment of the obligations under the Amended Loan Agreement; the occurrence of a default under certain other agreements entered into by the Company; the rendering of certain types of judgments against the Company; the revocation of certain government approvals of the Company; any breach by the Company of any covenant (subject to cure periods for certain covenants) made in the Amended Loan Agreement; and the failure of any representation or warranty made by the Company in connection with the Amended Loan Agreement to be correct in all material respects when made. The Amended Loan Agreement defines certain events of default, including instances of a Material Adverse Change in its operations, which may require prepayment of the outstanding loan. In the event of default by the Company under the Loan Agreement, the Lenders would be entitled to exercise their remedies thereunder, including the right to accelerate the debt, upon which the Company may be required to repay all amounts then outstanding under the Loan Agreement, which could harm the Company's financial condition. The Company was in compliance with all applicable covenants set forth in the Loan Agreement as of December 31, 2017 and 2016. The Collateral Agent, for the benefit of the Lenders, has a perfected security interest in substantially all of the Company’s property, rights and assets, except for intellectual property, to secure the payment of all amounts owed to the Lenders under the Loan Agreement. Aggregate future minimum payments due under the Loan Facility as of December 31, 2017 Year ending December 31, Total 2018 1,586 2019 5,442 2020 2,014 Total minimum payments 9,042 Less amount representing interest (1,542 ) Total notes payable as of December 31, 2017 7,500 Less unamortized debt discount and issuance costs (296 ) Less current portion of notes payable (7,204 ) Non-current portion of notes payable $ —

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Commitments The Company’s operating lease obligation s solely ing In January 2014, a lease for 15,378 square feet was entered into with an expiry date of April 30, 2015. In June 2014, the lease was amended to extend the expiration date to June 30, 2015, and to add 6,105 square feet of additional office space within the same building. The lease has been amended in January 2015 and September 2015 to extend the expiration date to December 31, 2016 Aggregate non-cancelable future minimum rental payments under operating leases as of December 31, 2017, were as follows (in thousands): Year Ending December 31, Payments 2018 $ 514 2019 $ 562 2020 $ 579 2021 $ 294 Total rental payments $ 1,949 The Company recognizes rent expense on a straight-line basis. The Company recorded rent expense of $0.7 million, $0.6 Contingencies From time to time, the Company may be involved in legal proceedings, as well as demands, claims and threatened litigation, which arise in the normal course of its business or otherwise. The ultimate outcome of any litigation is uncertain and unfavorable outcomes could have a negative impact on the Company’s results of operations and financial condition. Regardless of outcome, litigation can have an adverse impact on the Company because of the defense costs, diversion of management resources and other factors. The Company is not currently involved in any material legal proceedings.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	10. Stockholders’ Equity Preferred Stock The Company has 10,000,000 shares of authorized preferred stock available for issuance in one or more series. Upon issuance, the Company can determine the rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of such series, any or all of which may be greater than the rights of common stock. There were 17,697 shares and 17,897 shares of preferred stock outstanding as of December 31, 2017 2016, respectively. These shares are non-voting Series B, Series C, and Series D Convertible Preferred Stock at a price of $840, $3,850, and $2,000 per share, respectively. Each share of non-voting Series B is convertible into 166 shares of common stock and each share of non-voting Series C Stock and Series D Stock is convertible into 1000 shares of common stock, provided that conversion will be prohibited if, as a result, the holder and its affiliates would own more than 9.98% of the total number of shares of common stock then outstanding • senior to all of the Company’s Common Stock; • senior to any class or series of the Company’s capital stock hereafter created specifically ranking by its terms junior to the Series B, Series C, and Series D Stock; • on parity with any class or series of the Company’s capital stock hereafter created specifically ranking by its terms on parity with the Series B, Series C, and Series D Stock; • junior to any class or series of the Company’s capital stock hereafter created specifically ranking by its terms senior to the Series B, Series C, and Series D Stock; in each case, as to distributions of assets upon the Company’s liquidation, dissolution or winding up whether voluntarily or involuntarily. Common Stock Holders of common stock are entitled to one vote per share on all matters to be voted upon by the stockholders of the Company. Subject to the preferences that may be applicable to any outstanding shares of preferred stock, the holders of common stock are entitled to receive ratably such dividends, if any, as may be declared by the Board of Directors. Under the terms of the Loan Agreement with the Lenders, the Company is precluded from paying cash dividends without the prior written consent of the Lenders. Underwritten Offerings In December 2015, the Company completed underwritten offering of (i) 1,832,698 shares of its common stock, that included the In October 2016, the Company completed underwritten offering of (i) 5,675,825 shares of its common stock at a price of $3.85 per share, and (ii) 1,558 shares of its non-voting Series C Convertible Preferred Stock (“Series C Stock”) at a price of $3,850.00 per share. Gross proceeds from the sale were $27.9 million and net proceeds were $25.9 million. Each share of non-voting Series C Stock is convertible into 1,000 shares of Sunesis common stock, provided that conversion will be prohibited if, as a result, the holder and its affiliates would own more than 9.98% of the total number of shares of Sunesis common stock then outstanding. In October 2017, the Company completed underwritten offerings of (i) 7,500,000 shares of its common stock and accompanying warrants to purchase 3,750,000 shares of its common stock at a price to the public of $2.00 for each share of common stock and warrant to purchase 0.5 shares of common stock, and (ii) 2,500 shares of its non-voting Series D Convertible Preferred Stock (“Series D Stock”) and accompanying warrants to purchase 1,250,000 shares of its common stock at a price to the public of $2,000 for each share of Series D Stock and warrant to purchase 500 shares of common stock. The exercise price of the warrants is $3.00 per whole share of common stock. Each share of non-voting Series D Stock is convertible into 1,000 shares of its common stock, provided that conversion will be prohibited if, as a result, the holder and its affiliates would own more than 9.98% of the total number of shares of its common stock then outstanding. Gross proceeds from the sale were $20.0 million and net proceeds were $18.5 million. Controlled Equity Offerings In August 2011, the Company entered into a Controlled Equity Offering SM During the year ended December 31, 2017, the Company sold an aggregate of 5,321,151 2.72 14.2 45.0 Equity Incentive Plans The Company grants options to purchase shares of its common stock primarily to: (i) new employees, of which 25% of the shares subject to such options become exercisable on the first anniversary of the vesting commencement date, and 1/48th of the shares subject to such options become exercisable each month over the remainder of the four-year vesting period, (ii) existing employees with various vesting schedules over three to four years, (iii) new non-employee members of the board of directors, of which 50% of the shares subject to such options become exercisable on each of the first and second anniversary of the vesting commencement date, and (iv) continuing non-employee members of the board of directors, of which 1/24th of the shares subject to such options become exercisable each month following the date of grant over a two-year vesting period. On March 15, 2011, the Company’s Board of Directors adopted, and on June 3, 2011, the Company’s stockholders approved, the 2011 Equity Incentive Plan (the “2011 Plan”). The 2011 Plan is intended as the successor to and continuation of the Company’s 1998 Stock Plan, 2001 Stock Plan, 2005 Equity Incentive Award Plan and 2006 Employment Commencement Incentive Plan (collectively, the “Prior Plans”). No additional stock awards will be granted under the Prior Plans. The Company initially reserved a total of 1,006,976 shares of common stock for issuance under the 2011 Plan, which is the sum of (i) the 89,967 shares remaining available as of the Effective Date under the Prior Plans, (ii) an additional 733,333 new shares, and (iii) that portion of the 183,676 shares underlying stock options granted and currently outstanding under the Prior Plans that expire or terminate for any reason prior to exercise or settlement or that are forfeited because of the failure to meet a contingency or condition required to vest such shares. The number of shares of common stock available for issuance under the 2011 Plan automatically increases on January 1st of each year for a period of 10 years commencing on January 1, 2012 by an amount equal to: (i) 4.0% of the Company’s outstanding shares of common stock on December 31st of the preceding calendar year, or (ii) a lesser amount determined by the Board of Directors. On January 1, 2017 and 2016, in accordance with the above, . During the year ended December 31, 2017, options to purchase 2,105,293 82,585 Employee Stock Purchase Plans On March 5, 2011, the Company’s Board of Directors adopted, and on June 3, 2011, the Company’s stockholders approved, the 2011 Employee Stock Purchase Plan (the “2011 ESPP”). The 2011 ESPP permits eligible employees to purchase common stock at a discount through payroll deductions during defined offering periods. Eligible employees can purchase shares of the Company’s common stock at 85% of the lower of the fair market value of the common stock at (i) the beginning of a 12-month offering period, or (ii) at the end of one of the two related 6-month purchase periods. No participant in the 2011 ESPP may be issued or transferred shares of common stock valued at more than $25,000 per calendar year. The Company initially reserved a total of 83,333 shares of common stock for issuance under the 2011 ESPP. The number of shares of common stock available for issuance under the 2011 ESPP automatically increases on January 1st of each year for a period of 10 years commencing on January 1, 2012 by an amount equal to: (i) 1.0% of the Company’s outstanding shares of common stock on December 31st of the preceding calendar year, or (ii) a lesser amount determined by the Board of Directors. A total of 87,020 Warrants Warrants to purchase shares of the Company’s common stock outstanding as of December 31, 2017 were as follows (in thousands, except per share amounts): Exercise Price Date Issued Shares Per Share Expiration February 2015 10 $ 13.32 February 2020 March 2016 208 $ 3.25 March 2021 October 2017 5,000 $ 3.00 October 2018 Total warrants outstanding and exercisable 5,218 Reserved Shares Shares of the Company’s common stock reserved for future issuance as of December 31, 2017 Shares Available Total for Future Outstanding Shares Grant Securities Reserved Warrants — 5,218 5,218 Convertible preferred stock — 6,331 6,331 Stock option plans 83 3,532 3,615 Employee stock purchase plan 168 — 168 Total reserved shares of common stock 251 15,081 15,332

