Achaogen (AKAOQ) 10-K 15 Mar 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Mar. 04, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Trading Symbol	AKAO
Entity Registrant Name	Achaogen Inc
Entity Central Index Key	1,301,501
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		18,395,219
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 98.7

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 20,287	$ 18,881
Short-term investments	38,444	44,798
Contracts receivable	5,039	5,234
Prepaids and other current assets	1,719	520
Total current assets	65,489	69,433
Property and equipment, net	905	725
Restricted cash	127	127
Deposit and other assets	342	37
Total assets	66,863	70,322
Current liabilities:
Accounts payable	3,537	2,122
Accrued liabilities	4,927	3,266
Other current liabilities	225	128
Total current liabilities	8,689	5,516
Loan payable, long-term	14,536	0
Other long-term liabilities	479	193
Total liabilities	$ 23,704	$ 5,709
Commitments and contingencies (Note 7)
Stockholders’ equity:
Common stock, $0.001 par value, 290,000,000 shares authorized, 18,395,219 and 17,907,135 shares issued and outstanding at December 31, 2015 and 2014, respectively	$ 18	$ 18
Preferred stock, $0.001 par value, 10,000,000 shares authorized, no shares issued and outstanding	0	0
Additional paid-in capital	219,182	213,527
Accumulated deficit	(175,993)	(148,900)
Accumulated other comprehensive loss	(48)	(32)
Total stockholders’ equity	43,159	64,613
Total liabilities and stockholders’ equity	$ 66,863	$ 70,322

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	290,000,000	290,000,000
Common stock, shares issued	18,395,219	17,907,135
Common stock, shares outstanding	18,395,219	17,907,135
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Contract revenue	$ 26,061	$ 19,970	$ 18,512
Operating expenses:
Research and development	40,228	30,110	23,484
General and administrative	12,406	9,646	6,992
Total operating expenses	52,634	39,756	30,476
Loss from operations	(26,573)	(19,786)	(11,964)
Interest expense	(699)	(397)	(1,331)
Other income, net	179	7	183
Net loss	$ (27,093)	$ (20,176)	$ (13,112)
Basic and diluted net loss per common share (in dollars per share)	$ (1.49)	$ (1.42)	$ (33.83)
Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share (in shares)	18,147,986	14,210,098	387,547

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net loss	$ (27,093)	$ (20,176)	$ (13,112)
Other comprehensive loss:
Net unrealized losses on available-for-sale securities	(16)	(32)	0
Total comprehensive loss	$ (27,109)	$ (20,208)	$ (13,112)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) Statement - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2012		7,120,608
Convertible preferred stock, beginning balance at Dec. 31, 2012		$ 100,354
Increase (Decrease) in Convertible Preferred Stock:
Sale of shares of Series D convertible preferred stock, net of issuance costs (in shares)		1,864,788
Sale of shares of Series D convertible preferred stock, net of issuance costs		$ 22,200
Issuance of shares of Series D convertible preferred stock in exchange for convertible notes and interest payable to related parties (in shares)		227,784
Issuance of shares of Series D convertible preferred stock in exchange for convertible notes and interest payable to related parties		$ 2,732
Issuance of shares of Series D convertible preferred stock upon conversion of the related-party loan payable to The Wellcome Trust (in shares)		583,162
Issuance of shares of Series D convertible preferred stock upon conversion of the related-party loan payable to The Wellcome Trust		$ 6,992
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2013		9,796,342
Convertible preferred stock, ending balance at Dec. 31, 2013		$ 132,278
Beginning balance (in shares) at Dec. 31, 2012			373,840
Beginning balance at Dec. 31, 2012	$ (112,578)		$ 0	$ 3,034	$ (115,612)	$ 0
Increase (Decrease) in Stockholders' Equity:
Conversion of preferred stock to common stock upon initial public offering	$ 0
Issuance of common stock under stock plans (in shares)	19,004		19,004
Issuance of common stock under stock plans	$ 61			61
Reclassification of warrant liability to additional paid-in capital	0
Stock-based compensation expense	1,053			1,053
Unrealized loss on available-for-sale securities, net of taxes	0
Net loss	(13,112)				(13,112)
Ending balance at Dec. 31, 2013	(124,576)		$ 0	4,148	(128,724)	0
Ending balance (in shares) at Dec. 31, 2013			392,844
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2014		0
Convertible preferred stock, ending balance at Dec. 31, 2014		$ 0
Increase (Decrease) in Stockholders' Equity:
Conversion of preferred stock to common stock upon initial public offering (in shares)		(9,796,342)	(10,386,894)
Conversion of preferred stock to common stock upon initial public offering	(132,278)	$ (132,278)	$ (11)	(132,267)
Issuance of common stock upon initial public offering, net of issuance costs (in shares)			6,900,000
Issuance of common stock upon initial public offering, net of issuance costs	73,936		$ 7	73,929
Issuance of common stock upon exercise of warrant (in shares)			909
Issuance of common stock upon exercise of warrant	$ 2			2
Issuance of common stock under stock plans (in shares)	208,693		208,693
Issuance of common stock under stock plans	$ 706			706
Issuance of common stock under ESPP (in shares)			17,795
Issuance of common stock under ESPP	139			139
Reclassification of warrant liability to additional paid-in capital	286			286
Stock-based compensation expense	2,050			2,050
Unrealized loss on available-for-sale securities, net of taxes	(32)					(32)
Net loss	(20,176)				(20,176)
Ending balance at Dec. 31, 2014	$ 64,613		$ 18	213,527	(148,900)	(32)
Ending balance (in shares) at Dec. 31, 2014	17,907,135		17,907,135
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2015		0
Convertible preferred stock, ending balance at Dec. 31, 2015		$ 0
Increase (Decrease) in Stockholders' Equity:
Conversion of preferred stock to common stock upon initial public offering	$ 0
Issuance of common stock upon initial public offering, net of issuance costs (in shares)			197,838
Issuance of common stock upon initial public offering, net of issuance costs	$ 1,319		$ 0	1,319
Issuance of common stock under stock plans (in shares)	190,128		228,504
Issuance of common stock under stock plans	$ 1,053			1,053
Issuance of common stock under ESPP (in shares)			61,742
Issuance of common stock under ESPP	300			300
Reclassification of warrant liability to additional paid-in capital	0
Stock-based compensation expense	2,983			2,983
Unrealized loss on available-for-sale securities, net of taxes	(16)					(16)
Net loss	(27,093)				(27,093)
Ending balance at Dec. 31, 2015	$ 43,159		$ 18	$ 219,182	$ (175,993)	$ (48)
Ending balance (in shares) at Dec. 31, 2015	18,395,219		18,395,219

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (27,093)	$ (20,176)	$ (13,112)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	426	358	506
Amortization of premium on short-term investments	500	257	0
Stock-based compensation expense	2,983	2,050	1,053
Revaluation of convertible preferred stock warrant	0	42	0
Revaluation of derivative liability	19	0	0
Loss on asset disposition	0	0	10
Non-cash interest expense relating to notes payable	302	209	472
Non-cash interest expense relating to related-party convertible loan payable	0	0	197
Non-cash restructuring charges	0	0	196
Change in operating assets and liabilities:
Contracts receivable	195	1,996	(2,972)
Prepaids and other assets	(1,504)	1,397	(1,456)
Accounts payable and accrued liabilities	3,076	(539)	1,450
Other liabilities	8	123	(198)
Net cash used in operating activities	(21,088)	(14,283)	(13,854)
Cash flows from investing activities:
Purchase of property and equipment	(606)	(340)	(110)
Purchase of short-term investments	(41,851)	(45,087)	0
Maturities and sale of short-term investments	47,689	0	0
Net cash provided by (used in) investing activities	5,232	(45,427)	(110)
Cash flows from financing activities:
Proceeds from initial public offering, net of issuance costs	0	73,936	0
Proceeds from issuance of convertible preferred stock, net of issuance costs	0	0	22,200
Proceeds from sales of common stock, net of issuance costs	1,319	0	0
Proceeds from the issuance of common stock in connection with equity incentive plans	1,353	811	61
Proceeds from exercise of stock warrants	0	2	0
Proceeds from loans payable, net of issuance costs	14,590	0	0
Repayment of notes payable	0	(6,896)	(4,632)
Net cash provided by financing activities	17,262	67,853	17,629
Net increase in cash and cash equivalents	1,406	8,143	3,665
Cash and cash equivalents, beginning of year	18,881	10,738	7,073
Cash and cash equivalents, end of year	20,287	18,881	10,738
Supplemental disclosures of cash flow information
Interest paid	396	221	693
Supplemental disclosures of noncash investing and financing information
Conversion of related-party convertible loan and notes payable to convertible preferred stock	0	0	9,724
Conversion of convertible preferred stock into common stock	0	132,278	0
Reclassification of warrant liability to additional paid-in capital	$ 0	$ 286	$ 0

