Achaogen (AKAOQ) 10-K 27 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	AKAO
Entity Registrant Name	Achaogen Inc
Entity Central Index Key	1,301,501
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		44,725,369
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 753.2

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 145,219	$ 118,964
Short-term investments	19,572	26,912
Contracts receivable	1,357	12,151
Prepaids and other current assets	6,367	2,189
Restricted cash	5,891	127
Total current assets	178,406	160,343
Property and equipment, net	14,810	3,261
Restricted cash	3,855	250
Deposit and other assets		71
Total assets	197,071	163,925
Current liabilities:
Accounts payable	6,862	5,739
Accrued liabilities	15,441	9,698
Loan payable, current portion	12,500	4,167
Deferred revenue	2,100
Other current liabilities		104
Total current liabilities	36,903	19,708
Loan payable, long-term	9,457	21,110
Warrant liability	9,774	13,874
Derivative liability	686	602
Deferred rent	8,289	1,896
Total liabilities	65,109	57,190
Commitments and contingencies (Note 7)
Contingently redeemable common stock (Note 11)	10,000
Stockholders' equity
Common stock, $0.001 par value, 290,000,000 shares authorized at December 31, 2017 and December 31, 2016; 42,515,015 and 35,638,052 shares issued and outstanding at December 31, 2017 and December 31, 2016, respectively	42	35
Preferred stock, $0.001 par value, 10,000,000 shares authorized and zero shares issued and outstanding at December 31, 2017 and December 31, 2016	0	0
Additional paid-in-capital	494,758	353,927
Accumulated deficit	(372,838)	(247,220)
Accumulated other comprehensive loss		(7)
Total stockholders’ equity	121,962	106,735
Total liabilities, contingently redeemable common stock and stockholders’ equity	$ 197,071	$ 163,925

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Common stock, par value (dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	290,000,000	290,000,000
Common stock, shares issued	42,515,015	35,638,052
Common stock, shares outstanding	42,515,015	35,638,052
Preferred stock, par value (dollars per share)	$ 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, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Contract revenue	$ 11,175	$ 41,773	$ 26,061
Operating expenses
Research and development	95,598	73,999	40,228
General and administrative	41,903	17,122	12,406
Total operating expenses	137,501	91,121	52,634
Loss from operations	(126,326)	(49,348)	(26,573)
Interest expense	(2,855)	(2,320)	(699)
Change in warrant and derivative liabilities	1,928	(19,859)	(19)
Other income, net	1,635	300	198
Net loss	$ (125,618)	$ (71,227)	$ (27,093)
Basic and diluted net loss per common share	$ (3.17)	$ (3)	$ (1.49)
Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share	39,645,635	23,707,063	18,147,986

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (125,618)	$ (71,227)	$ (27,093)
Other comprehensive (loss) income:
Net unrealized gain (loss) on available-for-sale securities	7	41	(16)
Total comprehensive loss	$ (125,611)	$ (71,186)	$ (27,109)

Consolidated Statements of Cont

Consolidated Statements of Contingently Redeemable Common Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Private Placement	Underwriter	Contingently Redeemable Common Stock	Contingently Redeemable Common StockPrivate Placement	Common Stock	Common StockPrivate Placement	Common StockUnderwriter	Additional Paid-In Capital	Additional Paid-In CapitalPrivate Placement	Additional Paid-In CapitalUnderwriter	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2014	$ 64,613					$ 18			$ 213,527			$ (148,900)	$ (32)
Beginning balance (in shares) at Dec. 31, 2014						17,907,135
Increase (Decrease) in Stockholders' Equity:
Issuance of common stock upon initial public offering, net of issuance costs	1,319								1,319
Issuance of common stock upon initial public offering, net of issuance costs (in shares)						197,838
Issuance of common stock under stock plans	1,053								1,053
Issuance of common stock under stock plans (in shares)						228,504
Issuance of common stock under ESPP	300								300
Issuance of common stock under ESPP (in shares)						61,742
Stock-based compensation expense	2,983								2,983
Unrealized gain (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
Increase (Decrease) in Stockholders' Equity:
Issuance of common stock upon initial public offering, net of issuance costs	3,827	$ 22,587	$ 94,547			$ 1	$ 8	$ 7	3,826	$ 22,579	$ 94,540
Issuance of common stock upon initial public offering, net of issuance costs (in shares)						907,711	7,999,996	7,475,000
Issuance of common stock under stock plans	65								65
Issuance of common stock under stock plans (in shares)						103,912
Issuance of common stock under ESPP	401								401
Issuance of common stock under ESPP (in shares)						145,724
Issuance of common stock upon exercise of warrant	9,488					$ 1			9,487
Issuance of common stock upon exercise of warrant (in shares)						610,490
Stock-based compensation expense	3,847								3,847
Unrealized gain (loss) on available-for-sale securities, net of taxes	41												41
Net loss	(71,227)											(71,227)
Ending balance at Dec. 31, 2016	$ 106,735					$ 35			353,927			(247,220)	(7)
Ending balance (in shares) at Dec. 31, 2016	35,638,052					35,638,052
Increase (Decrease) in Stockholders' Equity:
Issuance of contingently redeemable common stock					$ 10,000
Issuance of contingently redeemable common stock (in shares)					407,331
Issuance of common stock upon initial public offering, net of issuance costs			$ 121,192					$ 6			$ 121,186
Issuance of common stock upon initial public offering, net of issuance costs (in shares)								5,750,000
Issuance of common stock under stock plans	$ 1,645					$ 1			1,644
Issuance of common stock under stock plans (in shares)						413,333
Issuance of common stock under ESPP	1,323								1,323
Issuance of common stock under ESPP (in shares)						186,455
Issuance of common stock upon exercise of warrant	2,506								2,506
Issuance of common stock upon exercise of warrant (in shares)						119,844
Stock-based compensation expense	14,172								14,172
Unrealized gain (loss) on available-for-sale securities, net of taxes	7												$ 7
Net loss	(125,618)											(125,618)
Convertible preferred stock, ending balance at Dec. 31, 2017				$ 10,000
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2017				407,331