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	11. Stock-Based Compensation Overview Employee stock-based compensation expense is calculated based on the grant-date fair value of awards ultimately expected to vest and recognized under the straight-line attribution method, assuming that all stock-based awards will vest. The following table summarizes stock-based compensation expense related to the Company’s stock-based awards for the periods indicated (in thousands): Year ended December 31, 2017 2016 2015 Research and development $ 865 $ 1,630 $ 2,856 General and administrative 2,059 2,970 3,292 Employee stock-based compensation expense 2,924 4,600 6,148 Non-employee stock-based compensation expense 109 191 196 Total stock-based compensation expense $ 3,033 $ 4,791 $ 6,344 Option Exchange Program On June 9, 2017, we filed a Tender Offer Statement (TO) on Schedule TO relating to an option exchange program for its officers and employees (the Option Exchange) to exchange certain stock options to purchase up to an aggregate of 781,505 shares of its common stock that had been granted to eligible holders, for a lesser number of new stock options with a lower exercise price. Stock options with an exercise price greater than or equal to $8.00, and held by eligible holders in continuous service through the termination of the Option Exchange, were eligible for exchange in the program. An exchange ratio of 1.30 for 1 was applied to options priced from $8.00 to $19.99, and an exchange ratio of 1.75 for 1 was applied to options priced at $20.00 or greater. As of the closing of the Option Exchange on July 10, 2017, 25 eligible holders had tendered an aggregate of 778,928 options for 543,650 new options to purchase shares of its common stock. Each new stock option was granted on July 10, 2017, pursuant to its 2011 Equity Incentive Plan with an exercise price per share of $2.62, which was the closing market price on the grant date of the new options. The exchange of stock options was treated as a modification for accounting purposes and resulted in an incremental expense of $50,957, for the vested options, which was calculated using the Black-Scholes option pricing model. The incremental expense together with the unamortized expense remaining on the unvested options is being amortized over the vesting period of the new options. Fair Value of Awards The Company determines the fair value of stock-based awards on the grant date using the Black-Scholes model, which is impacted by the Company’s stock price, as well as assumptions regarding a number of highly subjective variables. The following table summarizes the weighted-average assumptions used as inputs to the Black-Scholes model, and resulting weighted-average and total estimated grant date fair values of employee stock options granted during the periods indicated: Year Ended December 31, 2017 2016 2015 Assumptions: Expected term (years) 4.8 5.3 5.2 Expected volatility 112.5 % 110.0 % 99.9 % Risk-free interest rate 2.1 % 1.9 % 1.7 % Expected dividend yield 0.0 % 0.0 % 0.0 % Fair value: Weighted-average estimated grant date fair value per share $ 2.68 $ 3.12 $ 6.20 Options granted to employees (in thousands) 1,280 750 531 Total estimated grant date fair value (in thousands) $ 3,434 $ 2,344 $ 3,294 The estimated fair value of stock options that vested in the years ended December 31, 2017, 2016 and 2015, was $ 1.9 4.6 5.8 Option Plan Activity The following table summarizes stock option activity for the Company’s stock option plans in the periods presented (in thousands, except per share amounts): Weighted Weighted Average Average Number Exercise Remaining Aggregate of Price Per Contractual Intrinsic Shares Share Term (Years) Value Outstanding as of December 31, 2016 2,641 $ 13.50 Options granted 2,105 $ 3.19 Options exercised (8 ) $ 3.00 Options forfeited or expired (1,206 ) $ 17.00 Outstanding as of December 31, 2017 3,532 $ 6.18 7.19 $ 1,064 Vested and expected to vest as of December 31, 2017 3,532 $ 6.18 7.19 $ 1,064 Exercisable as of December 31, 2017 1,327 $ 10.74 4.13 $ 246 The aggregate intrinsic value in the table above represents the total pre-tax intrinsic value (i.e., the difference between the Company’s closing stock price on the last trading day of the period and the exercise price, multiplied by the number of in-the-money options) that would have been received by option holders if they had exercised all their options on December 31, 2017. The intrinsic value of options exercised during the years ended December 31, 2017, 2016 2015 0.1 million, and Total estimated unrecognized stock-based compensation cost related to unvested stock options was $ 4.1 2.7 Bonus Awards On February 11, 2016, the Compensation Committee of the Company’s Board of Directors approved cash bonuses to certain of the Company’s employees, including its named executive officers, pursuant to the Company’s 2015 Bonus Program. Under the 2015 Bonus Program, each participant was eligible to receive a cash bonus in an amount up to a specified target percentage of such participant’s annual base salary for 2015 based on the level of achievement of certain corporate and individual objectives. The bonus payment amounts approved by the Compensation Committee were based on its determination of the degree to which such corporate and individual objectives were achieved. A portion of the bonuses awarded consisted of 122,000 fully vested shares of the Company’s common stock granted under the 2011 Plan. The stock portion of the bonus awards were granted effective as of February 29, 2016 and the cash portion of the bonus awards were paid on February 29, 2016. The number of shares of the Company’s common stock awarded to Mr. Daniel N. Swisher, Jr., the Company’s former CEO and President, and Mr. Eric H. Bjerkholt, the Company’s former Executive Vice President, Corporate Development and Finance, Chief Financial Officer and Corporate Secretary, under the 2011 Plan were determined based on the closing price of the Company’s common stock as quoted on the NASDAQ Capital Market on February 29, 2016, rounded down to the nearest whole share. Performance Awards On February 25, 2015, the Compensation Committee of the Board approved equity awards in the form of restricted stock units (“RSUs”) for certain of the Company’s employees (“participant”) under 2011 Stock Incentive Plan. The RSUs have an exercise price of $0 and vesting is subject to the achievement of the earlier of one of two milestones: acceptance of NDA (U.S.) or approval of MAA (EU) and the participant being an employee at time of milestone achievement. In May 2017, the RSUs were cancelled following the Company’s decision to withdraw the European MAA for vosaroxin as a treatment for relapsed/refractory AML in patients aged 60 years or older. The following table summarizes the Company's RSU activity for the year ended December 31, 2017 (in thousands, except per share amounts): Number of Performance based restricted stock units Shares Outstanding as of December 31, 2016 56 Stocks granted — Stocks exercised — Stocks cancelled (56 ) Outstanding as of December 31, 2017 —

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes Loss before the provision for income taxes consisted of the following (in thousands): Year Ended December 31, 2017 2016 2015 U.S. operations $ (24,776 ) $ (26,942 ) $ (23,705 ) Foreign operations (10,682 ) (11,081 ) (12,971 ) Loss before provision for income taxes $ (35,458 ) $ (38,023 ) $ (36,676 ) No provision for income taxes was recorded in the periods presented due to tax losses incurred in each period. The income tax provision differs from the amount computed by applying the statutory income tax rate of 34% to pre-tax loss as follows (in thousands): Year Ended December 31, 2017 2016 2015 Tax (benefit) at statutory federal rate 34.0 % 34.0 % 34.0 % State tax (benefit), net of federal benefit 1.2 0.6 (1.6 ) Foreign tax rate differential (10.2 ) (9.9 ) (12.0 ) Permanent differences (1.0 ) (3.2 ) 2.9 Research and development credits 0.7 1.0 (0.8 ) Change in valuation allowance 127.2 (22.5 ) (22.5 ) Change in tax rate (151.6 ) - - Other (0.3 ) - - Effective tax rate - % - % - % Deferred income taxes reflect the net tax effects of loss and credit carry-forwards and temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets for federal and state income taxes are as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Federal and state net operating loss carry-forwards $ 109,714 $ 156,066 Federal and state research credit carry-forwards 14,520 13,177 Capitalized research costs 6,304 4,824 Deferred revenue — 244 Stock-based compensation 4,528 5,739 Property and equipment 83 120 Accrued liabilities 117 207 Gross deferred tax assets 135,266 180,377 Valuation allowance (135,266 ) (180,377 ) Net deferred tax assets $ — $ — The Company’s unrecognized tax benefits relate to research and development tax credits claimed on the Company’s tax returns. The research and development tax credits have not been utilized, are fully offset by a valuation allowance, and currently have no tax expense impact. A reconciliation of the Company’s beginning and ending amount of unrecognized tax benefits is follows (in thousands): December 31, 2017 2016 Unrecognized tax benefits at beginning of period $ 1,441 $ 1,381 Increases related to current year tax positions 57 60 Increase related to change in tax rate 271 — Unrecognized tax benefits at the end of period $ 1,769 $ 1,441 Realization of the deferred tax assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance. The net valuation allowance decreased by approximately $45.1 million during the year ended December 31, 2017, and increased by approximately $8 .5 8.4 2015 As of December 31, 2017, the Company had federal net operating loss carry-forwards of $ 432.9 8.5 269.0 .4 Utilization of these net operating loss and tax credits carry-forwards may be subject to a substantial annual limitation due to the ownership change rules under Section 382 of the Internal Revenue Code of 1986, as amended (the “Code”). The limitations are applicable if an “ownership change,” as defined in the Code, is deemed to have occurred or occurs in the future. The annual limitation may result in the expiration of net operating loss and credit carry-forwards before they can be utilized. The Company recognizes the financial statement effect of tax positions when it is more likely than not that the tax positions will be sustained upon examination by the appropriate taxing authorities. As of December 31, 2017, 2016 and 2015, the Company had unrecognized tax benefits of $1.8 million, $1.4 million, and $1.4 million, respectively. On December 22, 2017, the 2017 Tax Cuts and Jobs Act (the Act") was enacted into law and the new legislation reduces the corporate tax rate to 21 percent, effectively January 1, 2018. Consequently, the Company remeasured the deferred tax assets and recorded a decrease in deferred tax assets and valuation allowance of $53.7 million. The Company believes that the one-time transition tax does not apply because there were no post-1986 earnings and profits (E&P) previously deferred from US income taxes. The Company had reviewed the effects of global intangible low-taxed income (“GILTI”) tax rules and does not expect any significant impact to its deferred tax assets. In accordance with SAB 118, the income tax effects from the Act are considered provisional and will be finalized before December 22, 2018. The Company files U.S. federal and California tax returns. The Company’s wholly owned subsidiaries, Sunesis Europe Limited and Sunesis Pharmaceuticals (Bermuda) Ltd., are currently not required to file tax returns. To date, neither the Company nor any of its subsidiaries have been audited by the Internal Revenue Service, any state income tax authority or tax authority in the related jurisdictions. Due to net operating loss carry-forwards, substantially all of the Company’s tax years remain open to federal tax examination.