Organization and Basis of Prese

Organization and Basis of Presentation and Consolidation	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation and Consolidation	Organization and Basis of Presentation and Consolidation Achaogen, Inc. (together with its consolidated subsidiary, the “Company”) is a clinical-stage biopharmaceutical company committed to the discovery, development, and commercialization of novel antibacterial drugs to treat multi-drug resistant gram-negative infections. The Company is developing plazomicin, its lead product candidate, for the treatment of bacterial infections due to multi-drug resistant Enterobacteriaceae, including carbapenem-resistant Enterobacteriaceae ("CRE"). The Company’s Phase 3 study of plazomicin in the treatment of patients with complicated urinary tract infections ("cUTI") and acute pyelonephritis ("AP"), entitled EPIC (Evaluating Plazomicin In cUTI), is expected to serve as a single pivotal study supporting a new drug application ("NDA") for plazomicin in the United States. In addition, the Company is completing a Phase 3 study of plazomicin, the CARE (Combating Antibiotic Resistant Enterobacteriaceae) trial, which is a resistant pathogen-specific trial designed to evaluate the efficacy and safety of plazomicin in patients with infections due to CRE. The Company was incorporated in Delaware in 2002 and commenced operations in 2004. Since commencing operations in 2004, the Company has devoted substantially all of its resources to identifying and developing its product candidates, including conducting preclinical studies and clinical trials and providing general and administrative support for these operations. Basis of Presentation and Consolidation The consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) and include the consolidated accounts of the Company and its subsidiary. Intercompany accounts and transactions have been eliminated in consolidation. During 2012, the Company established a wholly owned foreign subsidiary in the United Kingdom. There have been no significant activities for this entity during the fiscal years ended December 31, 2015, 2014 and 2013. On April 7, 2015, the Company filed a Registration Statement on Form S-3, declared effective by the SEC on April 21, 2015, covering the offering of up to $150.0 million of common stock, preferred stock, debt securities, warrants, purchase contracts and/or units. This Registration Statement included a prospectus covering the offering, issuance and sale of up to $30.0 million of shares of our common stock from time to time in an "at-the-market" ("ATM") equity offering pursuant to a sales agreement with Cowen and Company, LLC. As of December 31, 2015, the Company had sold 197,838 shares pursuant to its ATM equity offering program at a weighted-average price of $7.05 per share for aggregate offering proceeds of $1.4 million and aggregate net proceeds of $1.3 million , after deducting the sales commissions and offering expenses. In March 2014, the Company completed its initial public offering ("IPO") of shares of its common stock, pursuant to which the Company issued 6,900,000 shares of common stock, which includes 900,000 shares issued pursuant to the over-allotment option granted to its underwriters, and received net proceeds of approximately $73.9 million , after deducting underwriting discounts, commissions and offering expenses. In connection with the completion of the Company's IPO, all shares of convertible preferred stock converted into 10,386,894 shares of common stock and all of the Company's convertible preferred stock warrants were converted into warrants to purchase common stock. The Company has incurred losses and negative cash flows from operations every year since its inception. As of December 31, 2015, the Company had unrestricted cash, cash equivalents and short-term investments of approximately $58.7 million and an accumulated deficit of approximately $176.0 million . Management expects to continue to incur additional substantial losses in the foreseeable future as a result of the Company’s research and development activities, and the amounts of unrestricted cash, cash equivalents and short-term investments held at December 31, 2015 are not sufficient to fund projected levels of expenditures during 2016 without securing additional funding sources. Management plans to raise additional funds through equity or debt financing arrangements, government contracts, and/or third party collaboration funding. However, there can be no assurance that such funding sources will be available at terms acceptable to the Company or at all. If the Company is unable to raise additional funding to meet its working capital needs, it will be forced to delay or reduce the scope of its research programs and/or limit or cease its operations. The lack of financial resources to fund projected negative cash flows and the resultant need to raise substantial additional funding in the near term in order to sustain operations raise substantial doubt as to the Company’s ability to continue as a going concern. The accompanying financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The financial statements do not reflect any adjustments relating to the recoverability and reclassification of assets and liabilities that might be necessary if the Company is unable to continue as a going concern.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Use of Estimates The accompanying financial statements have been prepared in accordance with U.S. GAAP. The preparation of financial statements in conformity with U.S. GAAP requires management to make judgments, assumptions and estimates that affect the reported amounts of assets, liabilities, revenues and expenses and related disclosures of contingent liabilities. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of derivative liabilities, common stock and stock-based awards and income taxes. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates. Fair Value of Financial Instruments The carrying amounts of the Company’s financial instruments, including cash and cash equivalents, contracts receivable, prepaid and other current assets, accounts payable, accrued liabilities, and other current liabilities approximate fair value due to their short-term maturities. Short-term investments consist of available-for-sale securities as of December 31, 2015 and are carried at fair value. Based upon the borrowing rates currently available to the Company for loans with similar terms, the Company believes the carrying amounts of the loan payable and the derivative liability also represent fair values. Cash and Cash Equivalents Cash equivalents include only securities having an original maturity of three months or less at the time of purchase. As of December 31, 2015 and 2014, cash and cash equivalents consisted of bank deposits, cash, and investments in money market funds. Short-term Investments Short-term investments consist of debt securities with maturities greater than three months, but less than one year from the date of acquisition, and are classified as available for sale. Short-term investments are carried at fair value. Unrealized gains and losses on available-for-sale securities are excluded from earnings and are reported as a component of net unrealized losses on available-for-sale securities in the Company's consolidated statements of comprehensive loss. The amortized cost of debt securities reflects amortization of purchase premiums and accretion of purchase discounts to date, which is included in interest income. The Company reviews all of its marketable securities on a regular basis to evaluate whether any security has experienced an other-than-temporary decline in fair value. Restricted Cash At December 31, 2015 and 2014, the Company had long-term restricted cash of $127,000 . The restricted cash, which consists of a money market account with one of the Company’s financial institutions, serves as collateral for a letter of credit provided as a security deposit under the Company’s facility lease. The facility lease expires on April 14, 2017 . Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. The Company has one operating segment. Customer Concentration For the years ended December 31, 2015, 2014 and 2013, all of the Company’s revenue has been generated solely from funding pursuant to U.S. government contracts, and accordingly all contracts receivable relate to funding from U.S. government contracts. Concentration of Credit Risk Financial instruments that potentially subject the Company to a significant concentration of credit risk consist of cash, cash equivalents and short-term investments. Cash and cash equivalents are deposited in checking and money market accounts at one financial institution, which at times, may exceed federally insured limits. Management believes that the financial institution is financially sound, and, accordingly, minimal credit risk exists with respect to this financial institution. Our investment policy limits investments to certain types of debt securities issued by the U.S. government, its agencies and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The Company is exposed to credit risk in the event of default by the institutions holding its cash and cash equivalents or issuing the debt securities. As of December 31, 2015, the Company has not experienced any credit losses in such accounts or investments. Contracts Receivable Contracts receivable represent amounts owed to the Company under certain government contracts. The Company had no amounts reserved for doubtful accounts as of December 31, 2015 and 2014, as the Company expects full collection of the receivable balances. Property and Equipment, Net Property and equipment consists of office equipment, laboratory equipment, and leasehold improvements and is stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over their estimated useful lives or the remaining lease term, whichever is shorter. Maintenance and repair costs are recorded as a component of operating expenses in the Company’s consolidated statement of operations when incurred. Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. If indicators of impairment exist, an impairment loss would be recognized when the estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment charge is determined based upon the excess of the carrying value of the asset over its estimated fair value, with estimated fair value determined based upon an estimate of discounted future cash flows or other appropriate measures of estimated fair value. For the year ended December 31, 2013, the Company recorded impairment charges of $194,000 related to the cessation of use of leasehold improvements and property and equipment in certain areas of leased property. See Note 14 for further information regarding the restructuring activities and the impairment. Convertible Preferred Stock Warrant Liabilities The Company accounted for its Series A and Series C convertible preferred stock warrants as freestanding warrants for shares that are puttable or redeemable. At December 31, 2013, these warrants were classified as liabilities on the consolidated balance sheet at their estimated fair value. At the end of each reporting period, changes in estimated fair value during the period were recorded as a component of other income, net. At the time of the IPO, the warrants to purchase preferred stock were converted into warrants to purchase common stock, which are no longer subject to remeasurement, and the preferred stock warrant liability was reclassified to additional paid-in capital at its then fair value. Stock-Based Compensation The Company measures and recognizes the compensation expense for all stock-based awards made to employees and directors, including employee stock options, stock grants and employee stock purchases related to the Employee Stock Purchase Plan (“ESPP”) based on estimated fair values. The Company uses the Black-Scholes option-pricing valuation model to estimate the grant-date fair value of stock option and ESPP awards with time-based vesting terms. The determination of fair value for stock-based awards on the date of grant using an option-pricing model requires management to make certain assumptions regarding a number of complex and subjective variables. The fair value of restricted stock unit (“RSU”) awards with time-based vesting terms is based on the grant date share price. The Company recognizes stock-based compensation cost over the award’s requisite service period on a straight-line basis for time-based awards and on a graded basis for awards that are contingent on the achievement of market-based conditions. The Company records stock-based compensation expense, net of the estimated impact of forfeited awards. As such, the Company recognizes stock-based compensation expense only for those stock-based awards that are expected to vest over their requisite service period, based on the vesting provisions of the individual underlying grants. During 2014 and 2013, the Company issued stock-based option awards with market-based conditions that vest upon achievement of certain market price thresholds of the Company’s common stock. The estimated fair value for market-based stock option awards is determined using a lattice valuation model with a Monte-Carlo simulation. The model takes into consideration the historical volatility of the Company’s stock and the risk-free interest rate at the date of grant. In addition, the model is used to estimate the derived service period for the awards. The derived service period is the estimated period of time that would be required to satisfy the market condition, assuming the market condition will be satisfied. Stock-based compensation expense is recognized over the implicit service period derived from the Monte-Carlo simulation model, as applicable, but is accelerated if the market condition is achieved earlier than estimated. For non-employee stock-based awards, the measurement date on which the estimated fair value of the stock-based award is calculated is equal to the earlier of (i) the date at which a commitment for performance by the counterparty to earn the equity instrument is reached or (ii) the date at which the counterparty’s performance is complete. The Company recognizes stock-based compensation expense for the estimated fair value of the vested portion of non-employee awards. Revenue Recognition The Company recognizes revenue when: (i) evidence of an arrangement exists, (ii) fees are fixed or determinable, (iii) services have been delivered, and (iv) collectability is reasonably assured. The Company currently generates revenue entirely from government contracts. Government contracts are agreements that provide the Company with payments for certain types of expenditures in return for research and development activities over a contractually defined period. Revenue from government contracts is recognized in the period during which the related costs are incurred and the related services are rendered, provided that the applicable conditions under the government contracts have been met. Costs of contract revenue are recorded as a component of operating expenses in the Company's consolidated statements of operations. Funds received from third parties under contract arrangements are recorded as revenue if the Company is deemed to be the principal participant in the contract arrangements because the activities under the contracts are part of the Company’s development programs. If the Company is not the principal participant, the funds from contracts are recorded as a reduction to research and development expense. Contracts funds received are not refundable and are recognized when the related qualified research and development costs are incurred and when there is reasonable assurance that the funds will be received. Funds billed and received in advance are recorded as deferred revenue. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses include certain payroll and personnel expenses; laboratory supplies; consulting costs; external contract research and development expenses; and allocated overhead, including rent, equipment depreciation and utilities, and relate to both Company-sponsored programs as well as costs incurred pursuant to collaboration agreements and government contracts. Nonrefundable advance payments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized and recognized as an expense as the goods are delivered or the related services are performed. The Company estimates preclinical study and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on its behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the receipt of the related services are recorded as prepaid expenses until the services are rendered. Leases The Company has entered into lease agreements for its laboratory and office facilities. These leases qualify as and are accounted for as operating leases. Rent expense is recognized on a straight-line basis over the term of the lease and, accordingly, the Company records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Incentives granted under the Company’s facilities leases, including allowances to fund leasehold improvements and rent holidays, are capitalized and are recognized as reductions to rental expense on a straight-line basis over the term of the lease. Income Taxes The Company uses the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits. The tax benefit recognized in the financial statements for a particular tax position is the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company's policy is to recognize interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense. Net Loss and Per Share Basic net loss per common share is computed by dividing the net loss by the weighted-average number of common shares outstanding during the period. Diluted net loss per common share is computed by dividing the net loss by the weighted-average number of common shares and dilutive common share equivalents outstanding during the period. Because the Company has reported a net loss for the years ended December 31, 2015, 2014 and 2013, diluted net loss per common share is the same as basic net loss per common share for those periods. Effective as of the completion of the IPO, all of the Company’s preferred stock was converted to common stock. For purposes of calculating net loss per common share for the year ended December 31, 2014, the preferred stock converted to common stock was included in the net loss per common share calculation on a post-conversion basis based on the conversion date. The following table sets forth the computation of the basic and diluted net loss per share during the years ended December 31, 2015, 2014 and 2013 (in thousands, except share and per share amounts): Year Ended December 31, 2015 2014 2013 Net loss $ (27,093 ) $ (20,176 ) $ (13,112 ) Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share 18,147,986 14,210,098 387,547 Basic and diluted net loss per common share $ (1.49 ) $ (1.42 ) $ (33.83 ) The following potentially dilutive securities outstanding have been excluded from the computations of diluted weighted-average shares outstanding because such securities have an anti-dilutive impact due to losses reported (in common stock equivalent shares): December 31, 2015 2014 2013 Convertible preferred stock — — 10,386,894 Warrants to purchase convertible preferred stock — — 40,454 Options to purchase common stock 2,387,337 1,885,372 1,405,550 Restricted stock units 372,024 168,200 — Warrants to purchase common stock 30,024 40,454 909 Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition . This ASU is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. The ASU's effective date is for interim and annual periods beginning after December 15, 2017. Adoption of the ASU is either retrospective to each prior period presented or retrospective with a cumulative adjustment to retained earnings or accumulated deficit as of the adoption date. Early adoption is permitted. The Company is assessing the potential effects of this ASU on its consolidated financial statements. In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern (Topic 205-40), Going Concern . This ASU introduces an explicit requirement for management to assess if there is substantial doubt about an entity's ability to continue as a going concern, and to provide related footnote disclosures in certain circumstances. In connection with each annual and interim period, management must assess if there is substantial doubt about an entity's ability to continue as a going concern within one year after the issuance date. Disclosures are required if conditions give rise to substantial doubt. ASU 2014-15 is effective for all entities in the first annual period ending after December 15, 2016. The Company is currently assessing the potential effects of this ASU on its consolidated financial statements. In January 2015, the FASB issued ASU No. 2015-01, Income Statement - Extraordinary and Unusual Items (Subtopic 225-20) - Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items . This guidance eliminates from GAAP the concept of extraordinary items and is effective for annual reporting periods, including interim reporting periods, beginning after December 15, 2015, and is applicable to the Company's fiscal year beginning January 1, 2016. Early adoption is permitted. The Company does not anticipate it will have a material impact to its consolidated financial statements. In April 2015, the FASB issued ASU No. 2015-03, Simplifying the Presentation of Debt Issuance Costs , to require debt issuance costs to be presented as an offset against debt outstanding. The ASU is effective for interim and annual periods beginning after December 15, 2015 and early adoption is permitted. Application is retrospective to each prior period presented. The Company elected to adopt this standard during the twelve-months ended December 31, 2015. As a result, all issuance costs associated with the Company’s loan payable issued during the twelve-months ended December 31, 2015 have been classified as a debt discount. The adoption of this standard did not impact the Company’s consolidated balance sheet as of December 31, 2014, or the consolidated statements of operations, comprehensive loss or cash flows for any period presented. In November 2015, the FASB issued ASU No. 2015-17, Income Taxes (Topic 740) - Balance Sheet Classification of Deferred Taxes . This guidance simplifies the presentation of deferred income taxes in a classified balance sheet to require that deferred tax liabilities and assets be classified as noncurrent and is effective for annual reporting periods, including interim reporting periods, beginning after December 15, 2016, and is applicable to the Company's fiscal year beginning January 1, 2017. Early adoption is permitted. The Company does not anticipate it will have a material impact to its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases, which, for operating leases, requires a lessee to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its balance sheet. The standard also requires a lessee to recognize a single lease cost, calculated so that the cost of the lease is allocated over the lease term, on a generally straight-line basis. This ASU will be effective for the Company in fiscal year 2019. Early adoption is permitted. The Company is currently assessing the impact of this ASU and anticipates the new guidance will have a material impact to its consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash, cash equivalents, contracts receivable, accounts payable, and accrued liabilities, approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 : Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. During the periods presented, the Company has not changed the manner in which it values liabilities that are measured at estimated fair value using Level 3 inputs. There were no transfers within the hierarchy during the years ended December 31, 2015 and 2014. Financial instruments Financial assets and liabilities measured and recognized at fair value on a recurring basis were as follows (in thousands): As of December 31, 2015: Amortized Unrealized Unrealized Fair Value Assets Cash $ 1,013 $ — $ — $ 1,013 Level 1: Restricted cash 127 — — 127 Money market funds 19,274 — — 19,274 Subtotal 19,401 — — 19,401 Level 2: Corporate debt securities 34,490 — (47 ) 34,443 Commercial paper 1,997 — — 1,997 U.S. Treasury bills 2,005 — (1 ) 2,004 Subtotal 38,492 — (48 ) 38,444 Total $ 58,906 $ — $ (48 ) $ 58,858 Reported as: Cash and cash equivalents $ 20,287 Short-term investments $ 38,444 Restricted cash $ 127 Liabilities Level 3: Derivative liability $ 375 As of December 31, 2014: Amortized Unrealized Unrealized Fair Value Assets Cash $ 620 $ — $ — $ 620 Level 1: Restricted cash 127 — — 127 Money market funds 18,261 — — 18,261 Subtotal 18,388 — — 18,388 Level 2: Corporate debt securities 44,830 — (32 ) 44,798 Total $ 63,838 $ — $ (32 ) $ 63,806 Reported as: Cash and cash equivalents $ 18,881 Short-term investments $ 44,798 Restricted cash $ 127 All available-for-sale securities held as of December 31, 2015 had contractual maturities of less than one year. There were no sales of available-for-sale securities in any of the periods presented. The fair value of corporate and U.S. Treasury debt obligations that were in unrealized loss positions totaled $36.5 million as of December 31, 2015. The Company has determined that (i) it does not have the intent to sell any of these investments, and (ii) it is not more likely than not that it will be required to sell any of these investments before recovery of the entire amortized cost basis. The Company anticipates that it will recover the entire amortized cost basis of such corporate and U.S. Treasury debt obligations and has determined that no other-than-temporary impairments associated with credit losses were required to be recognized during the year ended December 31, 2015. The following table provides a summary of changes in the estimated fair value of the Company’s liabilities measured at estimated fair value using significant Level 3 inputs for the years ended 2015, 2014 and 2013 (in thousands): Estimated Estimated Balance at December 31, 2012 $ 237 $ 1,398 Change in estimated fair value of convertible preferred stock warrant liabilities included in other income, net 7 — Extinguishment of derivative liability — (1,398 ) Balance at December 31, 2013 244 — Change in estimated fair value of convertible preferred stock warrant liabilities included in other income, net 42 — Reclassification of warrant liability to additional paid-in capital upon conversion of warrant to purchase convertible preferred stock to warrant to purchase common stock (286 ) — Balance at December 31, 2014 — — Issuance of Level 3 derivative liability — 356 Increase in estimated fair value — 19 Balance at December 31, 2015 $ — $ 375 Pursuant to the loan and security agreement with Solar Capital Ltd. (see Note 8), the Company entered into a Success Fee Agreement under which the Company agreed to pay $1.0 million (the "Success Fee") if the Company obtains FDA approval to market plazomicin. If such approval is obtained, the Success Fee shall be due the later of (i) August 5, 2019 or (ii) the date such FDA approval is obtained. The fair value of the Success Fee, approximately $356,000 at the date of issuance, is recorded as a derivative liability and included in other long-term liabilities on the accompanying consolidated balance sheet. The estimated fair value of the derivative liability as of December 31, 2015 increased by $19,000 from August 5, 2015 which amount is recorded as a component of other income, net for the year ended December 31, 2015. The fair value of the derivative liability was determined using a discounted cash flow analysis, and is classified as a Level 3 measurement within the fair value hierarchy since the Company’s valuation utilized significant unobservable inputs. Specifically, the key assumptions included in the calculation of the estimated fair value of the derivative instrument include: i) the Company’s estimates of both the probability and timing of a potential $1.0 million payment to Solar Capital Ltd. upon FDA approval to market plazomicin, and ii) a discount rate of 13% which was derived from the Company's estimated cost of debt. The estimated fair value of the derivative liability is most sensitive to the probability of FDA approval. Should the probability of FDA approval change by 5% , the fair value of the derivative liability as of December 31, 2015 would change by approximately $30,000 . Any changes in the estimated fair value will result in an entry to other income, net. The convertible preferred stock warrant liabilities and derivative liabilities associated with certain convertible loans were considered Level 3 liabilities. The estimated fair values of the outstanding preferred stock warrant liabilities were measured using the Black-Scholes option-pricing model. The estimated fair value of the derivative liability associated with the convertible loan due to beneficial conversion features ("BCF"), on certain of the Company’s convertible loans was measured by multiplying (1) the intrinsic value of the 20% conversion discount on the effective date and (2) the number of shares converted. In connection with the conversion of the related-party loan payable to The Wellcome Trust to shares of Series D convertible preferred stock in March 2013, the estimated fair value of the derivative liability of $1,398,000 was reclassified to convertible preferred stock. The fair value of the convertible preferred stock warrant liabilities was estimated to be $244,000 as of December 31, 2013 using the following assumptions: Year Ended December 31, 2013 Preferred stock fair value per share $10.89–$12.43 Volatility 65%–68% Risk-free interest rate 0.2%–2.6% Remaining contractual term (in years) 1.2–7.8 Dividend yield 0% In connection with the completion of the Company's IPO in March 2014, all of the outstanding warrants to purchase convertible preferred stock converted into warrants to purchase 40,454 shares of common stock at a weighted-average exercise price of $12.36 per share. The Company remeasured the estimated fair value of these remaining warrants at the date of the conversion and recorded a $42,000 loss related to the change in estimated fair value as part of other income, net, and reclassified the estimated fair value of $286,000 to additional paid-in capital.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	Balance Sheet Components Property and Equipment Property and equipment consisted of the following (in thousands): December 31, 2015 2014 Office equipment $ 1,144 $ 1,033 Laboratory equipment 3,161 2,932 Leasehold improvements 1,072 1,000 5,377 4,965 Less: accumulated depreciation and amortization (4,472 ) (4,240 ) Property and equipment, net $ 905 $ 725 Depreciation and amortization expense for the years ended December 31, 2015, 2014 and 2013 was $426,000 , $358,000 and $506,000 , respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): December 31, 2015 2014 Accrued clinical and development expenses $ 2,869 $ 1,618 Payroll and related bonus expenses 1,615 1,171 Other 443 477 $ 4,927 $ 3,266 Other Long-term Liabilities Other long-term liabilities consisted of the following (in thousands): December 31, 2015 2014 Derivative liability $ 375 $ — Deferred rent 104 193 $ 479 $ 193