Ending balance at Dec. 31, 2017	$ 121,962					$ 42			$ 494,758			$ (372,838)
Ending balance (in shares) at Dec. 31, 2017	42,515,015					42,107,684

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (125,618)	$ (71,227)	$ (27,093)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,334	441	426
Amortization of (discount) premium on short-term investments	(227)	304	500
Stock-based compensation expense	14,172	3,847	2,983
Loss on fixed asset disposition	54
Change in warrant and derivative liabilities	(1,928)	19,859	19
Non-cash interest expense relating to notes payable	847	741	302
Change in operating assets and liabilities:
Contracts receivable	10,794	(7,112)	195
Prepaids and other assets	(4,107)	(199)	(1,504)
Accounts payable and accrued liabilities	5,736	6,668	3,076
Deferred revenue	2,100
Other liabilities	1,588	(225)	8
Net cash used in operating activities	(95,255)	(46,903)	(21,088)
Cash flows from investing activities:
Purchase of property and equipment	(7,106)	(901)	(606)
Purchase of short-term investments	(121,796)	(30,961)	(41,851)
Maturities of short-term investments	129,370	42,230	47,689
Net cash provided by investing activities	468	10,368	5,232
Cash flows from financing activities:
Proceeds from underwritten public offering, net of issuance costs	121,192	94,852
Proceeds from issuance of contingently redeemable common stock	10,000
Proceeds from private placement, net of issuance costs		25,166
Proceeds from sales of common stock, net of issuance costs		3,827	1,319
Proceeds from the issuance of common stock in connection with equity incentive plans	2,968	466	1,353
Proceeds from exercise of stock warrants	418	1,151
Proceeds from loan payable, net of issuance costs		10,000	14,590
Repayment of loan payable	(4,167)
Net cash provided by financing activities	130,411	135,462	17,262
Net increase in cash, cash equivalents, and restricted cash	35,624	98,927	1,406
Cash, cash equivalents, and restricted cash at beginning of year	119,341	20,414	19,008
Cash, cash equivalents, and restricted cash at end of year	154,965	119,341	20,414
Supplemental disclosures of cash flow information
Interest paid	2,008	1,579	396
Supplemental disclosures of noncash investing and financing information
Reclassification of warrant liability to additional paid-in capital	2,088	8,337
Accrued and deferred public offering issuance cost		305
Issuance of derivative in connection with issuance of loan payable			$ 356
Purchases of property and equipment included in accounts payable and accrued liabilities	1,130
Purchases of property and equipment included in deferred rent	$ 4,701	$ 1,896

Organization and Basis of Prese

Organization and Basis of Presentation and Consolidation	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation and Consolidation	1. Organization and Basis of Presentation and Consolidation Achaogen, Inc. (together with its consolidated subsidiary, the “Company”) is a late-stage biopharmaceutical company passionately committed to the discovery, development, and commercialization of innovative antibacterial treatments against multi-drug resistant (“MDR”) gram-negative infections. The Company is developing plazomicin, its lead product candidate, for the treatment of bacterial infections due to MDR Enterobacteriaceae, including carbapenem-resistant Enterobacteriaceae (“CRE”). On October 26, 2017, the Company announced the submission of a New Drug Application (“NDA”) to the U.S. Food and Drug Administration (“FDA”) for plazomicin, seeking approval to treat complicated urinary tract infections (“cUTI”), including acute pyelonephritis (“AP”) and bloodstream infections (“BSI”) due to certain Enterobacteriaceae in patients who have limited or no alternative treatment options. The NDA is supported by data from two Phase 3 clinical trials, EPIC (Evaluating Plazomicin In cUTI) and CARE (Combating Antibiotic Resistant Enterobacteriaceae), which evaluated the safety and efficacy of plazomicin in patients with serious infections caused by gram-negative pathogens, including ESBL producing Enterobacteriaceae and CRE. The EPIC study was a Phase 3 trial of plazomicin for the treatment of patients with cUTI and acute pyelonephritis (“AP”). The CARE study was a Phase 3 resistant pathogen trial designed to evaluate the efficacy and safety of plazomicin in patients with serious bacterial infections due to CRE. The Company is also developing an orally available antibacterial candidate, C-Scape, a combination of ceftibuten, an approved third generation cephalosporin, and clavulanate, an approved b - l a c t a m a s e i n h i b i t o r t o a d d r e s s a s e r i o u s u n m e t n e e d f o r e f f e c t i v e o r a l t r e a t m e n t f o r p a t i e n t s w i t h c U T I , i n c l u d i n g A P , c a u s e d b y E S B L - p r o d u c i n g E n t e r o b a c t e r i a c e a e . O n J a n u a r y 2 , 2 0 1 8 , t h e C o m p a n y a n n o u n c e d p o s i t i v e P h a s e 1 t o p - l i n e r e s u l t s a n d t h e C o m p a n y i n t e n d s t o i n i t i a t e a s i n g l e p i v o t a l P h a s e 3 s t u d y i n p a t i e n t s w i t h c U T I , i n c l u d i n g A P , w h o a r e s u i t a b l e f o r t r e a t m e n t w i t h o r a l a n t i b i o t i c s , i n 2 0 1 8 . The Company was incorporated in Delaware in 2002 and commenced operations in 2004. Since commencing operations in 2004, the Company has devoted substantially all 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. Reclassifications The change in derivative liability on the consolidated statements of operations for the year ended December 31, 2015 has been reclassified to be included in the change in warrant and derivative liabilities to conform to the current year’s presentation. Such reclassifications did not impact the Company’s net loss or financial position. The cash and cash equivalents on the condensed consolidated statements of cash flows for the year ended December 31, 2015 has been reclassified to include restricted cash to conform to the current period’s presentation. Such reclassification did not impact the Company’s net loss or financial position. 