Guarantees and Indemnification

Guarantees and Indemnification	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Guarantees and Indemnification	13. Guarantees and Indemnification As permitted under Delaware law and in accordance with the Company’s Bylaws, the Company indemnifies its officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the Company’s request in such capacity. The indemnification agreements with the Company’s officers and directors terminate upon termination of their employment, but the termination does not affect claims for indemnification relating to events occurring prior to the effective date of termination. The maximum amount of potential future indemnification is unlimited; however, the Company’s officer and director insurance policy reduces the Company’s exposure and may enable the Company to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification agreements is minimal. In addition, in the ordinary course of business the Company enters into agreements, such as licensing agreements, clinical trial agreements and certain services agreements, containing standard indemnifications provisions. The Company believes that the likelihood of an adverse judgment related to such indemnification provisions is remote. Accordingly, the Company has not recorded any liabilities for any of these agreements as of December 31, 2017.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events On March 2, 2018, the Company amended the task order pursuant and subject to the terms of the Master Services Agreement, dated April 26, 2012, as amended on December 31, 2015, with Medpace, Inc., a clinical research organization conducting global clinical research for the development of drugs and medical devices, to reduce the retainer from $1.3 million to $0.3 million. The retainer is currently recorded as prepaids and other current assets on the Company’s consolidated balance sheets.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	15. Selected Quarterly Financial Data (unaudited, and in thousands, except per share amounts) The following table sets forth the Company’s unaudited consolidated financial results for the last eight fiscal quarters. Three Months Ended Mar. 31, June 30, Sep. 30, Dec. 31, Mar. 31, June 30, Sep. 30, Dec. 31, 2017 2017 2017 2017 2016 2016 2016 2016 Revenue $ 669 $ — $ — $ — $ 640 $ 610 $ 610 $ 676 Net loss: Basic $ (9,834 ) $ (8,842 ) $ (10,159 ) $ (6,623 ) $ (10,086 ) $ (10,446 ) $ (8,954 ) $ (8,537 ) Diluted $ (9,834 ) $ (8,842 ) $ (10,159 ) $ (6,623 ) $ (10,086 ) $ (10,446 ) $ (8,954 ) $ (8,537 ) Shares used in computing net loss per common share: Basic 21,029 21,521 23,678 31,667 14,443 14,493 14,503 19,285 Diluted 21,029 21,521 23,678 31,667 14,443 14,493 14,503 19,285 Net loss per common share(1): Basic $ (0.47 ) $ (0.41 ) $ (0.43 ) $ (0.21 ) $ (0.70 ) $ (0.72 ) $ (0.62 ) $ (0.44 ) Diluted $ (0.47 ) $ (0.41 ) $ (0.43 ) $ (0.21 ) $ (0.70 ) $ (0.72 ) $ (0.62 ) $ (0.44 ) (1) Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarter per-share calculations will not necessarily equal the annual per share calculation.

Summary of Significant Accoun23

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”).
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued a new revenue recognition standard which amends revenue recognition principles and provides a single, comprehensive set of criteria for revenue recognition within and across all industries. The core principle of the guidance is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The guidance also requires improved disclosures on the nature, amount, timing, and uncertainty of revenue that is recognized. In August 2015, the FASB issued an update to the guidance to defer the effective date by one year, such that the new standard will be effective for annual reporting periods beginning after December 15, 2017 and interim periods therein. The standard allows for adoption using a full retrospective method or a modified retrospective method. The Company will apply the new guidance effective January 1, 2018 using the modified retrospective method to contracts that are not completed as of January 1, 2018. The Company’s revenues are derived from license arrangements. The consideration the Company is eligible to receive under the license arrangements includes upfront payments, milestone payments, and royalties. In the fourth quarter of 2017, the Company completed its assessment of the new guidance and the adoption of this guidance, including the cumulative effect of any adjustment to the opening balance of retained earnings, will not have a material impact to its consolidated financial statements. In January 2016, the FASB issued Accounting Standards Update (“ASU”) Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued ASU No. 2016-02, Leases In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Sunesis Europe Limited, a United Kingdom corporation, and Sunesis Pharmaceuticals (Bermuda) Ltd., a Bermuda corporation, as well as a Bermuda limited partnership, Sunesis Pharmaceuticals International LP. All intercompany balances and transactions have been eliminated in consolidation.
Segment Reporting	Segment Reporting Management has determined that the Company operates as a single reportable segment.
Significant Estimates and Judgments	Significant Estimates and Judgments The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the Company’s consolidated financial statements and accompanying notes thereto. Actual results could differ materially from these estimates. Estimates, assumptions and judgments made by management include those related to the valuation of equity and related instruments, revenue recognition, stock-based compensation and clinical trial accounting.
Cash Equivalents and Marketable Securities	Cash Equivalents and Marketable Securities The Company considers all highly liquid securities with original maturities of three months or less from the date of purchase to be cash equivalents, which generally consist of money market funds and corporate debt securities. Marketable securities consist of securities with original maturities of greater than three months, which may include U.S. and European government obligations and corporate debt securities. Management determines the appropriate classification of securities at the time of purchase income equity The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion is included in other income, net in the statements of operations and comprehensive loss. Realized gains and losses and declines in value judged to be other-than-temporary on available-for-sale securities, if any, are also recorded to other income, net. The cost of securities sold is based on the specific-identification method. Invoices for certain services provided to the Company are denominated in foreign currencies. To manage the risk of future movements in foreign exchange rates that would affect such amounts, the Company may purchase certain European currencies or highly-rated investments denominated in those currencies, subject to similar criteria as for other investments defined in the Company’s investment policy. There is no guarantee that the related gains and losses will substantially offset each other, and the Company may be subject to significant exchange gains or losses as currencies fluctuate from quarter to quarter. To date, the Company has purchased Euros and Euro-denominated obligations of foreign governments and corporate debt. As of December 31, 2017 and December 31, 2016, the Company held investments denominated in Euros with an aggregate fair value of $0.8 million and $0.7 million, respectively. Any cash, cash equivalent and short-term investment balances denominated in foreign currencies are recorded at their fair value based on the current exchange rate as of each balance sheet date. The resulting exchange gains or losses and those from amounts payable for services originally denominated in foreign currencies are both recorded in other income, net in the statements of operations and comprehensive loss.
Fair Value Measurements	Fair Value Measurements The Company measures cash equivalents and marketable securities at fair value on a recurring basis using the following hierarchy to prioritize valuation inputs, in accordance with applicable GAAP: Level 1 - quoted prices (unadjusted) in active markets for identical assets and liabilities that can be accessed at the measurement date Level 2 - inputs other than quoted prices included within Level 1 that are observable, either directly or indirectly Level 3 - unobservable inputs The Company’s Level 2 valuations of marketable securities are generally derived from independent pricing services based upon quoted prices in active markets for similar securities, with prices adjusted for yield and number of days to maturity, or based on industry models using data inputs, such as interest rates and prices that can be directly observed or corroborated in active markets. The carrying amounts of the Company’s financial instruments, including
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is determined using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized on a straight-line basis over the shorter of their estimated useful lives or the term of the lease.
Accounting for Royalty Agreement	Accounting for Royalty Agreement The payment of $25.0 million by RPI under the Royalty Agreement (see Note 6) is non-refundable, and no revenue participation right payments will be made unless vosaroxin is T , less $3.1 million initially . The fair value of the warrants was recorded to additional paid-in capital.
Accounting for Notes Payable	Accounting for Notes Payable The accounting for certain fees and expenses related to the Loan Agreement (see Note 8) is as follows. The facility fee is being accounted for as a debt discount and classified within notes payable on the Company’s balance sheet. The fair value of the warrants issued in connection with the Loan Agreement have been recorded as a debt discount within notes payable and an increase to additional paid-in capital on the Company’s balance sheet. The debt discount is being amortized as interest expense over the term of the loan using the effective interest method. The final payment is being accreted as interest expense over the term of the loans using the effective interest method. The legal fees are being accounted for as deferred debt issuance costs within assets on the Company’s balance sheet and are being amortized as other income, net over the term of the loans using the effective interest method.
Revenue Recognition	Revenue Recognition Revenue arrangements with multiple deliverables are accounted for in accordance with the Financial Accounting Standards Board Accounting Standards Codification, Subtopic 605-25, Multiple-Element Arrangements Non-refundable fees where the Company has no continuing performance obligations are recognized as revenues when collection is reasonably assured. In situations where continuing performance obligations exist, non-refundable fees are deferred and recognized ratably over the projected performance period. Milestone payments from license or collaboration agreements which are substantive and at risk at the time the agreement is executed are recognized upon completion of the applicable milestone event. Royalty revenues, if any, will be recognized based on reported product sales by third-party licensees. Research funding from any future agreement will be recognized as the related research services are performed.
Research and Development	Research and Development Research and development expense consists primarily of: (a) clinical trial costs, which include payments for work performed by contract research organizations (“CROs”), clinical trial sites, labs and other clinical service providers, and for drug packaging, storage and distribution; (b) drug manufacturing costs, which include costs for producing drug substance and drug product, and for stability and other testing; (c) personnel costs for related permanent and temporary employees; (d) other outside services and consulting costs; and (e) payments under license agreements. All research and development costs are expensed as they are incurred.
Clinical Trial Accounting	Clinical Trial Accounting The Company records accruals for estimated clinical trial costs, which include payments for work performed by CROs and participating clinical trial sites. These costs are generally a significant component of research and development expense. Costs incurred for setting up clinical trial sites for participation in trials are generally non-refundable, and are expensed as incurred, with any refundable advances related to enrollment of the first patient recorded as prepayments and assessed for recoverability on a quarterly basis. Costs related to patient enrollment are accrued as patients progress through the clinical trial, including amortization of any first-patient prepayments. This amortization generally matches when the related services are rendered, however, these cost estimates may or may not match the actual costs incurred by the CROs or clinical trial sites, and if the Company has incomplete or inaccurate information, the clinical trial accruals may not be accurate. The difference between accrued expenses based on the Company’s estimates and actual expenses have not been significant to date.
Stock-Based Compensation	Stock-Based Compensation The Company grants options to purchase common stock to its employees, directors and consultants under its stock option plans. Under the Company’s Employee Stock Purchase Plan, eligible employees can also purchase shares of the Company’s common stock at 85% of the lower of the fair market value of the Company’s common stock at the beginning of a 12-month offering period or at the end of one of the two related six-month purchase periods. The Company values these share-based awards using the Black-Scholes option valuation model (the “Black-Scholes model”). The determination of fair value of share-based payment awards on the date of grant using the Black-Scholes model is affected by the Company’s stock price as well as assumptions regarding a number of highly complex and subjective variables. These variables include, but are not limited to, the expected stock price volatility over the term of the awards and actual and projected employee stock option exercise behaviors.
Foreign Currency	Foreign Currency Transactions that are denominated in a foreign currency are translated into U.S. dollars at the current exchange rate on the transaction date. Any foreign currency-denominated monetary assets and liabilities are subsequently remeasured at current exchange rates as of each balance sheet date, with gains or losses on foreign exchange recognized in other income, net in the statements of operations and comprehensive loss.
Income Taxes	Income Taxes The Company accounts for income taxes under the liability method. Under this method, deferred tax assets and liabilities are determined based on the differences between the tax basis of assets and liabilities and their basis for financial reporting. Deferred tax assets or liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which temporary differences are expected to be recovered or settled. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company’s policy is to recognize interest charges and penalties in other income, net in the statements of operations and comprehensive loss.