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License and Collaboration Agreements	License and Collaboration Agreements Ionis Pharmaceuticals In January 2006, the Company entered into a license agreement with Ionis Pharmaceuticals, Inc. ("Ionis"). Ionis granted the Company an exclusive, worldwide license with the right to grant and authorize sublicenses related to the research and development of aminoglycoside products. As an up-front fee, the Company issued 97,402 shares of preferred Series A convertible stock at a fair value of $15.40 per share. This license fee of $1,500,000 was recorded as research and development expense in 2006. In further consideration of this license, and in accordance with the terms of the agreement, the Company is required to make milestone payments with respect to development, regulatory and commercialization milestones, and to pay a percentage of revenue received from sublicensees (if any). All such milestone and sublicense revenue payments may total, in the aggregate, up to but no more than $19,500,000 for the first product and $9,750,000 following the second product commercialized under the agreement with Ionis. The Company is also required to pay additional milestone payments of up to $20,000,000 in the aggregate upon the first achievement of specified threshold levels of annual net sales of all aminoglycoside products in a calendar year. The license agreement also provides that the Company shall pay royalties equal to a low single-digit percentage of annual worldwide net sales of all licensed products, including plazomicin. Through December 31, 2013, the Company had compensated Ionis $3,000,000 in connection with the first two milestones under the license for the first aminoglycoside product candidate. In 2014, the Company met its third milestone under the license with Ionis when it dosed the first patients in the Phase 3 CARE trial for plazomicin, and made the milestone payment of $4,000,000 , which was recorded as research and development expense. As of December 31, 2015 and December 31, 2014, the Company had no outstanding payments due under the agreement.

Government Contracts

Government Contracts	12 Months Ended
	Dec. 31, 2015
Research and Development [Abstract]
Government Contracts	Government Contracts Certain of the Company’s drug discovery and development activities are performed under contracts with U.S. government agencies. Management has determined that the Company is the principal participant in the following contract arrangements, and, accordingly, the Company records amounts earned under the arrangements as revenue. Costs incurred under revenue contracts are recorded as operating expenses in the Company' consolidated statements of operations. Biomedical Advanced Research and Development Authority In August 2010, the Company was awarded a contract with the Biomedical Advanced Research and Development Authority ("BARDA"), for the development, manufacturing, nonclinical and clinical evaluation of, and regulatory filings for, plazomicin as a countermeasure for disease caused by antibiotic-resistant pathogens and biothreats. The original contract included committed funding of $27,600,000 for the first two years of the contract and subsequent options exercisable by BARDA to provide additional funding. In September 2012, BARDA modified the contract to increase the total contract committed funding to $43,398,000 through March 2014 . In April 2013, the Company was awarded an additional $60,410,000 under the contract to support its Phase 3 CARE clinical trial of plazomicin which increased the total committed funding under this contract to $103,808,000 . As of December 31, 2015, $26,731,000 was remaining available from funding committed under this contract. During the years ended December 31, 2015, 2014 and 2013, the Company recognized revenue of $17,569,000 , $19,970,000 and $18,073,000 , respectively, under this agreement, of which $4,657,000 and $5,234,000 were included in contracts receivable at December 31, 2015, and 2014, respectively. Defense Threat Reduction Agency In November 2012, the Defense Threat Reduction Agency ("DTRA"), a division of the U.S. Department of Defense, terminated for convenience a contract with the Company that provided funding for the Company's LpxC inhibitor program. In connection with the termination, the Company sought payment from DTRA for additional expenses the Company has incurred. Effective April 30, 2015, the Company reached a settlement of its claim with DTRA. The net settlement of $7,122,000 was recorded as contract revenue during the year ended December 31, 2015. Together with sums previously received, it constitutes complete and final settlement of the contract. National Institute for Allergy and Infectious Disease In September 2008, the Company was awarded a contract by the National Institute for Allergy and Infectious Disease, or NIAID, to conduct research and development of extended-spectrum aminoglycoside antibiotics for the treatment of serious gram-negative infections. As amended in September 2011, this contract provided the Company with up to $22,188,000 over a five -year term through August 2013. In July 2014, the Company was awarded a one -year, $407,000 grant by NIAID to conduct discovery research on novel antibiotics targeting gram-negative bacteria. In July 2015, NIAID extended the grant term through July 31, 2016. In July 2015, the Company was awarded a contract by NIAID for $1.5 million through June 30, 2016, with additional funding of up to $3.0 million available if all options are exercised under the contract. In January 2016, the contract was modified with an additional $508,000 funding commitment through June 30, 2016. During the years ended December 31, 2015, 2014 and 2013, the Company recognized revenue of $1,370,000 , zero and $168,000 , respectively, under these agreements, of which $382,000 and zero were included in contracts receivable at December 31, 2015 and 2014, respectively.

Commitments

Commitments	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments	Commitments Facility Lease Agreement In December 2010, the Company entered into an amended and restated lease agreement for its facility in South San Francisco, consisting of approximately 35,000 square feet. As part of the amended and restated lease agreement, the landlord agreed to complete certain leasehold improvement work on the additional premises in the amount of $362,000 . Such tenant allowance was recorded as a leasehold improvement and is being amortized over the term of the lease. In April 2013, the Company subleased 19,000 square feet to a subtenant through March 2014. In June 2013, the Company further amended its lease to extend the lease term for the remaining space of approximately 16,000 square feet through April 2017 and to terminate the lease on the subleased space effective March 2014. The Company has provided a letter of credit in the amount of $127,000 as a security deposit on the lease, which letter of credit is collateralized by a money market account. The Company records the collateralized deposit as restricted cash. In May 2015, the Company entered into an office lease agreement for approximately 6,000 square feet in South San Francisco through August 31, 2017. The Company recognizes rent expense on a straight-line basis over the lease period and has accrued for rent expense incurred but not paid. Aggregate rent expense, net of sublease income, was $526,000 , $405,000 and $673,000 for the years ended December 31, 2015, 2014 and 2013, respectively. The Company received zero , $97,000 and $291,000 of sublease income for the years ended December 31, 2015, 2014 and 2013, respectively. Future minimum payments under all noncancelable operating leases as of December 31, 2015, are as follows (in thousands): 2016 $ 776 2017 313 Total minimum lease payments $ 1,089 Nonrefundable advance payments In July 2015, the Company entered into an agreement with its pharmaceutical contract manufacturing organization that obligates it to make a total of $1,500,000 of nonrefundable advance payments for the reservation of facilities and resources, plus procurement of long lead raw materials, to produce plazomicin for regulatory commercial validation. Such advance payments are initially capitalized as prepaid and other current assets and will be recognized as research and development expenses as goods are delivered and services are performed. The Company assesses such prepaid and other current assets for impairment if events or changes in circumstances indicate that the carrying amount may not be recoverable or may not provide future economic benefits. As of December 31, 2015, the Company had recorded $944,000 as prepaid and other current assets related to this agreement and recognized $56,000 as research and development expenses during the year ended December 31, 2015. One remaining installment of $500,000 becomes due in March 2016. Guarantees and Indemnifications As permitted under Delaware law and in accordance with the Company’s bylaws, the Company is required to indemnify its officers and directors for certain events or occurrences while the officer or director is or was serving in such capacity. The Company is also party to indemnification agreements with its directors. The Company believes the fair value of the indemnification rights and agreements is minimal. Accordingly, the Company has not recorded any liabilities for these indemnification rights and agreements as of December 31, 2015 and 2014.

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Borrowings	Borrowings Solar Capital Ltd. Loan Agreement On August 5, 2015, the Company entered into a loan and security agreement (the “Loan Agreement”) with Solar Capital Ltd. (the “Lender”) pursuant to which the Lender agreed to make available to the Company term loans in an aggregate principal amount of up to $25.0 million with a maturity date of August 5, 2019, subject to certain conditions to funding. An initial $15.0 million term loan was funded at closing on August 5, 2015, and funding of an additional $10.0 million term loan is contingent upon the Company receiving at least $25.0 million in net proceeds from the sale of its common stock by no later than August 15, 2016. Borrowings under the term loans bear interest per annum at 6.99% plus the greater of 1% or the one-month LIBOR. The Company is currently required to make interest-only payments through February 2017 and, beginning on March 1, 2017, the Company is required to make monthly payments of interest plus equal monthly payments of principal over a term of 30 months. If the Company receives $35.0 million in net proceeds from the sale or issuance of stock, convertible subordinated notes, collaboration agreements, grants or research or development contracts and achieves 50% enrollment in its Phase 3 EPIC trial, in each case prior to March 1, 2017, the Company will be permitted to make interest-only payments through August 2017, rather than February 2017 and, beginning on September 1, 2017 the Company would be required to make monthly payments of interest plus equal monthly payments of principal over a term of 24 months . The Loan Agreement requires collateral by a security interest in all of the Company’s assets except intellectual property (which is subject to a negative pledge) and contains customary affirmative and negative covenants, and also includes standard events of default, including payment defaults. Upon the occurrence of an event of default, a default interest rate of an additional 4% may be applied to the outstanding loan balances, and the Lender may declare all outstanding obligations immediately due and payable and take such other actions as set forth in the Loan Agreement. There were no financial covenants attached to the loan. The Loan Agreement included a closing fee of $250,000 which was paid at closing, and the Company is obligated to pay a fee equal to 8% of the term loans funded upon the earliest to occur of the maturity date, the acceleration of the term loans or the voluntary prepayment of the term loans. The cost of these fees is being amortized as interest expense over the term of the loan using the effective-interest method. The Company may voluntarily prepay all, but not less than all, of the outstanding term loans. The Loan Agreement contains customary representations, warranties and covenants. In addition, the Loan Agreement contains customary events of default that entitle the Lender to cause the Company’s indebtedness under the Loan Agreement to become immediately due and payable. On August 5, 2015, pursuant to the Loan Agreement, the Company entered into a Success Fee Agreement with the Lender under which the Company agreed to pay the Lender $1.0 million if the Company obtains FDA approval to market plazomicin. If such approval is obtained, the success fee shall be due the later of (i) August 5, 2019 or (ii) the date such FDA approval is obtained. The fair value of the Success Fee at the date of issuance of approximately $356,000 was recorded as a debt discount and is being amortized as interest expense over the term of the loan using the effective-interest method. Future principal debt payments on the loan payable are as follows (in thousands): December 31, 2015 2016 $ — 2017 5,000 2018 6,000 2019 4,000 Total principal payments 15,000 Final fee due at maturity in 2019 1,200 Total principal and final fee payments 16,200 Unamortized discount and debt issuance costs (1,664 ) Loan payable, long term $ 14,536 The obligation includes a final fee of $1,200,000 , representing 8% of the term loan funded, which accretes over the life of the loan as interest expense. The Company recorded interest expense related to the loan of $699,000 for the year ended December 31, 2015. Oxford Finance and SVB Loan Agreement In November 2011, the Company entered into a loan and security agreement (the "Oxford and SVB Loan Agreement"), with Oxford Finance LLC and Silicon Valley Bank, or SVB, under which the Company borrowed $4,000,000 in November 2011, and $8,000,000 in April 2012. The interest rate, which was fixed at the closing of each tranche, equaled the three-month LIBOR plus 7.75% . The interest rates for the tranches under the Oxford and SVB Loan Agreement were 8.18% and 8.22% per annum. Payments were monthly in arrears and interest only until September 1, 2012, followed by equal monthly payments of principal and interest through June 2014, when the loan was repaid in full. In addition, a final payment equal to 8.25% of the aggregate amount drawn was due upon termination of the Oxford and SVB Loan Agreement, which was accreted as interest expense over the term of the loan using the effective-interest method, with the remaining balance charged to interest expense upon loan repayment. The loan principal balance, accrued interest and the final payment under the Oxford and SVB Loan Agreement totaling $4,454,000 were repaid in full in June 2014. During 2012 and 2011, in connection with the Oxford and SVB Loan Agreement, the Company issued warrants to Oxford Finance LLC and SVB to purchase 20,016 and 10,008 shares, respectively, of its Series C convertible preferred stock at an exercise price of $11.99 per share. The fair value of these warrants at the date of issuance was approximately $163,000 and $86,000 , respectively, and was recorded as a debt discount and was amortized as interest expense over the term of the loan using the effective-interest method, with the remaining balance charged to interest expense upon loan repayment. Immediately prior to the closing of the IPO, these warrants automatically converted into warrants exercisable for shares of common stock, resulting in the reclassification of the related preferred stock warrant liabilities to additional paid-in capital. As of December 31, 2015, these warrants remained outstanding and exercisable. The Company recorded interest expense related to the Oxford and SVB Loan Agreement of $397,000 and $1,037,000 for the years ended December 31, 2014 and 2013, respectively. Funding Agreement with The Wellcome Trust In March 2010, the Company entered into a Funding Agreement, referred to herein as the 2010 Wellcome Funding Agreement, with The Wellcome Trust Limited, a company registered in England and Wales, as trustee for The Wellcome Trust, which is referred to herein as the Trust. Under the 2010 Wellcome Funding Agreement, the Trust provided an unsecured convertible loan of $5,594,000 to the Company to progress its aminoglycoside program. In March 2013, the outstanding balance under the 2010 Wellcome Funding Agreement of $5,594,000 was converted into 583,162 shares of Series D convertible preferred stock at a conversion price that represented a 20% discount to the issue price. The 20% discount feature was recorded as a debt discount on the funding dates and accreted over the life of the debt up to the date of redemption. The Company recorded interest expense related to the 2010 Wellcome Funding Agreement of $153,000 for the year ended December 31, 2013. Convertible Notes Purchase Agreement In November 2012, the Company entered into a Note Purchase Agreement, referred to herein as the 2012 Bridge Loan Agreement, with a group of existing investors. Under the 2012 Bridge Loan Agreement, the investors severally agreed to purchase convertible promissory notes for a principal amount of up to $3,000,000 in aggregate. For value received, the Company agreed to pay to the investors the principal loan amount plus accrued interest calculated at a rate equal to 6% per annum. The Company recorded interest expense related to the 2012 Bridge Loan Agreement of $26,000 for the year ended December 31, 2013. On March 6, 2013, the investors under the 2012 Bridge Loan Agreement converted the entire outstanding notes amount plus accrued interest totaling $2,732,000 into 227,784 shares of the Company’s Series D convertible preferred stock at a conversion price of $11.99 per share, which was the issuance price of Series D convertible preferred stock.