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, 2017, 2016 and 2015. Liquidity and Going Concern 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 the Company’s 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, 2017, the Company had sold 1,105,549 shares pursuant to its ATM equity offering program at a weighted-average price of $4.82 per share for aggregate offering proceeds of $5.3 million and aggregate net proceeds of $5.1 million, after deducting the sales commissions and offering expenses. On June 3, 2016, the Company sold 7,999,996 shares of its common stock and warrants to purchase 1,999,999 shares of its common stock pursuant to Securities Purchase Agreement (the "Purchase Agreement") for aggregate gross proceeds of $25.4 million and aggregate net proceeds of $25.1 million, after deducting the issuance costs, in connection with a private placement financing transaction (the "Private Placement"). The warrants have an exercise price of $3.66 per share and are exercisable up to five years from the date of issuance. On December 19, 2016, the Company completed an underwritten public offering of common stock made under a prospectus supplement and related prospectus pursuant to the Shelf Registration Statement. This offering resulted in the sale of 7,475,000 shares, at a price of $13.50 per share, including the full exercise of the underwriter’s option to purchase an additional 975,000 shares of common stock. The Company received net proceeds from the offering of $94.6 million, after deducting the underwriting discounts and commissions and estimated offering expenses. On May 4, 2017, the Company entered into an agreement with the Bill & Melinda Gates Foundation (the “Gates Foundation”) to discover drug candidates against gram-negative bacterial pathogens intended to prevent neonatal sepsis (the “Grant Agreement”). Pursuant to the Grant Agreement, the Gates Foundation awarded the Company up to approximately $10.5 million in grant funding (“Grant Funds”) over a three-year research term, of which approximately $3.2 million was received in May 2017 (the “Advance Funds”). Concurrently with the Grant Agreement, the Company entered into a Common Stock Purchase Agreement (the “Gates Purchase Agreement”) with the Gates Foundation, pursuant to which the Company agreed to sell 407,331 shares of its contingently redeemable common stock to the Gates Foundation in a private placement at a purchase price per share equal to $24.55, for gross proceeds to the Company of $10.0 million (“Gates Investment”). In connection with the Grant Agreement and the Gates Investment, the Company entered into a strategic relationship with the Gates Foundation (the “Letter Agreement”). Under the terms of the Letter Agreement, the Gates Investment and Grant Funds may only be used to conduct mutually agreed upon work, including the scale up of the Company’s antibody platform technology to launch a product intended to prevent neonatal sepsis (the “NSP”). Pursuant to the Letter Agreement, the Company agreed to make the NSP available and accessible in certain developing countries and to grant the Gates Foundation a non-exclusive license to commercialize selected drug candidates in certain developing countries, which may only be exercised in the event of certain defaults as described in the Letter Agreement (the “Global Access Commitments”). The Global Access Commitments will continue in effect until the earlier of 25 years from the closing of the Gates Investment or 7 years following the termination of all funding provided by the Gates Foundation; provided, that the Global Access Commitments will continue for any products or services developed with funding provided by the Gates Foundation which continue to be developed or available in certain developing countries. On May 31, 2017, the Company completed an underwritten public offering of 5,750,000 shares of its common stock at a price to the public of $22.50 per share, including the closing of the full exercise of the underwriters’ option to purchase an additional 750,000 shares of common stock on June 9, 2017. The Company received net proceeds from the offering of $121.2 million, after deducting the underwriting discounts and commissions and offering expenses. In September 2017, the Company was awarded a contract (“C-Scape Contract”) valued at up to $18.0 million in grant funding from the Biomedical Advanced Research and Development Authority (“BARDA”) to support the development of C-Scape. The C-Scape Contract includes a base period with committed funding of $12.0 million and subsequent option periods that, if exercised, would bring the total value of the award to $18.0 million. The Company has incurred losses and negative cash flows from operations every year since its inception. As of December 31, 2017, the Company had unrestricted cash, cash equivalents and short-term investments of approximately $164.8 million and an accumulated deficit of approximately $372.8 million. Management expects that, based on its current operating plans, the Company’s existing cash, cash equivalents and short-term investments will be sufficient to fund its current planned operations for at least the next twelve months from the issuance of this report. Management plans to raise additional funds through equity or debt financing arrangements, government contracts, and/or third-party collaboration funding in the future to fund its operations, including the commercial launch of plazomicin. 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 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, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. 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 and warrant 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, 2017 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 amount of the loan payable approximates its fair value. The warrant and derivative liabilities are recorded at estimated fair value with changes in estimated fair value recorded in the Company’s statements of operations. 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, 2017 and 2016, cash and cash equivalents consisted of bank deposits, cash, commercial paper, money market funds, cash repurchase agreement investments and overnight cash sweep investments in government 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 As of December 31, 2017 and 2016, the Company had restricted cash of $9.7 million and $0.4 million, respectively. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheet that sum to the total of the same such amounts shown in the consolidated statements of cash flows (in thousands): Year Ended December 31, 2017 2016 2015 Cash and cash equivalents $ 145,219 $ 118,964 $ 20,287 Restricted cash, current 5,891 127 - Restricted cash, non-current 3,855 250 127 Total cash, cash equivalents, and restricted cash $ 154,965 $ 119,341 $ 20,414 In May 2017, the Company received $13.2 million of funding from the Gates Foundation from the Grant Funds and Gates Investment (see Note 1). The Letter Agreement restricts the Company’s use to expenditures that are reasonably attributable to the activities required to support the research projects funded by the Gates Foundation, including an allocation of overhead and administrative expenses. As of December 31, 2017 and 2016 the Company had $9.2 million and zero, respectively, of restricted cash related to the unspent cash provided by the Gates Foundation. The remaining restricted cash serves as collateral for the letters of credit provided as security deposits under the Company’s facility lease and expire approximately 90 days from the end of their respective lease terms. As of December 31, 2017 and 2016, the Company had $0.5 million and $0.4 million, respectively, of restricted cash, which relates to the Company’s facility leases. 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 regarding resource allocation and assessing performance. The Company has one operating segment. Customer Concentration For the years ended December 31, 2017, 2016 and 2015, all of the Company’s revenue has been generated from funding pursuant to U.S. government contracts and a non-profit foundation grant. 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 with balances that generally 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. The Company’s 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, 2017 and 2016, 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, 2017 and 2016, as the Company expects full collection of the receivable balances. Property and Equipment, Net Property and equipment consist of office equipment, laboratory equipment, and leasehold improvements and are 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 seven 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 years ended December 31, 2017, 2016 and 2015, the Company did not have any impairment charges. Warrant Liability On June 3, 2016, the Company issued warrants to purchase 1,999,999 shares of its common stock in connection with the Private Placement. Each warrant has an exercise price of $3.66 per share and is exercisable for five years from the date of issuance. The Company accounts for these warrants as a liability instrument measured at estimated fair value. The initial fair value of the warrants was determined using a calibration model that involved the Black-Scholes Pricing Model ("Black-Scholes"), which requires inputs such as the risk-free interest rate, expected share price volatility, underlying price per share of the Company's common stock and remaining term of the warrants. The warrants are subject to remeasurement at each balance sheet date, using Black-Scholes, with any changes in the fair value of the outstanding warrants recognized in the condensed consolidated statements of operations. As of December 31, 2017, warrants to purchase 1,178,782 shares of the Company’s common stock remain outstanding and unexercised. Contingently Redeemable Common Stock In May 2017, the Company agreed to sell 407,331 shares of its contingently redeemable common stock to the Gates Foundation in a private placement at a purchase price per share equal to $24.55 (see Note 1). Common stock with embedded redemption features that are settled at the option of the holder, are considered redeemable common stock. Redeemable common stock is considered to be temporary equity and presented in a section between liabilities and equity on the Company’s consolidated balance sheets. Subsequent adjustment of the amount presented in temporary equity is required only if the Company determines that it is probable that the instrument will become redeemable. Upon termination of the redemption features, the redeemable common stock is reclassified into equity. As of December 31, 2017, 407,331 shares of contingently redeemable common stock remain as temporary. 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 2017 and 2016, 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 from government contracts and a non-profit foundation grant. Government contracts 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 or grant arrangements are recorded as revenue if the Company is deemed to be the principal participant in the arrangements because the activities under the contracts or grants are part of the Company’s development programs. If the Company is not the principal participant, the funds from contracts or grants are recorded as a reduction to research and development expense. Contract funds received are not refundable and are recognized when the related qualified research and development costs are incurred and there is reasonable assurance that the funds will be received. Funds received in advance are recorded as deferred revenue. Management has determined that the Company is the principal participant under the Company’s government contract arrangements and non-profit grant agreement, and accordingly, the Company records amounts earned under these arrangements as 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, non-profit grants 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 recognized as an expense as the goods are delivered or the related services are performed. For certain research and development services where the Company has not yet been invoiced or otherwise notified of actual cost from the third-party contracted service providers, the Company is required to estimate the extent of the services that have been performed on the Company’s behalf and the associated costs incurred at each reporting period. The majority of the service providers invoice the Company monthly in arrears for services performed. The Company make estimates of the accrued expenses as of each balance sheet date in the consolidated financial statements based on facts and circumstances known to the Company at that time. The Company periodically confirms the accuracy of the estimates with the service providers and makes adjustments if necessary. Examples of estimated accrued research and