Loss per Common Share (Tables)

Loss per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Computation of Basic and Diluted Loss per Common Share	The following table sets forth the computation of basic and diluted loss per common share for the periods presented (in thousands, except per share amounts): Year Ended December 31, 2017 2016 2015 Numerator: Net loss—basic $ (35,458 ) $ (38,023 ) $ (36,676 ) Net loss—diluted $ (35,458 ) $ (38,023 ) $ (36,676 ) Denominator: Weighted-average common shares outstanding—basic 24,516 15,688 12,156 Weighted-average common shares outstanding—diluted 24,516 15,688 12,156 Net loss per common share: Basic $ (1.45 ) $ (2.42 ) $ (3.02 ) Diluted $ (1.45 ) $ (2.42 ) $ (3.02 )
Schedule of Potential Common Shares Issuable Pursuant to Outstanding Securities Excluded from Computation of Diluted Loss per Common Share	The following table represents the potential common shares issuable pursuant to outstanding securities as of the related period end dates that were excluded from the computation of diluted loss per common share because their inclusion would have had an anti-dilutive effect (in thousands): As of December 31, 2017 2016 2015 Warrants to purchase shares of common stock 5,218 218 938 Convertible preferred stock 6,331 4,270 3,353 Options to purchase shares of common stock 3,532 2,697 2,153 Outstanding securities not included in calculations 15,081 7,185 6,444

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value of Company's Financial Assets Measured on Recurring Basis	The following tables summarize the estimated fair value of the Company’s financial assets measured on a recurring basis as of the dates indicated, which were comprised solely of available-for-sale marketable securities with remaining contractual maturities of one year or less (in thousands): Gross Gross Valuation Amortized Unrealized Unrealized Estimated Fair December 31, 2017 Input Level Cost Gains Losses Value Money market funds Level 1 $ 20,470 $ — $ — $ 20,470 U.S. corporate debt obligations Level 2 3,282 — (5 ) 3,277 U.S. commercial paper Level 2 1,498 — (2 ) 1,496 Total available-for-sale securities 25,250 — (7 ) 25,243 Less amounts classified as cash equivalents (20,470 ) — — (20,470 ) Amounts classified as marketable securities $ 4,780 $ — $ (7 ) $ 4,773 Gross Gross Valuation Amortized Unrealized Unrealized Estimated Fair December 31, 2016 Input Level Cost Gains Losses Value Money market funds Level 1 $ 3,270 $ — $ — $ 3,270 U.S. treasury securities Level 1 16,029 $ — $ (9 ) 16,020 U.S. certificates of deposit Level 1 4,868 $ — $ — 4,868 U.S. corporate debt obligations Level 2 11,617 — (11 ) 11,606 U.S. commercial paper Level 2 2,521 — (2 ) 2,519 Total available-for-sale securities 38,305 — (22 ) 38,283 Less amounts classified as cash equivalents (3,751 ) — — (3,751 ) Amounts classified as marketable securities $ 34,554 $ — $ (22 ) $ 34,532
Summary of Available-for-Sale Securities in Unrealized Loss Position	The following table summarizes the available-for-sale securities that were in an unrealized loss position as of December 31, 2017, each Gross Unrealized Estimated Fair December 31, 2017 Losses Value U.S. corporate debt obligations (5 ) 3,277 U.S. commercial paper (2 ) 1,496 Total available-for-sale securities in an unrealized loss position $ (7 ) $ 4,773

Other Accrued Liabilities (Tabl

Other Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Summary of Other Accrued Liabilities	Other accrued liabilities as of December 31 were as follows (in thousands): 2017 2016 Accrued outside services $ 1,096 $ 1,192 Accrued professional services 471 381 Other accruals 3 118 Total other accrued liabilities $ 1,570 $ 1,691

Notes Payable (Tables)

Notes Payable (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Summary of Future Minimum Payments Under Loan Facility	Aggregate future minimum payments due under the Loan Facility as of December 31, 2017 Year ending December 31, Total 2018 1,586 2019 5,442 2020 2,014 Total minimum payments 9,042 Less amount representing interest (1,542 ) Total notes payable as of December 31, 2017 7,500 Less unamortized debt discount and issuance costs (296 ) Less current portion of notes payable (7,204 ) Non-current portion of notes payable $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Aggregate Non-Cancelable Future Minimum Rental Payments under Operating Leases	Aggregate non-cancelable future minimum rental payments under operating leases as of December 31, 2017, were as follows (in thousands): Year Ending December 31, Payments 2018 $ 514 2019 $ 562 2020 $ 579 2021 $ 294 Total rental payments $ 1,949

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Warrants to Purchase Shares of Company's Common Stock	Warrants to purchase shares of the Company’s common stock outstanding as of December 31, 2017 were as follows (in thousands, except per share amounts): Exercise Price Date Issued Shares Per Share Expiration February 2015 10 $ 13.32 February 2020 March 2016 208 $ 3.25 March 2021 October 2017 5,000 $ 3.00 October 2018 Total warrants outstanding and exercisable 5,218
Shares of Common Stock Reserved for Future Issuance	Shares of the Company’s common stock reserved for future issuance as of December 31, 2017 Shares Available Total for Future Outstanding Shares Grant Securities Reserved Warrants — 5,218 5,218 Convertible preferred stock — 6,331 6,331 Stock option plans 83 3,532 3,615 Employee stock purchase plan 168 — 168 Total reserved shares of common stock 251 15,081 15,332