Stockholders' Equity and Conver

Stockholders' Equity and Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2015
Temporary Equity Disclosure [Abstract]
Stock holders' Equity and Convertible Preferred Stock	Stockholders' Equity and Convertible Preferred Stock Stockholders' Equity On April 7, 2015, the Company entered into a Sales Agreement (the “Sales Agreement”) with Cowen and Company, LLC (“Cowen”), pursuant to which the Company may issue and sell shares of its common stock having aggregate sales proceeds of up to $30.0 million from time to time through an ATM equity program under which Cowen acts as sales agent. In September 2015, the Company sold 197,838 shares of common stock under the Sales Agreement, at a weighted-average price of approximately $7.05 per share for gross proceeds of $1.4 million and net proceeds of $1.3 million after deducting the sales commissions and offering expenses. As of December 31, 2015, $28.6 million of common stock remained available to be sold under the Sales Agreement, subject to certain conditions specified therein. Convertible Preferred Stock Immediately prior to the completion of the Company’s IPO, all of the outstanding shares of convertible preferred stock automatically converted into 10,386,894 shares of common stock. Each share of Series A, B, C, and D convertible preferred stock converted into common shares at a conversion rate of approximately 1.15 , 1.33 , 1.00 and 1.00 shares of common stock, respectively. In May 2013, the Company completed the first of two tranches of its Series D round of financing. The majority of the first tranche was received in March 2013 and the Company issued 1,110,252 shares of Series D convertible preferred stock at $11.99 per share to existing investors in exchange for cash proceeds of $10,581,000 and conversion of outstanding loans and accrued interest in the aggregate of $2,732,000 under the 2012 Bridge Loan Agreement. The remaining amount of the first tranche was received in May 2013 from a new investor for additional cash proceeds of $1,778,000 for the issuance of 148,289 shares at a price of $11.99 per share. The second tranche was closed in November 2013. The Company issued 834,031 additional shares of Series D convertible preferred stock at $11.99 per share for gross cash proceeds of $10,000,000 . Warrants In connection with the Oxford and SVB Loan Agreement described in Note 8, the Company issued warrants to Oxford Finance LLC and SVB during 2012 and 2011. As of December 31, 2015, the following warrants to purchase shares of common stock were outstanding and exercisable: Warrant Holder Issue Date In Connection With Warrant to Shares Purchase Expiration Date Oxford Finance LLC 4/30/2012 Loan agreement Common stock 11,676 $ 11.99 11/1/2021 SVB 4/30/2012 Loan agreement Common stock 8,340 $ 11.99 11/1/2021 Oxford Finance LLC 11/1/2011 Loan agreement Common stock 5,838 $ 11.99 11/1/2021 SVB 11/1/2011 Loan agreement Common stock 4,170 $ 11.99 11/1/2021 Total 30,024 In January 2014, a common stock warrant was exercised for 909 shares with an exercise price of $1.54 per share.

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Incentive Plans	Equity Incentive Plans 2014 Plan In February 2014, the Company’s stockholders approved the 2014 Equity Incentive Award Plan (the "2014 Plan"), which became effective as of March 11, 2014. Under the 2014 Plan, the Company may grant incentive stock options ("ISOs"), nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units awards ("RSUs") and other stock-based awards for the purchase of that number of shares of common stock. Effective January 1, 2015, the compensation committee of the board of directors approved an evergreen increase of 716,285 shares that may be granted in accordance with the terms of the 2014 Plan. As of December 31, 2015, 637,037 shares were available for future issuance under the 2014 Plan. Under the 2014 Plan, the terms of stock award agreements, including vesting requirements, are determined by the board of directors, subject to the provisions of the 2014 Plan. Options granted by the Company typically vest over a four years period and the exercise price may not be less than fair market value on the date of grant. Certain of the options are subject to acceleration of vesting in the event of certain change of control transactions. Options granted under the 2014 Plan expire no later than 10 years from the date of grant. 2014 Employment Commencement Incentive Plan In December 2014, the Company adopted a 2014 Employment Commencement Incentive Plan (the "Inducement Plan"). The Inducement Plan is designed to comply with the inducement exemption contained in Nasdaq’s Rule 5635(c)(4), which provides for the grant of non-qualified stock options, restricted stock units, restricted stock awards, performance awards, dividend equivalents, deferred stock awards, deferred stock units, stock payment and stock appreciation rights to a person not previously an employee or director of the Company, or following a bona fide period of non-employment, as an inducement material to the individual’s entering into employment with the Company. The number of shares of common stock initially reserved for issuance under the Inducement Plan was 650,000 shares. As of December 31, 2015, 256,425 shares were available for issuance under the Inducement Plan. 2014 Employee Stock Purchase Plan In February 2014, the Company’s stockholders approved the 2014 Employee Stock Purchase Plan (the “ESPP”), which became effective as of March 11, 2014. The number of shares of common stock initially reserved for issuance under the ESPP was 145,454 shares. Effective January 1, 2015, the board of directors approved an evergreen increase of 179,071 shares that may be granted in accordance with the terms of the ESPP. As of December 31, 2015, 79,537 shares of common stock have been issued to employees participating in the ESPP, and 244,988 shares were available for issuance under the ESPP. Amended and Restated 2003 Stock Plan The Company’s Amended and Restated 2003 Stock Plan, referred to herein as the 2003 Plan, provided for the granting of incentive and non-statutory stock options to employees, directors and consultants at the discretion of the board of directors. The Company granted options under its 2003 Plan until January 2014 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2003 Plan. Options granted under the 2003 Plan expire no later than 10 years from the date of grant. Options granted under the 2003 Plan vest over periods determined by the board of directors, generally over four years. In connection with the Board of Directors and stockholders approval of the 2014 Plan, all remaining shares available for future awards under the 2003 Plan were transferred to the 2014 Plan, and the 2003 Plan was terminated as to future awards. As of December 31, 2015, a total of 974,196 shares of common stock are subject to options outstanding under the 2003 plan, which shares will become available under the 2014 Plan to the extent the options are forfeited or lapse unexercised. Total stock-based compensation recognized in the Company’s consolidated statements of operations for the years ended December 31, 2015, 2014 and 2013, was classified as follows (in thousands): Year Ended December 31, 2015 2014 2013 Research and development $ 1,404 $ 570 $ 351 General and administrative 1,579 1,480 702 Total $ 2,983 $ 2,050 $ 1,053 A summary of stock option activity is as follows: Outstanding Options Shares Number of Weighted-Average Weighted-Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Balance, January 1, 2013 47,762 1,340,433 $ 5.72 Additional shares reserved 163,636 — Options granted (168,231 ) 168,231 $ 5.28 Options exercised — (19,004 ) $ 3.65 $ 65 Options forfeited 75,673 (75,673 ) $ 6.21 Option expired 8,437 (8,437 ) $ 5.55 Balance, December 31, 2013 127,277 1,405,550 $ 5.68 Additional shares reserved 1,190,908 — Shares reserved for the 2014 Employment Commencement Incentive Plan 650,000 — Options granted (876,163 ) 876,163 $ 10.15 RSUs granted (168,200 ) — Options exercised — (208,693 ) $ 3.38 $ 1,704 Options forfeited 187,648 (187,648 ) $ 6.29 Balance, December 31, 2014 1,111,470 1,885,372 $ 7.95 Additional shares reserved 716,285 — Options granted (929,100 ) 929,100 $ 7.95 Options exercised — (190,128 ) $ 5.54 $ 923 Options forfeited 237,007 (237,007 ) $ 10.22 RSUs granted (291,525 ) — RSUs cancelled 49,325 — Balance, December 31, 2015 893,462 2,387,337 $ 7.92 7.61 $ 293 At December 31, 2015: Vested and exercisable 981,797 $ 7.64 6.30 $ 249 Vested and expected to vest 2,238,972 $ 7.86 7.67 $ 292 The following table summarizes information about stock options outstanding as of December 31, 2015: Options Outstanding Vested and Exercisable Exercise Price Number of Options Weighted-Average Number of Options Weighted-Average $1.65 - $4.73 240,519 5.94 204,615 $ 4.55 $5.53- $5.86 324,250 9.50 23,888 $ 5.53 $6.60 34,620 7.74 19,952 $ 6.60 $6.93 241,162 5.33 218,890 $ 6.93 $6.99- $7.08 277,650 9.69 12,277 $ 6.99 $7.26 286,535 6.16 175,681 $ 7.26 $8.04- $9.21 334,800 8.78 93,521 $ 8.45 $9.24- $10.44 336,252 8.27 100,395 $ 9.77 $11.78 - $12.22 257,189 5.73 109,768 $ 11.99 $14.89 54,360 8.48 22,810 $ 14.89 2,387,337 7.61 981,797 $ 7.64 Stock Options Granted to Employees and Non-Employee Directors During the years ended December 31, 2015, 2014 and 2013, the Company granted stock options to employees and directors to purchase 929,100 , 876,163 and 168,231 shares, respectively, of common stock under the stock plans with a weighted-average estimated grant-date fair value of $5.02 , $6.41 and $3.74 per share, respectively. As of December 31, 2015, there were unrecognized compensation costs of $5,922,000 related to outstanding employee and non-employee director stock options, which are expected to be recognized over a weighted-average period of 3.0 years. The Company estimated the fair value of stock options using the Black-Scholes option valuation model for options with time-based vesting terms. The Black-Scholes model requires the input of subjective assumptions, including (a) the expected term of the award, (b) the expected stock price volatility, (c) the risk-free interest rate and (d) expected dividends. The estimated fair value of these employee stock options is being amortized on a straight-line basis over the requisite service period of the awards. The fair value of the employee stock options was estimated using the following weighted-average assumptions: Year Ended 2015 2014 2013 Expected term 5.4–6.0 years 5.3–6.1 years 5.4–6.1 years Expected volatility 65%–75% 67%–77% 68%–69% Risk-free interest rate 1.5%–1.9% 1.7%–2.0% 1.2%–1.7% Expected dividend yield 0% 0% 0% The Company has opted to use the “simplified method” for estimating the expected term of options, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option. Prior to the Company's IPO in March 2014, due to the Company’s limited operating history and company specific stock price volatility data, the Company based its estimate of expected volatility on the historical price volatility of a group of similar companies that are publicly traded. Beginning in 2014 the Company began to include the historical price volatility of its own stock, along with data for the group of similar companies, to estimate expected volatility. When selecting these public companies to use in estimating its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, stages of clinical development, risk profiles, position within the industry and with historical share price information sufficient to meet the expected life of the stock-based awards. The risk-free rate assumption is based on the U.S. Treasury instruments with maturities similar to the expected term of the Company’s stock options. The expected dividend assumption is based on the Company’s history of not paying dividends and its expectation that it will not declare dividends for the foreseeable future. During the years ended December 31, 2014 and 2013, the Company issued 168,977 and 23,770 options to purchase common stock, respectively, that vests upon the achievement of market-based common stock price targets. The fair value was estimated at the grant date using a Monte-Carlo simulation model. The Monte-Carlo simulation model requires the use of a range of assumptions. The range of risk-free interest rates was 2.2% to 2.8% , expected volatility rates ranged from 60% to 70% and the dividend rate was 0% . The expected life assumption is not used in the Monte-Carlo simulation model, but the output of the model indicated an expected life of 2.9 to 6.3 years. The associated stock-based compensation expense is being recognized on a graded basis over the implicit service period derived from that simulation model. Forfeitures of unvested grants are estimated at the time of the grant. The estimated rate of forfeitures is re-evaluated periodically and adjusted as necessary. Ultimately, the actual expense recognized will be only for those options that vest. Restricted Stock Units Granted to Employees and Non-Employee Directors During the years ended December 31, 2015 and 2014, the Company granted restricted stock units ("RSUs") to employees to purchase 291,525 and 168,200 shares of common stock, respectively, under the stock plans with a weighted-average estimated grant-date fair value of $7.76 and $9.33 per share, respectively. RSUs generally vest annually over a 4 -year service period and vesting is contingent on continued service. As of December 31, 2015, there were unrecognized compensation costs of $2,682,000 related to outstanding RSUs, which are expected to be recognized over a weighted-average period of 3.29 years. A summary of RSU activity is as follows: RSUs Outstanding Number of Shares Weighted-Average Grant Date Fair Value per Share Aggregate Intrinsic Value (in thousands) Balance, December 31, 2013 — $ — RSUs granted 168,200 $ 9.33 Balance, December 31, 2014 168,200 $ 9.33 $ 2,195 RSUs granted 291,525 $ 7.76 RSUs released (38,376 ) $ 9.42 RSUs cancelled (49,325 ) $ 9.80 Balance, December 31, 2015 372,024 $ 8.02 $ 2,135