development expenses include services from: • contract research organizations (“CROs”) and other service providers in connection with clinical studies; • contract manufacturers in connection with the production of clinical trial materials; and • vendors in connection with preclinical development activities. The Company bases the expenses related to preclinical studies and clinical trials on estimates of the services received and efforts expended pursuant to contracts with multiple research institutions and CROs that conduct and manage such studies and trials on the Company’s behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract, and may result in uneven payment flows and expense recognition. Payments under some of these contracts depend on factors such as the successful enrollment of patients and the completion of clinical trial milestones. In accruing service fees, the Company estimates the time period over which these services will be performed and the level of effort to be expended and costs to be incurred during each reporting period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company adjusts the accrual accordingly. The Company’s estimation of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in reporting changes in estimates in any particular period. To date, there have been no material adjustments from the Company’s estimates to the amount actually incurred. 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. The Company assesses the need for a valuation allowance against the Company’s deferred income tax assets by considering both positive and negative evidence related to whether it is more likely than not that the deferred income tax assets will be realized. In evaluating its ability to recover the deferred income tax assets within the jurisdiction from which they arise, the Company considered all available positive and negative evidence, including scheduled reversals of deferred income tax liabilities, projected future taxable income, tax-planning strategies, and results of recent operations. Due to the Company’s considerations, 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. The Company has reported a net loss for the years ended December 31, 2017, 2016 and 2015, and diluted net loss per common share is the same as basic net loss per common share for those periods. The following table sets forth the computation of the basic and diluted net loss per share during the years ended December 31, 2017, 2016 and 2015 (in thousands, except share and per share amounts): Year Ended December 31, 2017 2016 2015 Net loss $ (125,618 ) $ (71,227 ) $ (27,093 ) Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share 39,645,635 23,707,063 18,147,986 Basic and diluted net loss per common share $ (3.17 ) $ (3.00 ) $ (1.49 ) The following potentially dilutive securities outstanding have been excluded from diluted net loss per share, because their effect would be antidilutive, as of December 31, 2017, 2016 and 2015: December 31, 2017 2016 2015 Options to purchase common stock 4,838,598 3,540,293 2,387,337 Restricted stock units 891,232 605,052 372,024 Warrants to purchase common stock 1,196,296 1,322,754 30,024 Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which provides a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and will supersede most current revenue recognition guidance. 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 Company expects to be entitled in exchange for those goods or services. This ASU defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing GAAP. The Company expects to adopt the new revenue standard as of January 1, 2018 using the modified retrospective method. The Company has completed its assessment and determined that its government contracts and non-profit foundation grant are not in scope of ASC 606 and there is no impact on its consolidated financial statements. In March 2016, the FASB issued ASU No 2016-09, Compensation - Stock Compensation Improvements to Employee Share-Based Payment Accounting In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, restricted cash, 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. Where quoted prices are available in an active market, securities are classified as Level 1 in the valuation hierarchy, including cash held at overnight sweep accounts. The Company’s Level 2 valuations of marketable securities are generally derived from independent pricing services based upon quoted prices in active markets for similar securities, with prices adjusted for yield and number of days to maturity, or based on industry models using data inputs, such as interest rates and prices that can be directly observed or corroborated in active markets. In certain cases, where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. Level 3 liabilities that are measured at estimated fair value on a recurring basis consist of a derivative liability in connection with loan payable and a warrant liability in connection with the Private Placement. 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, 2017 and 2016. 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, 2017: December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Assets Level 1: Restricted cash 9,746 — — 9,746 Money market funds 58,769 — — 58,769 U.S. Treasury bills 4,992 — — 4,992 Subtotal 73,507 — — 73,507 Level 2: Commercial paper 46,040 — — 46,040 U.S. agency securities 4,990 — — 4,990 Other debt securities 50,000 — — 50,000 Subtotal 101,030 — — 101,030 Total $ 174,537 $ — $ — $ 174,537 Reported as: Cash and cash equivalents $ 145,219 Short-term investments $ 19,572 Restricted cash $ 9,746 Liabilities, Level 3 Warrant Liability $ 9,774 Derivative Liability $ 686 Total $ 10,460 As of December 31, 2016: December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Assets Cash $ 3,728 $ — $ — $ 3,728 Level 1: Restricted cash 377 — — 377 Money market funds 115,236 — — 115,236 Subtotal 115,613 — — 115,613 Level 2: Corporate debt securities 12,969 — (7 ) 12,962 Commercial paper 13,950 — — 13,950 Subtotal 26,919 — (7 ) 26,912 Total $ 146,260 $ — $ (7 ) $ 146,253 Reported as: Cash and cash equivalents $ 118,964 Short-term investments $ 26,912 Restricted cash $ 377 Liabilities, Level 3 Warrant liability $ 13,874 Derivative liability $ 602 Total $ 14,476 All available-for-sale securities held as of December 31, 2017 had contractual maturities of less than one year from the date of acquisition. There were no sales of available-for-sale securities in any of the periods presented. There were no securities that were in unrealized loss positions as of December 31, 2017. 