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-Based Compensation Expense Related to Company's Stock-Based Awards	The following table summarizes stock-based compensation expense related to the Company’s stock-based awards for the periods indicated (in thousands): Year ended December 31, 2017 2016 2015 Research and development $ 865 $ 1,630 $ 2,856 General and administrative 2,059 2,970 3,292 Employee stock-based compensation expense 2,924 4,600 6,148 Non-employee stock-based compensation expense 109 191 196 Total stock-based compensation expense $ 3,033 $ 4,791 $ 6,344
Summary of Weighted-Average and Total Estimated Grant Date Fair Values of Employee Stock Options Granted	The following table summarizes the weighted-average assumptions used as inputs to the Black-Scholes model, and resulting weighted-average and total estimated grant date fair values of employee stock options granted during the periods indicated: Year Ended December 31, 2017 2016 2015 Assumptions: Expected term (years) 4.8 5.3 5.2 Expected volatility 112.5 % 110.0 % 99.9 % Risk-free interest rate 2.1 % 1.9 % 1.7 % Expected dividend yield 0.0 % 0.0 % 0.0 % Fair value: Weighted-average estimated grant date fair value per share $ 2.68 $ 3.12 $ 6.20 Options granted to employees (in thousands) 1,280 750 531 Total estimated grant date fair value (in thousands) $ 3,434 $ 2,344 $ 3,294
Summary of Stock Option Activity for Company's Stock Option Plans	The following table summarizes stock option activity for the Company’s stock option plans in the periods presented (in thousands, except per share amounts): Weighted Weighted Average Average Number Exercise Remaining Aggregate of Price Per Contractual Intrinsic Shares Share Term (Years) Value Outstanding as of December 31, 2016 2,641 $ 13.50 Options granted 2,105 $ 3.19 Options exercised (8 ) $ 3.00 Options forfeited or expired (1,206 ) $ 17.00 Outstanding as of December 31, 2017 3,532 $ 6.18 7.19 $ 1,064 Vested and expected to vest as of December 31, 2017 3,532 $ 6.18 7.19 $ 1,064 Exercisable as of December 31, 2017 1,327 $ 10.74 4.13 $ 246
Summary of Company's RSU	The following table summarizes the Company's RSU activity for the year ended December 31, 2017 (in thousands, except per share amounts): Number of Performance based restricted stock units Shares Outstanding as of December 31, 2016 56 Stocks granted — Stocks exercised — Stocks cancelled (56 ) Outstanding as of December 31, 2017 —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Loss before Provision for Income Taxes	Loss before the provision for income taxes consisted of the following (in thousands): Year Ended December 31, 2017 2016 2015 U.S. operations $ (24,776 ) $ (26,942 ) $ (23,705 ) Foreign operations (10,682 ) (11,081 ) (12,971 ) Loss before provision for income taxes $ (35,458 ) $ (38,023 ) $ (36,676 )
Income Tax Provision Amount Computed by Applying Statutory Income Tax Rate	The income tax provision differs from the amount computed by applying the statutory income tax rate of 34% to pre-tax loss as follows (in thousands): Year Ended December 31, 2017 2016 2015 Tax (benefit) at statutory federal rate 34.0 % 34.0 % 34.0 % State tax (benefit), net of federal benefit 1.2 0.6 (1.6 ) Foreign tax rate differential (10.2 ) (9.9 ) (12.0 ) Permanent differences (1.0 ) (3.2 ) 2.9 Research and development credits 0.7 1.0 (0.8 ) Change in valuation allowance 127.2 (22.5 ) (22.5 ) Change in tax rate (151.6 ) - - Other (0.3 ) - - Effective tax rate - % - % - %
Significant Components of Deferred Tax Assets	Significant components of the Company’s deferred tax assets for federal and state income taxes are as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Federal and state net operating loss carry-forwards $ 109,714 $ 156,066 Federal and state research credit carry-forwards 14,520 13,177 Capitalized research costs 6,304 4,824 Deferred revenue — 244 Stock-based compensation 4,528 5,739 Property and equipment 83 120 Accrued liabilities 117 207 Gross deferred tax assets 135,266 180,377 Valuation allowance (135,266 ) (180,377 ) Net deferred tax assets $ — $ —
Reconciliation of Unrecognized Tax Benefits	A reconciliation of the Company’s beginning and ending amount of unrecognized tax benefits is follows (in thousands): December 31, 2017 2016 Unrecognized tax benefits at beginning of period $ 1,441 $ 1,381 Increases related to current year tax positions 57 60 Increase related to change in tax rate 271 — Unrecognized tax benefits at the end of period $ 1,769 $ 1,441

Selected Quarterly Financial 32

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Data (Unaudited)	The following table sets forth the Company’s unaudited consolidated financial results for the last eight fiscal quarters. Three Months Ended Mar. 31, June 30, Sep. 30, Dec. 31, Mar. 31, June 30, Sep. 30, Dec. 31, 2017 2017 2017 2017 2016 2016 2016 2016 Revenue $ 669 $ — $ — $ — $ 640 $ 610 $ 610 $ 676 Net loss: Basic $ (9,834 ) $ (8,842 ) $ (10,159 ) $ (6,623 ) $ (10,086 ) $ (10,446 ) $ (8,954 ) $ (8,537 ) Diluted $ (9,834 ) $ (8,842 ) $ (10,159 ) $ (6,623 ) $ (10,086 ) $ (10,446 ) $ (8,954 ) $ (8,537 ) Shares used in computing net loss per common share: Basic 21,029 21,521 23,678 31,667 14,443 14,493 14,503 19,285 Diluted 21,029 21,521 23,678 31,667 14,443 14,493 14,503 19,285 Net loss per common share(1): Basic $ (0.47 ) $ (0.41 ) $ (0.43 ) $ (0.21 ) $ (0.70 ) $ (0.72 ) $ (0.62 ) $ (0.44 ) Diluted $ (0.47 ) $ (0.41 ) $ (0.43 ) $ (0.21 ) $ (0.70 ) $ (0.72 ) $ (0.62 ) $ (0.44 ) (1) Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarter per-share calculations will not necessarily equal the annual per share calculation.

Company Overview - Additional I

Company Overview - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash, cash equivalents and marketable securities	$ 31,800
Accumulated deficit	$ 632,854	$ 597,396
Maturity limits period	24 months
Dollars weighted average maturity limit period	12 months

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)Segment	Dec. 31, 2016USD ($)	Sep. 30, 2012USD ($)
Significant Accounting Policies [Line Items]
Number of reportable segment | Segment	1
Fair value of investments denominated in Euros	$ 0.8	$ 0.7
Common stock offering period	At the beginning of a 12-month offering period or at the end of one of the two related six-month purchase periods.
Employee Stock Purchase Plan [Member]
Significant Accounting Policies [Line Items]
Purchase price of a share as a percentage of fair market value	85.00%
Royalty Agreement [Member]
Significant Accounting Policies [Line Items]
Revenue participation right payments	$ 25		$ 25
Fair value of warrants issued in connection with participation agreement	$ 3.1
Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives of assets	3 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives of assets	5 years

Loss per Common Share - Computa

Loss per Common Share - Computation of Basic and Diluted Loss per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net loss—basic	$ (6,623)		$ (10,159)		$ (8,842)		$ (9,834)		$ (8,537)		$ (8,954)		$ (10,446)		$ (10,086)		$ (35,458)	$ (38,023)	$ (36,676)
Net loss—diluted	$ (6,623)		$ (10,159)		$ (8,842)		$ (9,834)		$ (8,537)		$ (8,954)		$ (10,446)		$ (10,086)		$ (35,458)	$ (38,023)	$ (36,676)
Denominator:
Weighted-average common shares outstanding—basic	31,667		23,678		21,521		21,029		19,285		14,503		14,493		14,443		24,516	15,688	12,156
Weighted-average common shares outstanding—diluted	31,667		23,678		21,521		21,029		19,285		14,503		14,493		14,443		24,516	15,688	12,156
Net loss per common share:
Basic	$ (0.21)	[1]	$ (0.43)	[1]	$ (0.41)	[1]	$ (0.47)	[1]	$ (0.44)	[1]	$ (0.62)	[1]	$ (0.72)	[1]	$ (0.70)	[1]	$ (1.45)	$ (2.42)	$ (3.02)
Diluted	$ (0.21)	[1]	$ (0.43)	[1]	$ (0.41)	[1]	$ (0.47)	[1]	$ (0.44)	[1]	$ (0.62)	[1]	$ (0.72)	[1]	$ (0.70)	[1]	$ (1.45)	$ (2.42)	$ (3.02)
[1]	Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarter per-share calculations will not necessarily equal the annual per share calculation.

Loss per Common Share - Schedul

Loss per Common Share - Schedule of Potential Common Shares Issuable Pursuant to Outstanding Securities Excluded from Computation of Diluted Loss per Common Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding securities not included in calculations	15,081	7,185	6,444
Warrants to purchase shares of common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding securities not included in calculations	5,218	218	938
Options to purchase shares of common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding securities not included in calculations	3,532	2,697	2,153
Convertible preferred stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding securities not included in calculations	6,331	4,270	3,353

Financial Instruments - Fair Va

Financial Instruments - Fair Value of Company's Financial Assets Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Amortized Cost	$ 25,250	$ 38,305
Available-for-sale securities, Gross Unrealized Losses	(7)	(22)
Available-for-sale securities, Estimated Fair Value	25,243	38,283
Less amounts classified as cash equivalents, Amortized Cost	(20,470)	(3,751)
Less amounts classified as cash equivalents, Estimated Fair Value	(20,470)	(3,751)
Amounts classified as marketable securities, Amortized Cost	4,780	34,554
Amounts classified as marketable securities, Gross Unrealized Losses	(7)	(22)
Amounts classified as marketable securities, Estimated Fair Value	4,773	34,532
Level 1 [Member] | Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Amortized Cost	20,470	3,270
Available-for-sale securities, Estimated Fair Value	20,470	3,270
Level 1 [Member] | U.S. treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Amortized Cost		16,029
Available-for-sale securities, Gross Unrealized Losses		(9)
Available-for-sale securities, Estimated Fair Value		16,020
Level 1 [Member] | U.S. certificates of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Amortized Cost		4,868
Available-for-sale securities, Estimated Fair Value		4,868
Level 2 [Member] | U.S. corporate debt obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Amortized Cost	3,282	11,617
Available-for-sale securities, Gross Unrealized Losses	(5)	(11)
Available-for-sale securities, Estimated Fair Value	3,277	11,606
Level 2 [Member] | U.S. commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Amortized Cost	1,498	2,521
Available-for-sale securities, Gross Unrealized Losses	(2)	(2)
Available-for-sale securities, Estimated Fair Value	$ 1,496	$ 2,519

Financial Instruments - Summary

Financial Instruments - Summary of Available-for-Sale Securities in Unrealized Loss Position (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Schedule Of Available For Sale Securities [Line Items]
Gross Unrealized Losses	$ (7)
Estimated Fair Value	4,773
U.S. corporate debt obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Gross Unrealized Losses	(5)
Estimated Fair Value	3,277
U.S. commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Gross Unrealized Losses	(2)
Estimated Fair Value	$ 1,496

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Sales of available-for-sale securities	$ 0	$ 0	$ 0

Other Accrued Liabilities - Sum

Other Accrued Liabilities - Summary of Other Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued outside services	$ 1,096	$ 1,192
Accrued professional services	471	381
Other accruals	3	118
Total other accrued liabilities	$ 1,570	$ 1,691