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2015, 2014 and 2013 is as follows: Year ended December 31, 2015 2014 2013 Statutory tax rate 34.00 % 34.00 % 34.00 % State taxes, net of federal benefits (3.62 )% 5.04 % 7.10 % Stock-based compensation (1.20 )% (0.76 )% (0.81 )% Credits 3.30 % 3.21 % 7.65 % Other (0.54 )% (1.74 )% (0.01 )% Valuation allowance (31.94 )% (39.75 )% (47.93 )% Effective tax rate — % — % — % The tax effects of temporary differences and carryforwards that give rise to our deferred tax assets are as follows (in thousands): December 31, 2015 2014 Deferred tax assets: Net operating loss carry forwards $ 57,558 $ 51,039 Research and development credit 8,531 7,680 Intangible assets 1,994 2,293 Depreciation 195 120 Other 2,396 1,567 Gross Deferred tax assets 70,674 62,699 Less: valuation allowance (70,674 ) (62,699 ) Net deferred tax assets $ — $ — 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 increased by $7,975,000 , $7,950,000 and $6,295,000 during the years ended December 31, 2015, 2014 and 2013, respectively. The Company had federal and state net operating loss carryforwards of approximately $153,649,000 and $98,459,000 , respectively, at December 31, 2015. The federal and state net operating loss carryforwards are available to reduce future taxable income, if any. If not utilized, the federal and state operating loss carryforwards will begin to expire in various amounts beginning 2023 and 2016 , respectively. The Company also had federal and state research and development credit carryforwards of approximately $6,915,000 and $4,126,000 , respectively, at December 31, 2015. The federal research and development credits will begin to expire in 2025 . The state research and development credits can be carried forward indefinitely. Utilization of the net operating loss and research and development credits carryforwards may be subject to an annual limitation due to the ownership change limitations provided by the Internal Revenue Code of 1986 and similar state provisions. The annual limitation may result in the expiration of the net operating loss and research and development credits before utilization. The Company files income tax returns in the U.S. federal jurisdiction and various state jurisdictions. The Company is subject to U.S. federal and state income tax examinations by tax authorities for tax years from 2003 due to net operating losses and tax credits that are being carried forward for tax purposes. The Company recognizes the financial statements effects of a tax position when it is more likely than not, based on technical merits, that the position will be sustained upon examination. A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands): December 31, 2015 2014 2013 Balance at beginning of year $ — $ — $ — Increase related to current year tax provision 162 — — Increase related to prior year tax provision 795 — — Balance at end of year $ 957 $ — $ — The unrecognized tax benefits, if recognized and in absence of full valuation allowance, would impact the income tax provision by $820,000 and $678,000 as of December 31, 2015 and 2014. Given the Company’s valuation allowance, the uncertain tax positions would not impact the effective tax rates. The Company has elected to include interest and penalties as a component of tax expense. There was no interest or penalties accrued related to uncertain tax positions as of December 31, 2015.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plan	Employee Benefit Plan In 2003, the Company adopted a 401(k) plan for its employees whereby eligible employees may contribute up to 100% of their compensation, on a pretax basis, subject to the maximum amount permitted by the Internal Revenue Code. In December 2010, the Company approved a plan to provide matching contributions equal to 50% of employees’ contributions, up to 6% of annual earnings, starting in January 2011. In December 2015, the Company has changed the plan to increase its 401(k) match to 50% of employees' contributions, up to 8% of annual earnings, starting in January 2016. Company's contributions were $255,000 , $184,000 and $152,000 for the years ended December 31, 2015, 2014 and 2013, respectively.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related-Party Transactions	Related-Party Transactions In 2010, the Company entered into the 2010 Wellcome Funding Agreement with the Trust, one of the Company’s preferred stockholders. As of December 31, 2012, the Company had received $5,594,000 under the 2010 Wellcome Funding Agreement, and recorded the amount as a related-party convertible loan payable. The loan was convertible, at the holder’s option, into the Company’s next round of preferred stock. In March 2013, the outstanding balance of the 2010 Wellcome Funding Agreement, $5,594,000 , was converted into Series D convertible preferred stock at a conversion price that represented a 20% discount to the issue price. Refer to Note 8, “Borrowings.”

Restructuring Charges

Restructuring Charges	12 Months Ended
	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Restructuring Charges	Restructuring Charges For the year ended December 31, 2013, as a result of the Company ceasing to use certain areas of its leased property, additional restructuring charges of $319,000 were recorded relating to the impairment of certain leasehold improvements of $194,000 , net of cash from asset disposal of $2,000 , and the recognition of the remaining lease obligation on the subleased ceased-used property of $125,000 in general and administrative expenses. The Company paid accrued facility charges of $274,000 , net of cash received from the Company’s subtenant, through March 2014.

Selected Unaudited Quarterly Fi

Selected Unaudited Quarterly Financial Data	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Selected Unaudited Quarterly Financial Data	Selected Unaudited Quarterly Financial Data The following tables show a summary of the Company’s unaudited quarterly financial data for each of the four quarters of 2015 and 2014 (in thousands, except per share amounts): Three Months Ended December 31, 2015 September 30, 2015 June 30, 2015 March 31, 2015 Contract revenue $ 4,664 $ 4,476 $ 12,041 $ 4,880 Operating expenses $ 15,548 $ 13,006 $ 12,970 $ 11,110 Interest and other income (expense), net $ (382 ) $ (232 ) $ 43 $ 51 Net loss $ (11,266 ) $ (8,762 ) $ (886 ) $ (6,179 ) Basic and diluted net loss per common share (1) $ (0.61 ) $ (0.48 ) $ (0.05 ) $ (0.34 ) Three Months Ended December 31, 2014 September 30, 2014 June 30, 2014 March 31, 2014 Contract revenue $ 4,259 $ 4,520 $ 5,203 $ 5,988 Operating expenses $ 9,140 $ 12,853 $ 8,541 $ 9,222 Interest and other income (expense), net $ 27 $ 21 $ (217 ) $ (221 ) Net loss $ (4,854 ) $ (8,312 ) $ (3,555 ) $ (3,455 ) Basic and diluted net loss per common share (1) $ (0.27 ) $ (0.47 ) $ (0.20 ) $ (1.00 ) (1) Basic and diluted net loss per common share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted net loss per common share.

Summary of Significant Accoun23

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The accompanying financial statements have been prepared in accordance with U.S. GAAP. The preparation of financial statements in conformity with U.S. GAAP requires management to make judgments, assumptions and estimates that affect the reported amounts of assets, liabilities, revenues and expenses and related disclosures of contingent liabilities. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of derivative liabilities, common stock and stock-based awards and income taxes. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of the Company’s financial instruments, including cash and cash equivalents, contracts receivable, prepaid and other current assets, accounts payable, accrued liabilities, and other current liabilities approximate fair value due to their short-term maturities. Short-term investments consist of available-for-sale securities as of December 31, 2015 and are carried at fair value. Based upon the borrowing rates currently available to the Company for loans with similar terms, the Company believes the carrying amounts of the loan payable and the derivative liability also represent fair values.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash equivalents include only securities having an original maturity of three months or less at the time of purchase.
Short-term Investments	Short-term Investments Short-term investments consist of debt securities with maturities greater than three months, but less than one year from the date of acquisition, and are classified as available for sale. Short-term investments are carried at fair value. Unrealized gains and losses on available-for-sale securities are excluded from earnings and are reported as a component of net unrealized losses on available-for-sale securities in the Company's consolidated statements of comprehensive loss. The amortized cost of debt securities reflects amortization of purchase premiums and accretion of purchase discounts to date, which is included in interest income. The Company reviews all of its marketable securities on a regular basis to evaluate whether any security has experienced an other-than-temporary decline in fair value.
Restricted Cash	Restricted Cash At December 31, 2015 and 2014, the Company had long-term restricted cash of $127,000 . The restricted cash, which consists of a money market account with one of the Company’s financial institutions, serves as collateral for a letter of credit provided as a security deposit under the Company’s facility lease. The facility lease expires on April 14, 2017 .
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. The Company has one operating segment.
Customer Concentration	Customer Concentration For the years ended December 31, 2015, 2014 and 2013, all of the Company’s revenue has been generated solely from funding pursuant to U.S. government contracts, and accordingly all contracts receivable relate to funding from U.S. government contracts.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to a significant concentration of credit risk consist of cash, cash equivalents and short-term investments. Cash and cash equivalents are deposited in checking and money market accounts at one financial institution, which at times, may exceed federally insured limits. Management believes that the financial institution is financially sound, and, accordingly, minimal credit risk exists with respect to this financial institution. Our investment policy limits investments to certain types of debt securities issued by the U.S. government, its agencies and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The Company is exposed to credit risk in the event of default by the institutions holding its cash and cash equivalents or issuing the debt securities.
Contracts Receivable	Contracts Receivable Contracts receivable represent amounts owed to the Company under certain government contracts.
Property and Equipment, Net	Property and Equipment, Net Property and equipment consists of office equipment, laboratory equipment, and leasehold improvements and is stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over their estimated useful lives or the remaining lease term, whichever is shorter. Maintenance and repair costs are recorded as a component of operating expenses in the Company’s consolidated statement of operations when incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. If indicators of impairment exist, an impairment loss would be recognized when the estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment charge is determined based upon the excess of the carrying value of the asset over its estimated fair value, with estimated fair value determined based upon an estimate of discounted future cash flows or other appropriate measures of estimated fair value.
Convertible Preferred Stock Warrant Liabilities	Convertible Preferred Stock Warrant Liabilities The Company accounted for its Series A and Series C convertible preferred stock warrants as freestanding warrants for shares that are puttable or redeemable. At December 31, 2013, these warrants were classified as liabilities on the consolidated balance sheet at their estimated fair value. At the end of each reporting period, changes in estimated fair value during the period were recorded as a component of other income, net. At the time of the IPO, the warrants to purchase preferred stock were converted into warrants to purchase common stock, which are no longer subject to remeasurement, and the preferred stock warrant liability was reclassified to additional paid-in capital at its then fair value.
Stock-Based Compensation	Stock-Based Compensation The Company measures and recognizes the compensation expense for all stock-based awards made to employees and directors, including employee stock options, stock grants and employee stock purchases related to the Employee Stock Purchase Plan (“ESPP”) based on estimated fair values. The Company uses the Black-Scholes option-pricing valuation model to estimate the grant-date fair value of stock option and ESPP awards with time-based vesting terms. The determination of fair value for stock-based awards on the date of grant using an option-pricing model requires management to make certain assumptions regarding a number of complex and subjective variables. The fair value of restricted stock unit (“RSU”) awards with time-based vesting terms is based on the grant date share price. The Company recognizes stock-based compensation cost over the award’s requisite service period on a straight-line basis for time-based awards and on a graded basis for awards that are contingent on the achievement of market-based conditions. The Company records stock-based compensation expense, net of the estimated impact of forfeited awards. As such, the Company recognizes stock-based compensation expense only for those stock-based awards that are expected to vest over their requisite service period, based on the vesting provisions of the individual underlying grants. During 2014 and 2013, the Company issued stock-based option awards with market-based conditions that vest upon achievement of certain market price thresholds of the Company’s common stock. The estimated fair value for market-based stock option awards is determined using a lattice valuation model with a Monte-Carlo simulation. The model takes into consideration the historical volatility of the Company’s stock and the risk-free interest rate at the date of grant. In addition, the model is used to estimate the derived service period for the awards. The derived service period is the estimated period of time that would be required to satisfy the market condition, assuming the market condition will be satisfied. Stock-based compensation expense is recognized over the implicit service period derived from the Monte-Carlo simulation model, as applicable, but is accelerated if the market condition is achieved earlier than estimated. For non-employee stock-based awards, the measurement date on which the estimated fair value of the stock-based award is calculated is equal to the earlier of (i) the date at which a commitment for performance by the counterparty to earn the equity instrument is reached or (ii) the date at which the counterparty’s performance is complete. The Company recognizes stock-based compensation expense for the estimated fair value of the vested portion of non-employee awards.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when: (i) evidence of an arrangement exists, (ii) fees are fixed or determinable, (iii) services have been delivered, and (iv) collectability is reasonably assured. The Company currently generates revenue entirely from government contracts. Government contracts are agreements that provide the Company with payments for certain types of expenditures in return for research and development activities over a contractually defined period. Revenue from government contracts is recognized in the period during which the related costs are incurred and the related services are rendered, provided that the applicable conditions under the government contracts have been met. Costs of contract revenue are recorded as a component of operating expenses in the Company's consolidated statements of operations. Funds received from third parties under contract arrangements are recorded as revenue if the Company is deemed to be the principal participant in the contract arrangements because the activities under the contracts are part of the Company’s development programs. If the Company is not the principal participant, the funds from contracts are recorded as a reduction to research and development expense. Contracts funds received are not refundable and are recognized when the related qualified research and development costs are incurred and when there is reasonable assurance that the funds will be received. Funds billed and received in advance are recorded as deferred revenue.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses include certain payroll and personnel expenses; laboratory supplies; consulting costs; external contract research and development expenses; and allocated overhead, including rent, equipment depreciation and utilities, and relate to both Company-sponsored programs as well as costs incurred pursuant to collaboration agreements and government contracts. Nonrefundable advance payments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized and recognized as an expense as the goods are delivered or the related services are performed. The Company estimates preclinical study and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on its behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the receipt of the related services are recorded as prepaid expenses until the services are rendered.
Leases	Leases The Company has entered into lease agreements for its laboratory and office facilities. These leases qualify as and are accounted for as operating leases. Rent expense is recognized on a straight-line basis over the term of the lease and, accordingly, the Company records the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Incentives granted under the Company’s facilities leases, including allowances to fund leasehold improvements and rent holidays, are capitalized and are recognized as reductions to rental expense on a straight-line basis over the term of the lease.
Income Taxes	Income Taxes The Company uses the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits. The tax benefit recognized in the financial statements for a particular tax position is the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company's policy is to recognize interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense.
Net Loss and Per Share	Net Loss and Per Share Basic net loss per common share is computed by dividing the net loss by the weighted-average number of common shares outstanding during the period. Diluted net loss per common share is computed by dividing the net loss by the weighted-average number of common shares and dilutive common share equivalents outstanding during the period. Because the Company has reported a net loss for the years ended December 31, 2015, 2014 and 2013, diluted net loss per common share is the same as basic net loss per common share for those periods. Effective as of the completion of the IPO, all of the Company’s preferred stock was converted to common stock. For purposes of calculating net loss per common share for the year ended December 31, 2014, the preferred stock converted to common stock was included in the net loss per common share calculation on a post-conversion basis based on the conversion date.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition . This ASU is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. The ASU's effective date is for interim and annual periods beginning after December 15, 2017. Adoption of the ASU is either retrospective to each prior period presented or retrospective with a cumulative adjustment to retained earnings or accumulated deficit as of the adoption date. Early adoption is permitted. The Company is assessing the potential effects of this ASU on its consolidated financial statements. In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern (Topic 205-40), Going Concern . This ASU introduces an explicit requirement for management to assess if there is substantial doubt about an entity's ability to continue as a going concern, and to provide related footnote disclosures in certain circumstances. In connection with each annual and interim period, management must assess if there is substantial doubt about an entity's ability to continue as a going concern within one year after the issuance date. Disclosures are required if conditions give rise to substantial doubt. ASU 2014-15 is effective for all entities in the first annual period ending after December 15, 2016. The Company is currently assessing the potential effects of this ASU on its consolidated financial statements. In January 2015, the FASB issued ASU No. 2015-01, Income Statement - Extraordinary and Unusual Items (Subtopic 225-20) - Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items . This guidance eliminates from GAAP the concept of extraordinary items and is effective for annual reporting periods, including interim reporting periods, beginning after December 15, 2015, and is applicable to the Company's fiscal year beginning January 1, 2016. Early adoption is permitted. The Company does not anticipate it will have a material impact to its consolidated financial statements. In April 2015, the FASB issued ASU No. 2015-03, Simplifying the Presentation of Debt Issuance Costs , to require debt issuance costs to be presented as an offset against debt outstanding. The ASU is effective for interim and annual periods beginning after December 15, 2015 and early adoption is permitted. Application is retrospective to each prior period presented. The Company elected to adopt this standard during the twelve-months ended December 31, 2015. As a result, all issuance costs associated with the Company’s loan payable issued during the twelve-months ended December 31, 2015 have been classified as a debt discount. The adoption of this standard did not impact the Company’s consolidated balance sheet as of December 31, 2014, or the consolidated statements of operations, comprehensive loss or cash flows for any period presented. In November 2015, the FASB issued ASU No. 2015-17, Income Taxes (Topic 740) - Balance Sheet Classification of Deferred Taxes . This guidance simplifies the presentation of deferred income taxes in a classified balance sheet to require that deferred tax liabilities and assets be classified as noncurrent and is effective for annual reporting periods, including interim reporting periods, beginning after December 15, 2016, and is applicable to the Company's fiscal year beginning January 1, 2017. Early adoption is permitted. The Company does not anticipate it will have a material impact to its consolidated financial statements.