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 approval to market plazomicin from the FDA. 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 estimated fair value of the Success Fee is recorded as a derivative liability and included in other long-term liabilities on the accompanying consolidated balance sheet. As of December 31, 2017 the derivative liability increased by $84,000 to $686,000 from December 31, 2016, primarily as a result of the time value of money, which is presented as a component of change in warrant and derivative liabilities in the Company’s condensed consolidated statements of operations for the year ended December 31, 2017. 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 a change in the discount rate. If the discount rate decreased by 5%, the fair value of the derivative liability as of December 31, 2017 would change by approximately $59,000. For the year ended December 31, 2017, there was no change to the key assumptions used in the calculation of the estimated fair value. Any changes in the estimated fair values are presented as changes in warrant and derivative liabilities in the Company's consolidated statements of operations. Pursuant to the Private Placement (see Note 2), the Company issued warrants to purchase 1,999,999 shares of common stock at an exercise price of $3.66 per share. The Company classified these warrants as a liability measured at fair value using Black-Scholes. Under certain entity conditions, the holder of a warrant may require the Company to settle the warrant in cash at its estimated fair value using Black-Scholes. On the closing date of the Private Placement, June 3, 2016, the $2.6 million initial estimated fair value of the warrants was recorded as a warrant liability on the accompanying consolidated balance sheet. At December 31, 2017 and 2016, the estimated fair value of the warrants was approximately $9.8 million and $13.9 million, respectively. The change in the estimated fair value is primarily due to the decrease in the Company's stock price and is included in changes in warrant and derivative liabilities in the Company's consolidated statements of operations. During the year ended December 31, 2016, certain holders of these warrants exercised 707,269 warrants. The Company received $1.2 million in proceeds from these warrant exercises. The Company is required to record the exercised warrants at its estimated fair value at the time of exercise, with any change included in changes in warrant and derivative liabilities in the Company’s consolidated statements of operations. The Company estimated the fair value of these exercised warrants at their respective exercise dates to be $8.3 million, an increase of $7.4 million from its initial valuation, at June 3, 2016, of $0.9 million, primarily due to an increase in the Company’s stock price. During the year ended December 31, 2017, certain holders of these warrants exercised warrants to purchase 113,948 shares of common stock. The Company received $0.4 million in proceeds from these warrant exercises. The Company is required to record the exercised warrants at its estimated fair value at the time of exercise, with any change included in changes in warrant and derivative liabilities in the Company’s consolidated statements of operations. The Company estimated the fair value of these exercised warrants at their respective exercise dates to be $2.1 million, an increase of $0.9 million from its valuation, at December 31, 2016, of $1.2 million, primarily due to an increase in the Company’s stock price. The fair value of the warrant liability is classified as a Level 3 measurement within the fair value hierarchy since the Company’s valuation utilized significant unobservable inputs, including the risk-free interest rate, expected share price volatility, underlying price per share of the Company's common stock and remaining term of the warrants. The estimated fair values of the warrants were determined using Black-Scholes with the following assumptions, during the years ended December 31, 2017 and 2016: December 31, 2017 December 31, 2016 Expected volatility 80% 60 - 80% Expected term 3.4 - 4.3 years 4.4 - 5.0 years Risk-free interest rate 1.6 - 2.0% 1.0 - 1.9% Dividend yield —% —% The expected volatility is based on the Company's expected volatility. The expected term is based on the remaining life of the warrants. The risk-free interest rate is obtained from the yields on actively traded U.S. Treasury securities for a period equal to the expected term of the warrants. The dividend yield is zero because the Company has never paid cash dividends and has no present intention to pay cash dividends. Should the share price change by 5%, the fair value of the warrant liability as of December 31, 2017 would change by approximately $593,000. 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 December 31, 2017, 2016 and 2015 (in thousands): Estimated Fair Value of Derivative Liability Estimated Fair Value of Warrant Liability Balance of Level 3 Liabilities at December 31, 2014 $ — $ — Estimated fair value of derivative liability issued 356 — Change in estimated fair value of derivative liability 19 — Balance of Level 3 Liabilities at December 31, 2015 375 — Estimated fair value of warrants issued — 2,579 Change in estimated fair value of warrant liability — 19,632 Reclassification of warrant liability to additional paid-in-capital upon exercise of warrants — (8,337 ) Change in estimated fair value of derivative liability 227 — Balance of Level 3 Liabilities at December 31, 2016 602 13,874 Change in estimated fair value of warrant liability — (2,012 ) Reclassification of warrant liability to additional paid-in-capital upon exercise of warrants — (2,088 ) Change in estimated fair value of derivative liability 84 — Balance of Level 3 Liabilities at December 31, 2017 $ 686 $ 9,774 Warrants outstanding as of December 31, 2017 have a weighted-average exercise price of $3.78.