Royalty Agreement - Additional

Royalty Agreement - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2017	Sep. 30, 2012
Royalty Agreement [Line Items]
Deferred revenue, amortized	$ 0.6	$ 0.9
Revenue participation right payments, rate			6.75%
Revenue participation right payments, term			10 years from the date of first commercial sale
Maximum term of revenue participation right payments			10 years
Royalty Agreement [Member]
Royalty Agreement [Line Items]
Revenue participation right payments			$ 25	$ 25
Fair value of warrants issued in connection with participation agreement			$ 3.1

License Agreements - Additional

License Agreements - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended			3 Months Ended
	Jan. 31, 2014	Jun. 30, 2012	Mar. 31, 2011	Sep. 30, 2017	Dec. 31, 2017
License Agreement Terms [Member] | Takeda License Agreements [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Potential pre-commercialization payments receivable					$ 57.5
Upfront fee paid	$ 0.4
Potential pre-commercialization milestone payments payable	$ 9.2
Biogen And Takeda [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Non refundable upfront amount recognized as revenue due to no further performance obligation			$ 4
Biogen [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Received and recognized milestone revenue		$ 1.5
Milestone payment				$ 2.5
Biogen [Member] | License Agreement Terms [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Potential pre-commercialization payments receivable		$ 58.5

Notes Payable - Additional Info

Notes Payable - Additional Information (Detail) - USD ($)	Jun. 30, 2017	Apr. 01, 2016	Mar. 31, 2016	Oct. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Proceeds from notes payable						$ 15,000,000
Loan Agreement [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 15,000,000
Proceeds from notes payable		$ 2,500,000	12,500,000
Date of Loan and Security Agreement					Oct. 18, 2011
Loan proceeds to repay the outstanding principal			7,200,000
Repayment of outstanding principal			6,000,000
Final payment fee			1,200,000
Accrued interest			45,000
Facility fee			100,000
Legal fees			$ 100,000
Line of credit facility final payment, additional amount due	$ 312,500
Percentage of penalty for prepaying loan after maturity	0.50%
Prepayment penalty expiration date					Jun. 30, 2017
Maturity date					Apr. 1, 2020
Warrants expiration term					5 years
Number of warrants issued					208,002
Warrants exercise price for shares					$ 3.2454
Estimated fair value of warrants issued					$ 500,000
Loan Agreement [Member] | Warrants to purchase shares of common stock [Member]
Debt Instrument [Line Items]
Common stock price					$ 3.24
Exercise price					$ 3.2454
Risk-free interest rates					1.21%
Expected volatility					111.96%
Expected term					5 years
Dividend yield					0.00%
Loan Agreement [Member] | Extension of Maturity Date [Member]
Debt Instrument [Line Items]
Percentage of penalty for prepaying loan before maturity	1.00%
Prepayment penalty expiration date					Mar. 31, 2018
Loan Agreement [Member] | LIBOR Rate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	8.54%
Amended Loan Agreement [Member]
Debt Instrument [Line Items]
Description of monthly interest payment					The Amendment modified the loan repayment terms to be interest-only through July 1, 2018, followed by twenty-two (22) equal monthly payments of principal and interest through the maturity date, contingent upon receipt of at least Fifteen Million Dollars ($15,000,000) in unrestricted cash proceeds received after June 1, 2017 from the issuance by the Company of new equity securities any time after June 1, 2017 through December 31, 2017. Thereafter and until the scheduled maturity date of April 1, 2020, in addition to interest accrued during such period, the monthly payments will include an amount equal to the outstanding principal divided by 28 months, unless the interest only period is extended by a further six months, in which case the amortization period will be 22 months.
Debt instrument, minimum threshold amount of unrestricted cash proceeds from issuance of new equity for principal and interest only payment period	$ 15,000,000
Loan, Covenant description					Pursuant to the Loan Agreement and the amendments, the Company is bound by a variety of affirmative covenants during the term of the Loan Agreement, including, without limitation, certain information delivery requirements, notice requirements and obligations to maintain certain insurance. Additionally, the Company is bound by certain negative covenants setting forth actions that are not permitted to be taken during the term of the Amended Loan Agreement without the Lenders’ consent, including, without limitation, incurring certain additional indebtedness, making certain asset dispositions, entering into certain mergers, acquisitions or other business combination transactions or incurring any non-permitted lien or other encumbrance on the Company’s assets. Upon the occurrence of an event of default under the Amended Loan Agreement (subject to cure periods for certain events of default), all amounts owed by the Company thereunder would begin to bear interest at a rate that is 5.0% higher than the rate that would otherwise be applicable and may be declared immediately due and payable by the Collateral Agent. Events of default under the Amended Loan Agreement include, among other things, the following: the occurrence of certain bankruptcy events; the failure to make payments under the Loan Agreement when due; the occurrence of a material impairment on the Collateral Agent’s security interest over the collateral, a material adverse change in the business, operations or condition (financial or otherwise) of the Company or material impairment of the prospect of repayment of the obligations under the Amended Loan Agreement; the occurrence of a default under certain other agreements entered into by the Company; the rendering of certain types of judgments against the Company; the revocation of certain government approvals of the Company; any breach by the Company of any covenant (subject to cure periods for certain covenants) made in the Amended Loan Agreement; and the failure of any representation or warranty made by the Company in connection with the Amended Loan Agreement to be correct in all material respects when made. The Amended Loan Agreement defines certain events of default, including instances of a Material Adverse Change in its operations, which may require prepayment of the outstanding loan. In the event of default by the Company under the Loan Agreement, the Lenders would be entitled to exercise their remedies thereunder, including the right to accelerate the debt, upon which the Company may be required to repay all amounts then outstanding under the Loan Agreement, which could harm the Company's financial condition. The Company was in compliance with all applicable covenants set forth in the Loan Agreement as of December 31, 2017 and 2016. The principal payments due under the Loan Agreement have been classified as a current liability at December 31, 2017 due to the considerations discussed in Note 1 and the assessment that the material adverse change clause under the Loan Agreement is not within the Company's control. The Company has not been notified of an event of default by the Lenders as of the date of the filing of this Form 10-K.
Second Amendment [Member]
Debt Instrument [Line Items]
Description of monthly interest payment					On October 31, 2017, the Company entered into a second amendment to the Amended Loan Agreement (the “Second Amendment”). The Second amendment modified the loan repayment terms to add two additional extended interest-only periods beyond July 1, 2018. If under the terms of the Amended Loan Agreement, the interest-only period has been extended to July 1, 2018, the Company may further extend the interest-only period to October 1, 2018, contingent upon the receipt of at least Fifteen Million dollars ($15,000,000) in unrestricted net cash proceeds from the issuance by the Company of new equity securities or as a non-refundable upfront payment on a new business development agreement or royalty financing agreement (the “New Capital”), on or after October 24, 2017, but on or prior to December 31, 2017. Subsequently, the Company may further extend the interest-only period to January 1, 2019, contingent upon the receipt of at least Twenty-Five Million dollars ($25,000,000) in New Capital (inclusive of any prior amounts received after October 24, 2017), on or after October 24, 2017, but on or prior to September 15, 2018.
Second Amendment Period One [Member]
Debt Instrument [Line Items]
Debt instrument, minimum threshold amount of unrestricted cash proceeds from issuance of new equity for principal and interest only payment period				$ 15,000,000
Second Amendment Period Two [Member]
Debt Instrument [Line Items]
Debt instrument, minimum threshold amount of unrestricted cash proceeds from issuance of new equity for principal and interest only payment period				$ 25,000,000

Notes Payable - Summary of Futu

Notes Payable - Summary of Future Minimum Payments Under Loan Facility (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total notes payable as of December 31, 2017	$ 7,500
Less current portion of notes payable	(7,204)	$ (3,333)
Non-current portion of notes payable		$ 11,102
Notes payable [Member]
Debt Instrument [Line Items]
2,018	1,586
2,019	5,442
2,020	2,014
Total minimum payments	9,042
Less amount representing interest	(1,542)
Less unamortized debt discount and issuance costs	$ (296)

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Commitments And Contingencies Disclosure [Line Items]
Rent expense | $	$ 0.7	$ 0.6	$ 0.5
Original Operating Lease [Member]
Commitments And Contingencies Disclosure [Line Items]
Operating lease, office space leased	15,378
Operating lease expiration date	Apr. 30, 2015
Operating lease agreement, original date	2014-01
Amended Operating Lease [Member]
Commitments And Contingencies Disclosure [Line Items]
Operating lease, additional office space leased	6,105
Operating lease expiration date	Jun. 30, 2015
Operating lease agreement, date of amendment	2014-06
Lease property description	The lease has been amended in January 2015 and September 2015 to extend the expiration date to December 31, 2016 and in September 2016, respectively and in May 2016, the lease was again amended to extend the expiration date to June 30, 2018.
Second Amended Operating Lease [Member]
Commitments And Contingencies Disclosure [Line Items]
Operating lease expiration date	Dec. 31, 2016
Operating lease agreement, date of amendment	2015-01
Further Amended Operating Lease [Member]
Commitments And Contingencies Disclosure [Line Items]
Operating lease expiration date	Sep. 30, 2016
Operating lease agreement, date of amendment	2015-09
Fourth Amended Operating Lease [Member]
Commitments And Contingencies Disclosure [Line Items]
Operating lease expiration date	Jun. 30, 2018
Operating lease agreement, date of amendment	2016-05
Fifth Amended Operating Lease [Member]
Commitments And Contingencies Disclosure [Line Items]
Operating lease expiration date	Jun. 30, 2021
Operating lease agreement, date of amendment	2017-12
Lease property description	The lease was last amended in December 2017 to remove the 6,105 square feet of additional office space added in June 2014 and to extend the expiration date to June 30, 2021, with an option to extend the lease for two additional years.
Operating lease, additional office space removed	6,105
Operating lease, option to extend, description	Option to extend the lease for two additional years.
Operating lease, renewal term	2 years

Commitments and Contingencies46

Commitments and Contingencies - Aggregate Non-Cancelable Future Minimum Rental Payments under Operating Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,018	$ 514
2,019	562
2,020	579
2,021	294
Total rental payments	$ 1,949