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Schedule of Weighted Average Number of Shares	The following table sets forth the computation of the basic and diluted net loss per share during the years ended December 31, 2015, 2014 and 2013 (in thousands, except share and per share amounts): Year Ended December 31, 2015 2014 2013 Net loss $ (27,093 ) $ (20,176 ) $ (13,112 ) Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share 18,147,986 14,210,098 387,547 Basic and diluted net loss per common share $ (1.49 ) $ (1.42 ) $ (33.83 )
Schedule of Potentially Dilutive Securities Outstanding Excluded from the Computations of Diluted Weighted-Average Shares Outstanding	The following potentially dilutive securities outstanding have been excluded from the computations of diluted weighted-average shares outstanding because such securities have an anti-dilutive impact due to losses reported (in common stock equivalent shares): December 31, 2015 2014 2013 Convertible preferred stock — — 10,386,894 Warrants to purchase convertible preferred stock — — 40,454 Options to purchase common stock 2,387,337 1,885,372 1,405,550 Restricted stock units 372,024 168,200 — Warrants to purchase common stock 30,024 40,454 909

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Financial Assets and Liabilities Measured and Recognized at Fair Value	Financial assets and liabilities measured and recognized at fair value on a recurring basis were as follows (in thousands): As of December 31, 2015: Amortized Unrealized Unrealized Fair Value Assets Cash $ 1,013 $ — $ — $ 1,013 Level 1: Restricted cash 127 — — 127 Money market funds 19,274 — — 19,274 Subtotal 19,401 — — 19,401 Level 2: Corporate debt securities 34,490 — (47 ) 34,443 Commercial paper 1,997 — — 1,997 U.S. Treasury bills 2,005 — (1 ) 2,004 Subtotal 38,492 — (48 ) 38,444 Total $ 58,906 $ — $ (48 ) $ 58,858 Reported as: Cash and cash equivalents $ 20,287 Short-term investments $ 38,444 Restricted cash $ 127 Liabilities Level 3: Derivative liability $ 375 As of December 31, 2014: Amortized Unrealized Unrealized Fair Value Assets Cash $ 620 $ — $ — $ 620 Level 1: Restricted cash 127 — — 127 Money market funds 18,261 — — 18,261 Subtotal 18,388 — — 18,388 Level 2: Corporate debt securities 44,830 — (32 ) 44,798 Total $ 63,838 $ — $ (32 ) $ 63,806 Reported as: Cash and cash equivalents $ 18,881 Short-term investments $ 44,798 Restricted cash $ 127
Activity in Preferred Stock Warrant Liability	The following table provides a summary of changes in the estimated fair value of the Company’s liabilities measured at estimated fair value using significant Level 3 inputs for the years ended 2015, 2014 and 2013 (in thousands): Estimated Estimated Balance at December 31, 2012 $ 237 $ 1,398 Change in estimated fair value of convertible preferred stock warrant liabilities included in other income, net 7 — Extinguishment of derivative liability — (1,398 ) Balance at December 31, 2013 244 — Change in estimated fair value of convertible preferred stock warrant liabilities included in other income, net 42 — Reclassification of warrant liability to additional paid-in capital upon conversion of warrant to purchase convertible preferred stock to warrant to purchase common stock (286 ) — Balance at December 31, 2014 — — Issuance of Level 3 derivative liability — 356 Increase in estimated fair value — 19 Balance at December 31, 2015 $ — $ 375
Fair Value Measurements, Valuation Techniques	The fair value of the convertible preferred stock warrant liabilities was estimated to be $244,000 as of December 31, 2013 using the following assumptions: Year Ended December 31, 2013 Preferred stock fair value per share $10.89–$12.43 Volatility 65%–68% Risk-free interest rate 0.2%–2.6% Remaining contractual term (in years) 1.2–7.8 Dividend yield 0%

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Property and Equipment	Property and equipment consisted of the following (in thousands): December 31, 2015 2014 Office equipment $ 1,144 $ 1,033 Laboratory equipment 3,161 2,932 Leasehold improvements 1,072 1,000 5,377 4,965 Less: accumulated depreciation and amortization (4,472 ) (4,240 ) Property and equipment, net $ 905 $ 725
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): December 31, 2015 2014 Accrued clinical and development expenses $ 2,869 $ 1,618 Payroll and related bonus expenses 1,615 1,171 Other 443 477 $ 4,927 $ 3,266
Other Long-term Liabilities	Other long-term liabilities consisted of the following (in thousands): December 31, 2015 2014 Derivative liability $ 375 $ — Deferred rent 104 193 $ 479 $ 193

Commitments (Tables)

Commitments (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum payments under all noncancelable operating leases as of December 31, 2015, are as follows (in thousands): 2016 $ 776 2017 313 Total minimum lease payments $ 1,089

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Schedule of Maturities of Long-term Debt	Future principal debt payments on the loan payable are as follows (in thousands): December 31, 2015 2016 $ — 2017 5,000 2018 6,000 2019 4,000 Total principal payments 15,000 Final fee due at maturity in 2019 1,200 Total principal and final fee payments 16,200 Unamortized discount and debt issuance costs (1,664 ) Loan payable, long term $ 14,536

Stockholders' Equity and Conv29

Stockholders' Equity and Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2015
Temporary Equity Disclosure [Abstract]
Schedule of Stockholders' Equity Note, Warrants or Rights	As of December 31, 2015, the following warrants to purchase shares of common stock were outstanding and exercisable: Warrant Holder Issue Date In Connection With Warrant to Shares Purchase Expiration Date Oxford Finance LLC 4/30/2012 Loan agreement Common stock 11,676 $ 11.99 11/1/2021 SVB 4/30/2012 Loan agreement Common stock 8,340 $ 11.99 11/1/2021 Oxford Finance LLC 11/1/2011 Loan agreement Common stock 5,838 $ 11.99 11/1/2021 SVB 11/1/2011 Loan agreement Common stock 4,170 $ 11.99 11/1/2021 Total 30,024

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Stock-based Compensation Expense for Stock Options Granted to Employees and Non-employees	Total stock-based compensation recognized in the Company’s consolidated statements of operations for the years ended December 31, 2015, 2014 and 2013, was classified as follows (in thousands): Year Ended December 31, 2015 2014 2013 Research and development $ 1,404 $ 570 $ 351 General and administrative 1,579 1,480 702 Total $ 2,983 $ 2,050 $ 1,053
Summary of Stock Option Activity	A summary of stock option activity is as follows: Outstanding Options Shares Number of Weighted-Average Weighted-Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Balance, January 1, 2013 47,762 1,340,433 $ 5.72 Additional shares reserved 163,636 — Options granted (168,231 ) 168,231 $ 5.28 Options exercised — (19,004 ) $ 3.65 $ 65 Options forfeited 75,673 (75,673 ) $ 6.21 Option expired 8,437 (8,437 ) $ 5.55 Balance, December 31, 2013 127,277 1,405,550 $ 5.68 Additional shares reserved 1,190,908 — Shares reserved for the 2014 Employment Commencement Incentive Plan 650,000 — Options granted (876,163 ) 876,163 $ 10.15 RSUs granted (168,200 ) — Options exercised — (208,693 ) $ 3.38 $ 1,704 Options forfeited 187,648 (187,648 ) $ 6.29 Balance, December 31, 2014 1,111,470 1,885,372 $ 7.95 Additional shares reserved 716,285 — Options granted (929,100 ) 929,100 $ 7.95 Options exercised — (190,128 ) $ 5.54 $ 923 Options forfeited 237,007 (237,007 ) $ 10.22 RSUs granted (291,525 ) — RSUs cancelled 49,325 — Balance, December 31, 2015 893,462 2,387,337 $ 7.92 7.61 $ 293 At December 31, 2015: Vested and exercisable 981,797 $ 7.64 6.30 $ 249 Vested and expected to vest 2,238,972 $ 7.86 7.67 $ 292
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range	The following table summarizes information about stock options outstanding as of December 31, 2015: Options Outstanding Vested and Exercisable Exercise Price Number of Options Weighted-Average Number of Options Weighted-Average $1.65 - $4.73 240,519 5.94 204,615 $ 4.55 $5.53- $5.86 324,250 9.50 23,888 $ 5.53 $6.60 34,620 7.74 19,952 $ 6.60 $6.93 241,162 5.33 218,890 $ 6.93 $6.99- $7.08 277,650 9.69 12,277 $ 6.99 $7.26 286,535 6.16 175,681 $ 7.26 $8.04- $9.21 334,800 8.78 93,521 $ 8.45 $9.24- $10.44 336,252 8.27 100,395 $ 9.77 $11.78 - $12.22 257,189 5.73 109,768 $ 11.99 $14.89 54,360 8.48 22,810 $ 14.89 2,387,337 7.61 981,797 $ 7.64
Schedule of Estimated Grant Date Fair Value of Employee Stock Options Using Black-Scholes Valuation Model	The fair value of the employee stock options was estimated using the following weighted-average assumptions: Year Ended 2015 2014 2013 Expected term 5.4–6.0 years 5.3–6.1 years 5.4–6.1 years Expected volatility 65%–75% 67%–77% 68%–69% Risk-free interest rate 1.5%–1.9% 1.7%–2.0% 1.2%–1.7% Expected dividend yield 0% 0% 0%
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	A summary of RSU activity is as follows: RSUs Outstanding Number of Shares Weighted-Average Grant Date Fair Value per Share Aggregate Intrinsic Value (in thousands) Balance, December 31, 2013 — $ — RSUs granted 168,200 $ 9.33 Balance, December 31, 2014 168,200 $ 9.33 $ 2,195 RSUs granted 291,525 $ 7.76 RSUs released (38,376 ) $ 9.42 RSUs cancelled (49,325 ) $ 9.80 Balance, December 31, 2015 372,024 $ 8.02 $ 2,135

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2015, 2014 and 2013 is as follows: Year ended December 31, 2015 2014 2013 Statutory tax rate 34.00 % 34.00 % 34.00 % State taxes, net of federal benefits (3.62 )% 5.04 % 7.10 % Stock-based compensation (1.20 )% (0.76 )% (0.81 )% Credits 3.30 % 3.21 % 7.65 % Other (0.54 )% (1.74 )% (0.01 )% Valuation allowance (31.94 )% (39.75 )% (47.93 )% Effective tax rate — % — % — %
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences and carryforwards that give rise to our deferred tax assets are as follows (in thousands): December 31, 2015 2014 Deferred tax assets: Net operating loss carry forwards $ 57,558 $ 51,039 Research and development credit 8,531 7,680 Intangible assets 1,994 2,293 Depreciation 195 120 Other 2,396 1,567 Gross Deferred tax assets 70,674 62,699 Less: valuation allowance (70,674 ) (62,699 ) Net deferred tax assets $ — $ —
Summary of Unrecognized Tax Benefits	A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands): December 31, 2015 2014 2013 Balance at beginning of year $ — $ — $ — Increase related to current year tax provision 162 — — Increase related to prior year tax provision 795 — — Balance at end of year $ 957 $ — $ —

Selected Unaudited Quarterly 32

Selected Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following tables show a summary of the Company’s unaudited quarterly financial data for each of the four quarters of 2015 and 2014 (in thousands, except per share amounts): Three Months Ended December 31, 2015 September 30, 2015 June 30, 2015 March 31, 2015 Contract revenue $ 4,664 $ 4,476 $ 12,041 $ 4,880 Operating expenses $ 15,548 $ 13,006 $ 12,970 $ 11,110 Interest and other income (expense), net $ (382 ) $ (232 ) $ 43 $ 51 Net loss $ (11,266 ) $ (8,762 ) $ (886 ) $ (6,179 ) Basic and diluted net loss per common share (1) $ (0.61 ) $ (0.48 ) $ (0.05 ) $ (0.34 ) Three Months Ended December 31, 2014 September 30, 2014 June 30, 2014 March 31, 2014 Contract revenue $ 4,259 $ 4,520 $ 5,203 $ 5,988 Operating expenses $ 9,140 $ 12,853 $ 8,541 $ 9,222 Interest and other income (expense), net $ 27 $ 21 $ (217 ) $ (221 ) Net loss $ (4,854 ) $ (8,312 ) $ (3,555 ) $ (3,455 ) Basic and diluted net loss per common share (1) $ (0.27 ) $ (0.47 ) $ (0.20 ) $ (1.00 ) (1) Basic and diluted net loss per common share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted net loss per common share.