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Balance Sheet Components	4. Balance Sheet Components Prepaids and other current assets Prepaids and other current assets consisted of the following (in thousands): December 31, 2017 December 31, 2016 Deferred research and development costs $ 4,317 $ 660 Prepaid expenses 1,755 1,390 Other current assets 295 139 $ 6,367 $ 2,189 Property and Equipment, net Property and equipment, net consisted of the following (in thousands): December 31, 2017 2016 Office equipment $ 863 $ 644 Laboratory equipment 6,663 4,038 Leasehold improvements 9,355 1,072 Construction-in-progress 1,040 1,896 Property and equipment, gross 17,921 7,650 Less: accumulated depreciation (3,111 ) (4,389 ) Property and equipment, net $ 14,810 $ 3,261 Depreciation expense for the years ended December 31, 2017, 2016 and 2015 was $1.3 million, $0.4 million and $0.4 million, respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): December 31, 2017 2016 Accrued clinical and development expenses $ 6,480 $ 3,681 Payroll and related bonus expenses 6,281 4,941 Other 2,680 1,076 $ 15,441 $ 9,698

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Agreements	5. License and Collaboration Agreements Thermo Fisher Scientific, Inc. In April 2016, the Company entered into an agreement with its collaboration partner, Thermo Fisher Scientific, Inc. (“Thermo Fisher”), to develop and commercialize an assay to support plazomicin. If approved, the Company and Thermo Fisher plan to have a commercial assay for plazomicin available at launch to enable patients to receive safe and efficacious doses of plazomicin. In accordance with the terms of the agreement, the Company is required to make milestone payments with respect to research, development, regulatory and commercialization milestones (if any). All such milestone payments may total, in aggregate, up to but no more than $6.8 million, per the November 2017 amended agreement. In further consideration of this agreement, in the event of a successful commercialization of the assay, the Company is required to pay a minimum threshold annual revenue to Thermo Fisher. For the years ended December 31, 2017, December 31, 2016 and December 31, 2015 the milestone payments and the cost recorded as research and development expense were $2.5 million$1.2 million and zero, respectively. Crystal Biosciences, Inc. In May 2016, the Company entered into a collaboration and license agreement with Crystal Biosciences, Inc. (“Crystal”). Pursuant to the terms of this agreement, the Company and Crystal agreed to collaborate on the discovery of monoclonal antibodies against multiple targets. Crystal agreed to conduct the initial discovery work with its antibody platform and the Company has the right to develop and commercialize the antibodies discovered through this collaboration. The Company is required to provide signing and milestone payments with respect to research, development, regulatory and commercialization milestones (if any). All such milestone payments may total, in aggregate, up to but no more than $20.6 million. The upfront signing fee, technology access fees and research funding were recorded as research and development expense during the years ended December 31, 2017 and 2016. This collaboration and license agreement also provides that the Company shall pay royalties equal to a low single-digit percentage of annual worldwide net sales of the commercialized product. 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 $1.5 million 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 $19.5 million for the first product and $9.8 million following the second product commercialized under the agreement with Ionis. The Company is also required to pay additional milestone payments of up to $20.0 million 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 any licensed products, including, if applicable, plazomicin. Through December 31, 2017, the Company had compensated Ionis $7.0 million in connection with the first three milestones under the license for the first aminoglycoside product candidate. For the years ended December 31, 2017, December 31, 2016 and December 31, 2015 the milestone payments and the cost recorded as research and development expense were zero.

Revenue Contracts

Revenue Contracts	12 Months Ended
	Dec. 31, 2017
Contractors [Abstract]
Revenue Contracts	6. Revenue Contracts Certain of the Company’s drug discovery and development activities are performed under contracts with the Gates Foundation and 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. Bill & Melinda Gates Foundation In May 2017, the Company entered into an agreement with the Gates Foundation to discover drug candidates against gram-negative bacterial pathogens intended to prevent neonatal sepsis (the “Grant Agreement”). The Gates Foundation awarded the Company up to approximately $10.5 million in grant funding (“Grant Funds”) over a three-year research term. Approximately $3.2 million of funding was received in May 2017 (the “Advance Funds”) of which $2.1 million was recorded as deferred revenue as of December 31, 2017. The Advance Funds are replenished by the Gates Foundation each calendar year, or sooner, following the Company’s submission of a progress report, including expenses incurred for the research activities. Under certain conditions, as described in the Grant Agreement, the Gates Foundation may terminate the Grant Agreement and the Company is obligated to return to the Gates Foundation any unused portion of the Advance Funds. The Company recorded contract revenue of $1.1 million under this agreement for the year ended December 31, 2017. The Company did not record any contract revenue from the Gates Foundation during 2016. BARDA In August 2010, the Company was awarded a contract with 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 $27.6 million for the first two years of the contract and subsequent options exercisable by BARDA to provide additional funding. In September 2012, BARDA exercised an additional $15.8 million contract option ("Option 1"), which increased the total contract committed funding to $43.4 million through March 2014. In April 2013, the Company was awarded an additional $60.4 million under the contract to support its Phase 3 clinical trial of plazomicin ("Option 2") to increase the total committed funding under this contract to $103.8 million. In May 2016, the Company was awarded an additional $20.0 million ("Option 3") under the contract to support its Phase 3 EPIC trial