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information 1 (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended					12 Months Ended
	Nov. 30, 2017	Oct. 31, 2017	Oct. 31, 2016	Dec. 31, 2015	Apr. 30, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Aug. 31, 2011
Stockholders Equity [Line Items]
Preferred stock, shares authorized						10,000,000	10,000,000
Preferred stock, shares outstanding						17,697	17,897
Common stock, voting rights						One vote per share
Shares of common stock issued						34,291,000	20,925,000
Preferred stock, shares issued						18,000	18,000
Proceeds from issuance of common shares, gross			$ 27,900	$ 26,200
Proceeds from issuance of common stock through controlled equity offering facilities, net			$ 25,900	$ 25,200		$ 13,877	$ 20,367	$ 8,709
Total warrants outstanding, shares						5,218,000
Common Stock [Member]
Stockholders Equity [Line Items]
Shares of common stock issued				14,420,000		34,291,000	20,925,000	14,420,000	11,017,000
Underwritten Offering [Member]
Stockholders Equity [Line Items]
Price per common share			$ 3.85	$ 5.04				$ 5.04
Shares of common stock issued		7,500,000	5,675,825	1,832,698				1,832,698
Proceeds from issuance of common shares, gross		$ 20,000
Proceeds from issuance of common stock through controlled equity offering facilities, net		$ 18,500
Warrants, exercise price per share		$ 3
Underwritten Offering [Member] | Common Stock Warrants [Member]
Stockholders Equity [Line Items]
Price per common share		$ 2
Total warrants outstanding, shares		3,750,000
Number of shares called by each warrant		0.5
Underwritten Offering [Member] | Preferred Stock Warrants [Member]
Stockholders Equity [Line Items]
Price per common share		$ 2,000
Total warrants outstanding, shares		1,250,000
Number of shares called by each warrant		500
Over-Allotment Option [Member]
Stockholders Equity [Line Items]
Shares of common stock issued				239,047				239,047
Controlled Equity Offering Facilities [Member]
Stockholders Equity [Line Items]
Proceeds from issuance of common shares, gross						$ 14,200
Proceeds from issuance of common stock through controlled equity offering facilities, net						$ 14,200
Issuance of common stock, offering value										$ 20,000
Common stock sales agreement, date						2011-08
Issuance of common stock, remaining offering value						$ 45,000
Controlled Equity Offering Facilities [Member] | Common Stock [Member]
Stockholders Equity [Line Items]
Price per common share						$ 2.72
Common stock, shares sold						5,321,151
Additional Controlled Equity Offerings Facilities [Member]
Stockholders Equity [Line Items]
Increase in aggregate controlled equity offering agreement as per amendment	$ 45,000				$ 30,000
Issuance of common stock, commission percentage, maximum	3.00%				3.00%
Common stock sales agreement further amended, date						2017-11
Common stock sales agreement amended, date						2013-04
Series B Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Price per common share				$ 840		$ 840		$ 840
Shares issued upon conversion				166		166		166
Preferred stock, shares issued				20,200				20,200
Series B Convertible Preferred Stock [Member] | Maximum [Member]
Stockholders Equity [Line Items]
Percentage of outstanding common stock				9.98%				9.98%
Series B, Series C and Series D Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred stock, payment to stock holders in the event of liquidation, dissolution or winding up preference per share						$ 0.0001
Preferred stock, voting rights						Shares of Series B, Series C, and Series D Stock will generally have no voting rights, except as required by law and except that the consent of holders of a majority of the outstanding Series B and Series C Stock will be required to amend the terms of the Series B, Series C, and Series D Stock.
Series B, Series C and Series D Convertible Preferred Stock [Member] | Maximum [Member]
Stockholders Equity [Line Items]
Percentage of outstanding common stock						9.98%
Series C Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Price per common share			$ 3,850			$ 3,850
Shares issued upon conversion			1,000			1,000
Preferred stock, shares issued			1,558
Series C Convertible Preferred Stock [Member] | Maximum [Member]
Stockholders Equity [Line Items]
Percentage of outstanding common stock			9.98%
Series D Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Price per common share						$ 2,000
Shares issued upon conversion						1,000
Series D Convertible Preferred Stock [Member] | Underwritten Offering [Member]
Stockholders Equity [Line Items]
Shares issued upon conversion		1,000
Preferred stock, shares issued		2,500
Series D Convertible Preferred Stock [Member] | Maximum [Member] | Underwritten Offering [Member]
Stockholders Equity [Line Items]
Percentage of outstanding common stock		9.98%

Stockholders' Equity - Additi48

Stockholders' Equity - Additional Information 2 (Detail) - shares	Jul. 10, 2017	Jan. 02, 2017	Jan. 02, 2016	Jun. 03, 2011	Dec. 31, 2017
Stockholders Equity [Line Items]
Number of shares of common stock reserved for issuance under latest plan					15,332,000
Shares Available for Future Grant					251,000
Options granted, Number of Shares	543,650				2,105,000
2011 Plan [Member]
Stockholders Equity [Line Items]
Number of shares of common stock reserved for issuance under latest plan				1,006,976
Shares Available for Future Grant				89,967	82,585
Shares of common stock available for issuance		836,981	576,785	733,333
Common stock available for issuance automatic increase period					10 years
Common stock available for issuance automatic increase maximum number of shares					4.00%
Options granted, Number of Shares					2,105,293
Stock Option Plans [Member]
Stockholders Equity [Line Items]
Number of shares of common stock reserved for issuance under latest plan					3,615,000
Shares Available for Future Grant					83,000
Stock Option Plans [Member] | 2011 Plan [Member]
Stockholders Equity [Line Items]
Shares Available for Future Grant				183,676
Stock Option Plans [Member] | New Employees [Member]
Stockholders Equity [Line Items]
Option exercisable on first anniversary of vesting commencement date, percent					25.00%
Portion of option exercisable for each month over vesting percent					2.083%
Stock option plans, vesting period					4 years
Vesting rights					New employees, of which 25% of the shares subject to such options become exercisable on the first anniversary of the vesting commencement date, and 1/48th of the shares subject to such options become exercisable each month over the remainder of the four-year vesting period
Stock Option Plans [Member] | Existing Employees [Member]
Stockholders Equity [Line Items]
Vesting rights					Existing employees with various vesting schedules over three to four years
Stock Option Plans [Member] | Existing Employees [Member] | Minimum [Member]
Stockholders Equity [Line Items]
Stock option plans, vesting period					3 years
Stock Option Plans [Member] | Existing Employees [Member] | Maximum [Member]
Stockholders Equity [Line Items]
Stock option plans, vesting period					4 years
Stock Option Plans [Member] | New Non-Employee Board Members [Member]
Stockholders Equity [Line Items]
Stock option plans, vesting period					2 years
Vesting rights					New non-employee members of the board of directors, of which 50% of the shares subject to such options become exercisable on each of the first and second anniversary of the vesting commencement date
Option exercisable on first and second anniversary of vesting commencement date, percent					50.00%
Stock Option Plans [Member] | Continuing Non-Employee Board Members [Member]
Stockholders Equity [Line Items]
Portion of option exercisable for each month over vesting percent					4.166%
Stock option plans, vesting period					2 years
Vesting rights					Continuing non-employee members of the board of directors, of which 1/24th of the shares subject to such options become exercisable each month following the date of grant over a two-year vesting period

Stockholders' Equity - Additi49

Stockholders' Equity - Additional Information 3 (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)PurchasePeriodshares	Dec. 31, 2016shares
Stockholders Equity [Line Items]
Share of common stock value | $	$ 25,000
Number of shares issued under employee stock purchase plan	87,020	59,086
Shares Available for Future Grant	251,000
Employee Stock Purchase Plan [Member]
Stockholders Equity [Line Items]
Purchase price of a share as a percentage of fair market value	85.00%
Duration of offering period	12 months
Number of purchase periods in each offering period | PurchasePeriod	2
Duration of each purchase period	6 months
Number of shares authorized under employee stock purchase plan	83,333
Common stock available for issuance automatic increase period	10 years
Common stock available for issuance automatic increase maximum number of shares	1.00%
Shares Available for Future Grant	168,404

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Warrants to Purchase Shares of Company's Common Stock (Detail) shares in Thousands	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Class of Warrant or Right [Line Items]
Total warrants outstanding and exercisable, shares	5,218
February 2015 [Member]
Class of Warrant or Right [Line Items]
Total warrants outstanding and exercisable, shares	10
Warrants, Exercise Price Per Share | $ / shares	$ 13.32
Warrants Expiration Date	2020-02
March 2016 [Member]
Class of Warrant or Right [Line Items]
Total warrants outstanding and exercisable, shares	208
Warrants, Exercise Price Per Share | $ / shares	$ 3.25
Warrants Expiration Date	2021-03
October 2017 [Member]
Class of Warrant or Right [Line Items]
Total warrants outstanding and exercisable, shares	5,000
Warrants, Exercise Price Per Share | $ / shares	$ 3
Warrants Expiration Date	2018-10

Stockholders' Equity - Shares o

Stockholders' Equity - Shares of Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2017shares
Class of Stock [Line Items]
Shares Available for Future Grant	251,000
Outstanding Securities	15,081,000
Total Shares Reserved	15,332,000
Warrants [Member]
Class of Stock [Line Items]
Outstanding Securities	5,218,000
Total Shares Reserved	5,218,000
Stock Option Plans [Member]
Class of Stock [Line Items]
Shares Available for Future Grant	83,000
Outstanding Securities	3,532,000
Total Shares Reserved	3,615,000
Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Shares Available for Future Grant	168,404
Total Shares Reserved	168,000
Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Outstanding Securities	6,331,000
Total Shares Reserved	6,331,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense Related to Company's Stock-Based Awards (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation, Allocation and Classification in Financial Statements
Total stock-based compensation expense	$ 3,033	$ 4,791	$ 6,344
Employee stock-based compensation expense [Member]
Share-based Compensation, Allocation and Classification in Financial Statements
Total stock-based compensation expense	2,924	4,600	6,148
Non-employee stock-based compensation expense [Member]
Share-based Compensation, Allocation and Classification in Financial Statements
Total stock-based compensation expense	109	191	196
Research and development [Member]
Share-based Compensation, Allocation and Classification in Financial Statements
Total stock-based compensation expense	865	1,630	2,856
General and administrative [Member]
Share-based Compensation, Allocation and Classification in Financial Statements
Total stock-based compensation expense	$ 2,059	$ 2,970	$ 3,292