Organization and Basis of Pre33

Organization and Basis of Presentation and Consolidation - Additional Information (Detail) - USD ($)	Mar. 14, 2014	Sep. 30, 2015	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 07, 2015
Class of Stock [Line Items]
Equity instruments, value authorized							$ 150,000,000
Initial public offering, share issued			6,900,000
Proceeds from sales of common stock, gross				$ 1,400,000
Proceeds from issuance of common stock, net of commissions and other costs				1,300,000
Shares issued for underwriters' granted of their over-allotment option (in shares)			900,000
Proceeds from initial public offering, net of issuance costs			$ 73,900,000	0	$ 73,936,000	$ 0
Conversion of preferred stock to common stock upon initial public offering (in shares)	10,386,894		10,386,894
Cash, cash equivalents and short-term investments				58,700,000
Accumulated deficit				$ 175,993,000	$ 148,900,000
Common Stock
Class of Stock [Line Items]
Equity instruments, value authorized							$ 30,000,000
Initial public offering, share issued		197,838		197,838
Share price (in USD per share)		$ 7.05		$ 7.05
Proceeds from issuance of common stock, net of commissions and other costs		$ 1,300,000

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015USD ($)Segment	Dec. 31, 2013USD ($)	Dec. 31, 2014USD ($)
Property, Plant and Equipment [Line Items]
Restricted cash	$ 127,000		$ 127,000
Facility lease expiration date	Apr. 14, 2017
Number of operating segments | Segment	1
Allowance for doubtful accounts receivable	$ 0		$ 0
Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Impairment of Asset
Property, Plant and Equipment [Line Items]
Impairment charges		$ 194,000

Summary of Significant Accoun35

Summary of Significant Accounting Policies - Computation of the Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net loss	$ (11,266)	$ (8,762)	$ (886)	$ (6,179)	$ (4,854)	$ (8,312)	$ (3,555)	$ (3,455)	$ (27,093)	$ (20,176)	$ (13,112)
Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share									18,147,986	14,210,098	387,547
Basic and diluted net loss per common share (in dollars per share)									$ (1.49)	$ (1.42)	$ (33.83)
Accumulated Deficit
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net loss									$ (27,093)	$ (20,176)	$ (13,112)

Summary of Significant Accoun36

Summary of Significant Accounting Policies - Antidilutive Securities (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding	0	0	10,386,894
Warrants to purchase convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding	0	0	40,454
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding	2,387,337	1,885,372	1,405,550
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding	372,024	168,200	0
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding	30,024	40,454	909

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Measured and Recognized at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Restricted cash	$ 127	$ 127
Cash and cash equivalents	20,287	18,881	$ 10,738	$ 7,073
Short-term investments	38,444	44,798
Fair Value, Measurements, Recurring
Assets
Cash	1,013	620
Restricted cash	127	127
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(48)	(32)
Unrealized Gains	0
Total amortized cost	58,906	63,838
Total fair value	58,858	63,806
Cash and cash equivalents	20,287	18,881
Short-term investments	38,444	44,798
Fair Value, Measurements, Recurring | Level 1
Assets
Restricted cash	127	127
Money market funds	19,274	18,261
Subtotal	19,401	18,388
Fair Value, Measurements, Recurring | Level 2
Assets
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(48)
Amortized Cost	38,492
Fair Value	38,444
Fair Value, Measurements, Recurring | Level 3
Liabilities
Derivative Liability	375
Corporate Debt Securities | Fair Value, Measurements, Recurring | Level 2
Assets
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(47)	(32)
Amortized Cost	34,490	44,830
Fair Value	34,443	$ 44,798
Commercial Paper | Fair Value, Measurements, Recurring | Level 2
Assets
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	0
Amortized Cost	1,997
Fair Value	1,997
US Treasury Bill Securities | Fair Value, Measurements, Recurring | Level 2
Assets
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(1)
Amortized Cost	2,005
Fair Value	$ 2,004

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	Aug. 05, 2015	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2015	Jan. 31, 2014	Mar. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, fair value of success fee	$ 356,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Potential Payment			$ 1,000,000	$ 1,000,000
Fair Value Inputs, Discount Rate				13.00%
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Change in Percent Effecting Fair Value of Derivative Liability				5.00%
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Effect in Fair Value of Derivative Liability Due to Change in Percent of Approval Probability			30,000	$ 30,000
Fair Value of Derivative Liability, Benefit Conversion, Percentage				20.00%
Warrants to purchase common stock, exercise price (in USD per share)								$ 1.54
Reclassification of warrant liability to additional paid-in capital				$ 0	$ 286,000	$ 0
Convertible Preferred Stock Warrant Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Increase in estimated fair value recognized in net loss		$ 42,000			$ (42,000)	(7,000)
Reported Value Measurement | Convertible Preferred Stock Warrant Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible preferred stock warrant liabilities						$ 244,000
Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized loss position			36,500,000	$ 36,500,000
Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants to purchase common stock							40,454
Warrants to purchase common stock, exercise price (in USD per share)							$ 12.36
Estimated Fair Value of Derivative Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability									$ 1,398,000
Interest Expense | Derivative Financial Instruments, Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Increase (Decrease) in Fair Value			$ 19,000
Secured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Success Fee	1,000,000
Debt instrument, fair value of success fee	$ 356,000

Fair Value Measurements - Prefe

Fair Value Measurements - Preferred Stock Warrant Liability (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Convertible Preferred Stock Warrant Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Estimated Fair value, Beginning Balance		$ 0	$ 244	$ 237
Change in estimated fair value of convertible preferred stock warrant liabilities included in other income and expense, net	$ (42)		42	7
Reclassification of warrant liability to additional paid-in capital upon conversion of warrant to purchase convertible preferred stock to warrant to purchase common stock			(286)
Estimated fair value, Ending Balance		0	0	244
Estimated Fair Value of Derivative Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Estimated Fair value, Beginning Balance		0	0	1,398
Reclassification of warrant liability to additional paid-in capital upon conversion of warrant to purchase convertible preferred stock to warrant to purchase common stock				(1,398)
Estimated fair value, Ending Balance		375	$ 0	$ 0
Fair Value, Measurements, Recurring
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase in estimated fair value		19
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Issuance of Level 3 derivative liability		$ 356

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value of the Convertible Preferred Stock Warrant Liabilities (Details) - Convertible Preferred Stock Warrant	12 Months Ended
	Dec. 31, 2013$ / shares
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Dividend yield	0.00%
Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Preferred stock fair value per share (in dollars per share)	$ 10.89
Volatility (as percent)	65.00%
Risk-free interest rate	0.20%
Remaining contractual term (in years)	1 year 2 months 12 days
Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Preferred stock fair value per share (in dollars per share)	$ 12.43
Volatility (as percent)	68.00%
Risk-free interest rate	2.60%
Remaining contractual term (in years)	7 years 9 months 18 days

Balance Sheet Components (Detai

Balance Sheet Components (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 5,377	$ 4,965
Less: accumulated depreciation and amortization	(4,472)	(4,240)
Property and equipment, net	905	725
Office equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	1,144	1,033
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,161	2,932
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,072	$ 1,000

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Depreciation and amortization expense	$ 426	$ 358	$ 506

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued clinical and development expenses	$ 2,869	$ 1,618
Payroll and related bonus expenses	1,615	1,171
Other	443	477
Accrued liabilities, current	$ 4,927	$ 3,266

Balance Sheet Components - Othe

Balance Sheet Components - Other Long-term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Derivative liability	$ 375	$ 0
Deferred rent	104	193
Other Long-term Liabilities, Total	$ 479	$ 193

License and Collaboration Agr45

License and Collaboration Agreements - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2006	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense		$ 40,228,000	$ 30,110,000	$ 23,484,000
Isis Pharmaceuticals License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments for first commercialization product	$ 19,500,000
Milestone payments for second commercialization product	9,750,000
Aggregate additional milestone payments	20,000,000
Cumulative milestone compensation				$ 3,000,000
Cash payment of research and development expense			4,000,000
Milestone Payment Amount		$ 0	$ 0
Upfront License Fees | Isis Pharmaceuticals License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	$ 1,500,000
Upfront License Fees | Isis Pharmaceuticals License Agreement | Series A Convertible Preferred Stock
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Shares, issued	97,402
Shares issued, price per share (in USD per share)	$ 15.40

Government Contracts - Addition

Government Contracts - Additional Information (Detail) - USD ($)	1 Months Ended							8 Months Ended	12 Months Ended
	Jan. 31, 2016	Jul. 31, 2015	Jul. 31, 2014	Apr. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Aug. 31, 2010	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Contract revenue									$ 26,061,000	$ 19,970,000	$ 18,512,000
Contracts receivable								$ 5,039,000	5,039,000	5,234,000
Biomedical Advanced Research and Development Authority
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development contract				$ 103,808,000	$ 43,398,000		$ 27,600,000
Term of agreement							2 years
Increase in research and development contract				$ 60,410,000
Research and development, remaining available funding								26,731,000	26,731,000
Contract revenue									17,569,000	19,970,000	18,073,000
Contracts receivable								4,657,000	4,657,000	5,234,000
Defense Threat Reduction Agency
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Contract revenue								7,122,000
National Institute for Allergy and Infectious Diseases
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development contract		$ 1,500,000	$ 407,000			$ 22,188,000
Term of agreement			1 year			5 years
Contract revenue									1,370,000	0	$ 168,000
Contracts receivable								$ 382,000	$ 382,000	$ 0
Research and development grant, additional contract funding		$ 3,000,000
National Institute for Allergy and Infectious Diseases | Subsequent Event
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development grant, additional contract funding	$ 508,000

Commitments - Additional Inform

Commitments - Additional Information (Details) ft² in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2015USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Mar. 31, 2016USD ($)	May. 31, 2015ft²	Jun. 30, 2013ft²	Apr. 30, 2013ft²	Dec. 31, 2010USD ($)ft²
Property Subject to or Available for Operating Lease [Line Items]
Leasehold improvements, gross									$ 362,000
Rent expense		$ 526,000	$ 405,000	$ 673,000
Sublease income		0	97,000	291,000
Commitment, amount	$ 2,000,000
Research and development, current		944,000
Research and development		40,228,000	$ 30,110,000	$ 23,484,000
South San Francisco
Property Subject to or Available for Operating Lease [Line Items]
Operating leases, square footage | ft²							16		35
Sublease square footage | ft²						6		19
Restricted Cash
Property Subject to or Available for Operating Lease [Line Items]
Restricted cash		127,000
Scenario, Forecast
Property Subject to or Available for Operating Lease [Line Items]
Research and development, current					$ 500,000
Isis Pharmaceuticals License Agreement [Member]
Property Subject to or Available for Operating Lease [Line Items]
Research and development		$ 56,000

Commitments - Schedule of Futur

Commitments - Schedule of Future Minimum Operating Lease Payments (Details) $ in Thousands	Dec. 31, 2015USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,016	$ 776
2,017	313
Total minimum lease payments	$ 1,089

Borrowings - Additional Informa

Borrowings - Additional Information (Detail) - USD ($)

Aug. 05, 2015

Mar. 06, 2013

Jun. 30, 2014

Mar. 31, 2013

Mar. 31, 2014

Dec. 31, 2015

Dec. 31, 2014

Dec. 31, 2013

Jan. 31, 2014

Dec. 31, 2012

Nov. 30, 2012

Apr. 30, 2012

Dec. 31, 2011

Nov. 30, 2011

Debt Instrument [Line Items]

Proceeds from loans payable, net of issuance costs

$ 14,590,000

$ 0

$ 0

Repayments of notes payable

0

6,896,000

4,632,000

Warrants to purchase common stock, exercise price (in USD per share)

$ 1.54

Interest expense on debt

302,000

209,000

472,000

Debt instrument, fair value of success fee

$ 356,000

Payment of final fee

$ 1,200,000

Secured Debt

Debt Instrument [Line Items]

Debt instrument face amount

25,000,000

Proceeds from loans payable, net of issuance costs

15,000,000

Contingent proceeds upon sale of common stock

10,000,000

Proceeds from sale of common stock

$ 25,000,000

Debt stated interest rate

6.99%

Debt term

30 months

Proceeds from sale of stock, convertible subordinated notes, collaboration agreements, grants or development contracts

$ 35,000,000

Enrollment in trial

50.00%

Repayment term

24 months

Covenant, increase in interest rate in event of default

4.00%

Interest expense on debt

$ 699,000

Unused borrowing capacity, fee

$ 250,000

Debt instrument, final fee

8.00%

Debt Instrument, Success Fee

$ 1,000,000

Debt instrument, fair value of success fee

356,000

Payment of final fee

$ 1,200,000

Notes Payable to Banks | Oxford Finance LLC and SVB

Debt Instrument [Line Items]

Debt instrument face amount

$ 8,000,000

$ 4,000,000

Debt effective interest rate

8.22%

8.18%

Debt termination payment percentage

8.25%

Repayments of notes payable

$ 4,454,000

Interest expense on debt

397,000

1,037,000

Notes Payable to Banks | Oxford Finance LLC and SVB | Warrants To Purchase Series C Convertible Preferred Stock

Debt Instrument [Line Items]

Warrants to purchase common stock, exercise price (in USD per share)

$ 11.99

Notes Payable to Banks | Oxford Finance LLC and SVB | Series C Preferred Stock

Debt Instrument [Line Items]

Warrants to purchase shares of stock, shares

20,016

10,008

Warrants to purchase common stock, exercise price (in USD per share)

$ 11.99

Fair value of warrants

$ 163,000

$ 86,000

Convertible Debt | 2010 Wellcome Funding Agreement

Debt Instrument [Line Items]

Interest expense on debt

$ 153,000

Convertible preferred stock issued on conversion

583,162

Percentage of conversion price discount on common stock

20.00%

Convertible preferred stock amount on conversion

$ 5,594,000

Convertible Debt | 2012 Bridge Loan Agreement

Debt Instrument [Line Items]

Debt stated interest rate

6.00%

Interest expense on debt

$ 26,000

Debt maximum amount available

$ 3,000,000

Convertible preferred stock amount on conversion

$ 2,732,000

Convertible Debt | 2012 Bridge Loan Agreement | Series D Preferred Stock

Debt Instrument [Line Items]

Debt conversion price

$ 11.99

Convertible preferred stock issued on conversion

227,784

One-month LIBOR | Secured Debt

Debt Instrument [Line Items]

Debt basis spread on variable rate

1.00%

Three-month LIBOR | Notes Payable to Banks | Oxford Finance LLC and SVB

Debt Instrument [Line Items]

Debt basis spread on variable rate

7.75%

Borrowings - Future Minimum Deb

Borrowings - Future Minimum Debt Payment Obligation (Details) $ in Thousands	Dec. 31, 2015USD ($)
Debt Disclosure [Abstract]
2,016	$ 0
2,017	5,000
2,018	6,000
2,019	4,000
Total principal payments	15,000
Final fee due at maturity in 2019	1,200
Total principal and final fee payments	16,200
Unamortized discount and debt issuance costs	(1,664)
Loan payable, long term	$ 14,536

Stockholders' Equity and Conv51

Stockholders' Equity and Convertible Preferred Stock - Shareholders' Equity (Details) - USD ($)	1 Months Ended		12 Months Ended
	Sep. 30, 2015	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 07, 2015
Class of Stock [Line Items]
Equity instruments, value authorized						$ 150,000,000
Initial public offering, share issued		6,900,000
Proceeds from sales of common stock, net of issuance costs			$ 1,319,000	$ 0	$ 0
Proceeds from issuance of common stock, net of commissions and other costs			1,300,000
Common stock, value remaining available to be sold			$ 28,600,000
Common Stock
Class of Stock [Line Items]
Equity instruments, value authorized						$ 30,000,000
Initial public offering, share issued	197,838		197,838
Share price (in USD per share)	$ 7.05		$ 7.05
Proceeds from sales of common stock, net of issuance costs	$ 1,400,000
Proceeds from issuance of common stock, net of commissions and other costs	$ 1,300,000

Stockholders' Equity and Conv52

Stockholders' Equity and Convertible Preferred Stock - Additional Information (Details) $ / shares in Units, $ in Thousands	Mar. 14, 2014shares	Mar. 31, 2014$ / sharesshares	Nov. 30, 2013USD ($)$ / sharesshares	May. 31, 2013USD ($)tranche$ / sharesshares	Mar. 31, 2013USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Mar. 17, 2014	Jan. 31, 2014$ / sharesshares	Dec. 31, 2012$ / shares
Temporary Equity [Line Items]
Conversion of preferred stock to common stock upon initial public offering | shares	10,386,894	10,386,894
Proceeds from issuance of convertible preferred stock, net of issuance costs | $						$ 0	$ 0	$ 22,200
Class of warrant or right, exercised | shares										909
Warrants to purchase common stock, exercise price (in USD per share) | $ / shares										$ 1.54
Series A Preferred Stock
Temporary Equity [Line Items]
Conversion of stock, conversion ratio									1.15
Series B Preferred Stock
Temporary Equity [Line Items]
Conversion of stock, conversion ratio									1.33
Series C Preferred Stock
Temporary Equity [Line Items]
Conversion of stock, conversion ratio									1
Series D Preferred Stock
Temporary Equity [Line Items]
Conversion of stock, conversion ratio									1
Number of tranches | tranche				2
Convertible preferred stock, shares issued | shares		1,110,252	834,031	148,289
Share price (in USD per share) | $ / shares		$ 11.99	$ 11.99	$ 11.99
Proceeds from issuance of convertible preferred stock, net of issuance costs | $			$ 10,000	$ 1,778	$ 10,581
Convertible preferred stock amount on conversion | $					$ 2,732
Oxford Finance LLC and SVB | Notes Payable to Banks | Series C Preferred Stock
Temporary Equity [Line Items]
Warrants to purchase common stock, exercise price (in USD per share) | $ / shares											$ 11.99

Stockholders' Equity and Conv53

Stockholders' Equity and Convertible Preferred Stock - Summary of Warrants to Purchase Shares of Common Stock (Details) - $ / shares	Dec. 31, 2015	Jan. 31, 2014
Class of Warrant or Right [Line Items]
Shares	30,024
Purchase Price		$ 1.54
April 30, 2012 Warrants | Oxford Finance LLC
Class of Warrant or Right [Line Items]
Shares	11,676
Purchase Price	$ 11.99
April 30, 2012 Warrants | SVB
Class of Warrant or Right [Line Items]
Shares	8,340
Purchase Price	$ 11.99
November 1, 2011 Warrants | Oxford Finance LLC
Class of Warrant or Right [Line Items]
Shares	5,838
Purchase Price	$ 11.99
November 1, 2011 Warrants | SVB
Class of Warrant or Right [Line Items]
Shares	4,170
Purchase Price	$ 11.99

Equity Incentive Plans - 2014 P

Equity Incentive Plans - 2014 Plan (Details) - shares	Jan. 01, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 28, 2014	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares reserved		716,285	1,190,908	163,636
Outstanding shares available for future issuance		893,462	1,111,470	127,277		47,762
2014 Equity Incentive Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares reserved	716,285
Outstanding shares available for future issuance		637,037
Award vesting period		4 years
Award expiration period		10 years
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock under ESPP (in shares)		79,537
Outstanding shares available for future issuance		244,988			145,454
Employee Stock | Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares reserved	179,071

Equity Incentive Plans - Amende

Equity Incentive Plans - Amended and Restated 2003 Stock Plan (Details) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding shares available for future issuance	893,462	1,111,470	127,277	47,762
Number of options outstanding	2,387,337	1,885,372	1,405,550	1,340,433
Stock Incentive Plan 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period	10 years
Award vesting period	4 years
Number of options outstanding	974,196

Equity Incentive Plans - Schedu

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,983	$ 2,050	$ 1,053
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,404	570	351
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,579	$ 1,480	$ 702

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares Available for grant
Beginning balance	1,111,470	127,277	47,762
Additional shares reserved	716,285	1,190,908	163,636
Options granted	(929,100)	(876,163)	(168,231)
Options exercised	0	0	0
Options forfeited	237,007	187,648	75,673
Option expired			8,437
RSUs granted	(291,525)	(168,200)
Ending balance	893,462	1,111,470	127,277
Number of Shares
Beginning balance	1,885,372	1,405,550	1,340,433
Options granted	929,100	876,163	168,231
Options exercised	(190,128)	(208,693)	(19,004)
Options forfeited	(237,007)	(187,648)	(75,673)
Option expired			(8,437)
Ending balance	2,387,337	1,885,372	1,405,550
Vested and exercisable	981,797
Vested and expected to vest	2,238,972
Weighted-Average Exercise Price
Beginning balance	$ 7.95	$ 5.68	$ 5.72
Options granted	7.95	10.15	5.28
Options exercised		3.38	3.65
Options forfeited	10.22	6.29	6.21
Option expired	5.54		5.55
Ending balance	7.92	$ 7.95	$ 5.68
Vested and exercisable	7.64
Vested and expected to vest	$ 7.86
Weighted-Average Remaining Contractual Life (in years)
Outstanding options, weighted-average remaining contractual life (in years)	7 years 7 months 10 days
Options vested and exercisable, weighted-average remaining contractual life (in years)	6 years 3 months 19 days
Options vested and expected to vest, weighted-average remaining contractual life (in years)	7 years 8 months
Aggregate Intrinsic Value (in thousands)
Options exercised, aggregate intrinsic value	$ 923	$ 1,704	$ 65
Outstanding options, aggregate intrinsic value	293
Options vested and exercisable, aggregate intrinsic value	249
Options vested and expected to vest, aggregate intrinsic value	$ 292
Restricted stock units
Shares Available for grant
RSUs granted	(291,525)	(168,200)	(168,200)
RSUs cancelled	49,325
2014 Employment Commencement Incentive Plan
Shares Available for grant
Beginning balance	650,000
Additional shares reserved		650,000
Ending balance	256,425	650,000

Equity Incentive Plans - Summ58

Equity Incentive Plans - Summary of Stock Options Outstanding by Exercise Price Range (Details)	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number of Options (in shares) | shares	2,387,337
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	7 years 7 months 10 days
Vested and Exercisable, Number of Options (in shares) | shares	981,797
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 7.64
$1.65 - $4.73
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	1.65
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 4.73
Options Outstanding, Number of Options (in shares) | shares	240,519
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	5 years 11 months 8 days
Vested and Exercisable, Number of Options (in shares) | shares	204,615
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 4.55
$5.53- $5.86
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	5.53
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 5.86
Options Outstanding, Number of Options (in shares) | shares	324,250
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	9 years 6 months
Vested and Exercisable, Number of Options (in shares) | shares	23,888
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 5.53
$ 6.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	6.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 6.60
Options Outstanding, Number of Options (in shares) | shares	34,620
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	7 years 8 months 28 days
Vested and Exercisable, Number of Options (in shares) | shares	19,952
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 6.60
$ 6.93
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	6.93
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 6.93
Options Outstanding, Number of Options (in shares) | shares	241,162
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	5 years 3 months 28 days
Vested and Exercisable, Number of Options (in shares) | shares	218,890
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 6.93
$6.99- $7.08
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	6.99
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 7.08
Options Outstanding, Number of Options (in shares) | shares	277,650
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	9 years 8 months 10 days
Vested and Exercisable, Number of Options (in shares) | shares	12,277
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 6.99
$ 7.26
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	7.26
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 7.26
Options Outstanding, Number of Options (in shares) | shares	286,535
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	6 years 1 month 29 days
Vested and Exercisable, Number of Options (in shares) | shares	175,681
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 7.26
$8.04- $9.21
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	8.04
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 9.21
Options Outstanding, Number of Options (in shares) | shares	334,800
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	8 years 9 months 10 days
Vested and Exercisable, Number of Options (in shares) | shares	93,521
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 8.45
$9.24- $10.44
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	9.24
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 10.44
Options Outstanding, Number of Options (in shares) | shares	336,252
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	8 years 3 months 8 days
Vested and Exercisable, Number of Options (in shares) | shares	100,395
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 9.77
$11.78-$12.22
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	11.78
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 12.22
Options Outstanding, Number of Options (in shares) | shares	257,189
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	5 years 8 months 24 days
Vested and Exercisable, Number of Options (in shares) | shares	109,768
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 11.99
$ 14.89
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit	14.89
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 14.89
Options Outstanding, Number of Options (in shares) | shares	54,360
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	8 years 5 months 24 days
Vested and Exercisable, Number of Options (in shares) | shares	22,810
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 14.89

Equity Incentive Plans - Stock

Equity Incentive Plans - Stock Options Granted to Employees and Non-Employee Directors (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)	929,100	876,163	168,231
Compensation cost not yet recognized, options	$ 5,922
Compensation cost not yet recognized, period for recognition	3 years
Risk-free interest rate, minimum	1.50%	1.70%	1.20%
Risk-free interest rate, maximum	1.90%	2.00%	1.70%
Volatility, minimum	65.00%	67.00%	68.00%
Volatility, maximum	75.00%	77.00%	69.00%
Expected dividend yield	0.00%	0.00%	0.00%
Options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)	929,100	876,163	168,231
Options granted, weighted average grant date fair value (in dollars per share)	$ 5.02	$ 6.41	$ 3.74
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting upon achievement of stock price target		168,977	23,770
Monte-carlo simulation model
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	2.20%
Risk-free interest rate, maximum	2.80%
Volatility, minimum	60.00%
Volatility, maximum	70.00%
Expected dividend yield	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	5 years 4 months 24 days	5 years 3 months 18 days	5 years 4 months 24 days
Minimum | Monte-carlo simulation model
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	2 years 10 months 25 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 years	6 years 1 month 6 days	6 years 1 month 6 days
Maximum | Monte-carlo simulation model
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 years 3 months 19 days

Equity Incentive Plans - Sche60

Equity Incentive Plans - Schedule of Estimated Grant Date Fair Value of Employee Stock Options Using Black-Scholes Valuation Model (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Volatility, minimum	65.00%	67.00%	68.00%
Volatility, maximum	75.00%	77.00%	69.00%
Risk-free interest rate, minimum	1.50%	1.70%	1.20%
Risk-free interest rate, maximum	1.90%	2.00%	1.70%
Expected dividend yield	0.00%	0.00%	0.00%
Minimum
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Expected term (years)	5 years 4 months 24 days	5 years 3 months 18 days	5 years 4 months 24 days
Maximum
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Expected term (years)	6 years	6 years 1 month 6 days	6 years 1 month 6 days

Equity Incentive Plans - Summ61

Equity Incentive Plans - Summary of Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized, period for recognition	3 years
Number of Shares
RSUs granted	291,525	168,200
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Compensation cost not yet recognized, equity instruments other than options	$ 2,682
Compensation cost not yet recognized, period for recognition	3 years 3 months 15 days
Number of Shares
Beginning balance	168,200	0
RSUs granted	291,525	168,200	168,200
RSUs released	(38,376)
RSUs cancelled	(49,325)
Ending balance	372,024	168,200	0
Weighted-Average Grant Date Fair Value per Share
Beginning balance	$ 9.33	$ 0
RSUs granted	7.76	9.33	$ 9.33
RSUs released	9.42
RSUs cancelled	9.80
Ending balance	$ 8.02	$ 9.33	$ 0
Aggregate Intrinsic Value (in thousands)
Outstanding, Aggregate Intrinsic Value	$ 2,135	$ 2,195

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of the Statutory Tax Rates and the Effective Tax Rates (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory tax rate	34.00%	34.00%	34.00%
State taxes, net of federal benefits	(3.62%)	5.04%	7.10%
Stock-based compensation	(1.20%)	(0.76%)	(0.81%)
Credits	3.30%	3.21%	7.65%
Other	(0.54%)	(1.74%)	(0.01%)
Valuation allowance	(31.94%)	(39.75%)	(47.93%)
Effective tax rate	0.00%	0.00%	0.00%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets, Net [Abstract]
Net operating loss carry forwards	$ 57,558	$ 51,039
Research and development credit	8,531	7,680
Intangible assets	1,994	2,293
Depreciation	195	120
Other	2,396	1,567
Gross Deferred tax assets	70,674	62,699
Less: valuation allowance	(70,674)	(62,699)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Valuation Allowa

Income Taxes - Valuation Allowance and Operating Loss Carryforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance	$ 7,975	$ 7,950	$ 6,295
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	153,649
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	98,459
Research Tax Credit Carryforward | Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	6,915
Research Tax Credit Carryforward | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 4,126

Income Taxes - Tax Credit Carry

Income Taxes - Tax Credit Carryforward and Unrecognized Tax Benefits (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Tax Credit Carryforward [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 820,000	$ 678,000
Unrecognized tax benefits	957,000	0	$ 0	$ 0
Income tax penalties and interest accrued	0	$ 0
Domestic Tax Authority | Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforward	6,915,000
State and Local Jurisdiction | Research Tax Credit Carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforward	$ 4,126,000

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefit Changes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unrecognized Tax Benefit
Balance at beginning of year	$ 0	$ 0	$ 0
Increase related to current year tax provision	162	0	0
Increase related to prior year tax provision	795	0	0
Balance at end of year	$ 957	$ 0	$ 0

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($) $ in Thousands	1 Months Ended			12 Months Ended
	Dec. 31, 2015	Jan. 31, 2011	Dec. 31, 2010	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2003
Compensation and Retirement Disclosure [Abstract]
Maximum annual contributions per employee, percent							100.00%
Employer matching contribution, percent of match			50.00%
Employer matching contribution, percent of employees' gross pay	8.00%	6.00%
Defined contribution plan, cost recognized				$ 255	$ 184	$ 152

Related-Party Transactions (Det

Related-Party Transactions (Details) - 2010 Wellcome Funding Agreement - Convertible Debt - USD ($) $ in Thousands	1 Months Ended
	Mar. 31, 2013	Mar. 31, 2014	Dec. 31, 2012
Related Party Transaction [Line Items]
Convertible preferred stock amount on conversion	$ 5,594
Percentage of conversion price discount on common stock		20.00%
Investor
Related Party Transaction [Line Items]
Unsecured convertible loan			$ 5,594
Convertible preferred stock amount on conversion	$ 5,594
Percentage of conversion price discount on common stock		20.00%

Restructuring Charges - Additio

Restructuring Charges - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended	15 Months Ended
	Dec. 31, 2013	Mar. 31, 2014
Restructuring Cost and Reserve [Line Items]
Cash from asset disposal	$ 2
Accrued facility charges		$ 274
Facilities related and other costs
Restructuring Cost and Reserve [Line Items]
Charges during the period	319
Impairment of Asset
Restructuring Cost and Reserve [Line Items]
Charges during the period	194
Facility Closing | General and administrative expense
Restructuring Cost and Reserve [Line Items]
Charges during the period	$ 125

Selected Unaudited Quarterly 70

Selected Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Contract revenue	$ 4,664	$ 4,476	$ 12,041	$ 4,880	$ 4,259	$ 4,520	$ 5,203	$ 5,988
Operating expenses	15,548	13,006	12,970	11,110	9,140	12,853	8,541	9,222	$ 52,634	$ 39,756	$ 30,476
Interest and other income (expense), net	(382)	(232)	43	51	27	21	(217)	(221)	179	7	183
Net loss	$ (11,266)	$ (8,762)	$ (886)	$ (6,179)	$ (4,854)	$ (8,312)	$ (3,555)	$ (3,455)	$ (27,093)	$ (20,176)	$ (13,112)
Basic and diluted net loss per common share (in dollars per share)	$ (0.61)	$ (0.48)	$ (0.05)	$ (0.34)	$ (0.27)	$ (0.47)	$ (0.20)	$ (1)