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	Jul. 10, 2017	Jun. 09, 2017	Feb. 11, 2016	Feb. 25, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Tender offer announcement date					Jun. 9, 2017
Options to purchase shares of common stock	778,928	781,505
New options granted to purchase shares of common stock	543,650				2,105,000
Exercise price of options	$ 2.62
Incremental expense for vested options					$ 50,957
Estimated fair value of stock options, vested					1,900,000	$ 4,600,000	$ 5,800,000
Payment of cash dividends					$ 0
Dividend yield ratio					0.00%
Intrinsic value of options exercised						$ 0	$ 200,000
Tax benefits related to stock option exercised					$ 0
Unrecognized stock-based compensation cost related to unvested stock options					$ 4,100,000
Weighted average term of unrecognized stock-based compensation expense					2 years 8 months 12 days
Performance Based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price per share				$ 0
2011 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
New options granted to purchase shares of common stock					2,105,293
Number of stock awards vested			122,000
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Intrinsic value of options exercised					$ 100,000
Options Priced from $8.00-$19.99 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exchange ratio applied to options priced		130.00%
Exercise price of applied option price, minimum		$ 8
Exercise price of applied option price, maximum		$ 19.99
Options Priced for $20.00 or Greater [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exchange ratio applied to options priced		175.00%
Exercise price of applied option price, minimum		$ 20

Stock-Based Compensation - Su54

Stock-Based Compensation - Summary of Weighted-Average and Total Estimated Grant Date Fair Values of Employee Stock Options Granted (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 10, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assumptions:
Expected dividend yield		0.00%
Fair value:
Options granted to employees (in thousands)	543,650	2,105,000
Stock Option Plans [Member]
Assumptions:
Expected term (years)		4 years 9 months 18 days	5 years 3 months 18 days	5 years 2 months 12 days
Expected volatility		112.50%	110.00%	99.90%
Risk-free interest rate		2.10%	1.90%	1.70%
Expected dividend yield		0.00%	0.00%	0.00%
Fair value:
Weighted-average estimated grant date fair value per share		$ 2.68	$ 3.12	$ 6.20
Stock Option Plans [Member] | Employee stock-based compensation expense [Member]
Fair value:
Options granted to employees (in thousands)		1,280,000	750,000	531,000
Total estimated grant date fair value (in thousands)		$ 3,434	$ 2,344	$ 3,294

Stock-Based Compensation - Su55

Stock-Based Compensation - Summary of Stock Option Activity for Company's Stock Option Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 10, 2017	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding, Beginning Balance, Number of Shares		2,641,000
Options granted, Number of Shares	543,650	2,105,000
Options exercised, Number of Shares		(8,000)
Options forfeited or expired, Number of Shares		(1,206,000)
Outstanding, Ending Balance, Number of Shares		3,532,000
Vested and expected to vest as of December 31, 2017, Number of Shares		3,532,000
Exercisable as of December 31, 2017, Number of Shares		1,327,000
Outstanding, Beginning Balance, Weighted Average Exercise Price Per Share		$ 13.50
Options granted, Weighted Average Exercise Price Per Share		3.19
Options exercised, Weighted Average Exercise Price Per Share		3
Options forfeited or expired, Weighted Average Exercise Price Per Share		17
Outstanding, Ending Balance, Weighted Average Exercise Price Per Share		6.18
Vested and expected to vest as of December 31, 2017, Weighted Average Exercise Price Per Share		6.18
Exercisable as of December 31, 2017, Weighted Average Exercise Price Per Share		$ 10.74
Outstanding, Weighted Average Remaining Contractual Term (Years)		7 years 2 months 8 days
Vested and expected to vest as of December 31, 2017, Weighted Average Remaining Contractual Term (Years)		7 years 2 months 8 days
Exercisable as of December 31, 2017, Weighted Average Remaining Contractual Term (Years)		4 years 1 month 17 days
Outstanding, Aggregated Intrinsic Value		$ 1,064
Vested and expected to vest as of December 31, 2017, Aggregate Intrinsic Value		1,064
Ending Balance, Exercisable, Aggregate Intrinsic Value		$ 246

Stock-Based Compensation - Su56

Stock-Based Compensation - Summary of Company's RSU (Detail) - Performance Based Restricted Stock Units [Member] shares in Thousands	12 Months Ended
	Dec. 31, 2017shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Beginning Balance, Number of Shares	56
Stocks cancelled, Number of Shares	(56)

Income Taxes - Loss before Prov

Income Taxes - Loss before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S. operations	$ (24,776)	$ (26,942)	$ (23,705)
Foreign operations	(10,682)	(11,081)	(12,971)
Loss before provision for income taxes	$ (35,458)	$ (38,023)	$ (36,676)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Income tax provision		$ 0	$ 0	$ 0
Statutory income tax rate		34.00%	34.00%	34.00%
Unrecognized tax benefits that would have tax impact		$ 0
Net valuation allowance (decreased) increased		(45,100,000)	$ 8,500,000	$ 8,400,000
Unrecognized tax benefit		1,769,000	$ 1,441,000	$ 1,381,000
Decrease in deferred tax assets and valuation allowance due to enacted tax act		53,700,000
Scenario plan [Member]
Income Taxes [Line Items]
Statutory income tax rate	21.00%
Domestic tax authority [Member]
Income Taxes [Line Items]
Net operating loss carry-forwards		432,900,000
Research and development tax credit carry-forwards		$ 8,500,000
Net operating loss carry-forwards expiration		2,018
State and local jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carry-forwards		$ 269,000,000
Research and development tax credit carry-forwards		$ 7,400,000
Net operating loss carry-forwards expiration		2,018

Income Taxes - Income Tax Provi

Income Taxes - Income Tax Provision Amount Computed by Applying Statutory Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax (benefit) at statutory federal rate	34.00%	34.00%	34.00%
State tax (benefit), net of federal benefit	1.20%	0.60%	(1.60%)
Foreign tax rate differential	(10.20%)	(9.90%)	(12.00%)
Permanent differences	(1.00%)	(3.20%)	2.90%
Research and development credits	0.70%	1.00%	(0.80%)
Change in valuation allowance	127.20%	(22.50%)	(22.50%)
Change in tax rate	(151.60%)
Other	(0.30%)

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Federal and state net operating loss carry-forwards	$ 109,714	$ 156,066
Federal and state research credit carry-forwards	14,520	13,177
Capitalized research costs	6,304	4,824
Deferred revenue		244
Stock-based compensation	4,528	5,739
Property and equipment	83	120
Accrued liabilities	117	207
Gross deferred tax assets	135,266	180,377
Valuation allowance	$ (135,266)	$ (180,377)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Unrecognized tax benefits at beginning of period	$ 1,441	$ 1,381
Increases related to current year tax positions	57	60
Increase related to change in tax rate	271
Unrecognized tax benefits at the end of period	$ 1,769	$ 1,441

Guarantees and Indemnification

Guarantees and Indemnification - Additional Information (Detail)	Dec. 31, 2017USD ($)
Guarantees [Abstract]
Liabilities incurred in indemnification agreements	$ 0

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Master Services Agreement [Member] - Prepaid Expenses And Other Current Assets [Member] - USD ($) $ in Millions	Mar. 02, 2018	Dec. 31, 2015
Subsequent Event [Line Items]
Clinical research for development of drugs and medical devices		$ 1.3
Subsequent Event [Member]
Subsequent Event [Line Items]
Clinical research for development of drugs and medical devices	$ 0.3

Selected Quarterly Financial 64

Selected Quarterly Financial Data - Schedule of Quarterly Financial Data (Unaudited) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue							$ 669		$ 676		$ 610		$ 610		$ 640		$ 669	$ 2,536	$ 3,061
Net loss:
Basic	$ (6,623)		$ (10,159)		$ (8,842)		(9,834)		(8,537)		(8,954)		(10,446)		(10,086)		(35,458)	(38,023)	(36,676)
Diluted	$ (6,623)		$ (10,159)		$ (8,842)		$ (9,834)		$ (8,537)		$ (8,954)		$ (10,446)		$ (10,086)		$ (35,458)	$ (38,023)	$ (36,676)
Shares used in computing net loss per common share:
Basic	31,667		23,678		21,521		21,029		19,285		14,503		14,493		14,443		24,516	15,688	12,156
Diluted	31,667		23,678		21,521		21,029		19,285		14,503		14,493		14,443		24,516	15,688	12,156
Net loss per common share:
Basic	$ (0.21)	[1]	$ (0.43)	[1]	$ (0.41)	[1]	$ (0.47)	[1]	$ (0.44)	[1]	$ (0.62)	[1]	$ (0.72)	[1]	$ (0.70)	[1]	$ (1.45)	$ (2.42)	$ (3.02)
Diluted	$ (0.21)	[1]	$ (0.43)	[1]	$ (0.41)	[1]	$ (0.47)	[1]	$ (0.44)	[1]	$ (0.62)	[1]	$ (0.72)	[1]	$ (0.70)	[1]	$ (1.45)	$ (2.42)	$ (3.02)
[1]	Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarter per-share calculations will not necessarily equal the annual per share calculation.