of plazomicin. In April 2017, BARDA modified Option 1 to allow for an additional $0.5 million of contract funding. This brings the total committed funding under this contract to $124.3 million, of which a total of $124.3 million has been recorded as revenue through December 31, 2017. During the years ended December 31, 2017, 2016, and 2015, the Company recognized revenue of $7.7 million, $39.5 million and $17.6 million, respectively, under this agreement, of which zero and $11.7 million were included in contracts receivable at December 31, 2017 and 2016, respectively. In September 2017, the Company was awarded the C-Scape Contract (“C-Scape Contract”) from BARDA to support the development of C-Scape. The C-Scape Contract includes a base period with committed funding of $12.0 million and subsequent option periods that, if exercised, would bring the total value of the award to $18.0 million. For the year ended December 31, 2017, the Company recorded revenue of $1.0 million with $11.0 million remaining available. As of December 31, 2017, $1.0 million was included in contracts receivable. DTRA In November 2012, 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. As of December 31, 2017, the contract and final settlement are complete. NIAID In July 2015, the Company was awarded a contract by the National Institute of Allergy and Infectious Diseases ("NIAID") to support the discovery and development of LpxC inhibitors for the treatment of bacterial infections for $1.5 million committed through June 30, 2016. In January 2016, an additional committed funding of $0.5 million was added. In April 2016, NIAID modified the contract to exercise the first option to increase the total contract committed funding to $4.4 million. In April 2017, NIAID modified the contract to add committed funding of $0.3 million to the first option, bringing the total committed funding to $4.7 million. In June 2017, NIAID modified the contract to exercise the second option of $0.6 million and extended performance through August 2018, bringing the total committed funding to $5.3 million, of which $0.4 million remains available as of December 31, 2017. During 2017, the Company decided to discontinue all research and development efforts on its preclinical LpxC inhibitor programs for gram-negative pathogens. The Company does not expect to recognize additional revenues under this contract in future periods. During the years ended December 31, 2017, 2016 and 2015, the Company recognized revenue of $1.3 million, $2.3 million and $1.4 million, respectively, under these agreements, of which $0.2 million and $0.5 million were included in contracts receivable at December 31, 2017 and 2016, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments	7. Commitments Facility Lease Agreement In August 2016, the Company entered into a non-cancelable agreement (the "Lease") to lease 47,118 square feet of office, laboratory and research and development space (the “Original Space”) for the Company's new principal executive offices in South San Francisco. In July 2017, the Company entered into an amendment (the “Lease Amendment”) to lease an additional 51,866 square feet of space (the “Expansion Space”) for a total of 98,984 square feet (the “Premises”). The Lease commenced in March 2017, after the substantial completion of certain improvements (“Tenant Improvements”) required under the Lease and the Company moved into the Original Space in April 2017. The lease for 18,888 square feet of the Expansion Space commenced in August 2017 and the remainder is expected to begin by the end of the second quarter 2018. The lease term for the Premises is through January 31, 2028 (the “Lease Term”) and contains an option to extend the Lease Term for an additional 5 years. Base rent for the first year for the Original Space and Expansion Space is approximately $2.9 million. The base rent increases approximately 3.5% in each subsequent year of the Lease Term. The Lease also provides for rent abatement of approximately $1.8 million and $2.0 million for the first year of the Lease Term for the Original Space and Expansion Space, respectively. The Company has a one-time improvement allowance of $5.7 million for the Tenant Improvements (the "Original Allowance"). The Landlord disbursed the Original Allowance for the Tenant Improvement on behalf of the Company. At its election, the Company is also entitled to an additional improvements allowance of $0.9 million (“Original Additional Allowance”). Effective August 17, 2017, the Company elected to use the Original Additional Allowance and the base rent was increased by an aggregate of $1.7 million over the Lease Term. As of December 31, 2017, the Company has recorded $6.6 million of leasehold improvements under property, plant and equipment, net related to costs incurred under the Original Allowance and the Original Additional Allowance. The Lease Amendment provides for a one-time improvement allowance of $1.0 million for certain tenant improvements and, at its election, the Company is also entitled to an additional improvements allowance of $1.5 million (“Expansion Additional Allowance”). In the event the Company elects to use the Expansion Additional Allowance, the base rent will be increased as calculated in the Lease Amendment. Pursuant to the Lease Amendment, the Company holds the option to pay the balance of the Original Additional Allowance and Expansion Additional Allowance in full any time within the first 36 months of the Lease Term. Future minimum lease payments under the operating leases as of December 31, 2017 are as follows (in thousands): Year Ending December 31, Amounts 2018 $ 4,028 2019 6,201 2020 6,418 2021 6,645 2022 6,877 Thereafter 38,780 Total minimum lease payments $ 68,949 The Company recognizes rent expense on a straight-line basis over the non-cancelable lease period. Rent expense was $3.0 million, $0.6 million and $0.5 million for the years ended December 31, 2017, 2016 and 2015, respectively. Commercial Validation and Manufacturing Agreement In March 2017, the Company entered into a commercial validation and manufacturing agreement (the “Commercial Manufacturing Agreement”) with Hovione Limited (“Hovione”). Under the Commercial Manufacturing Agreement, Hovione has agreed to complete the validation program to validate and scale up the Company’s technology to manufacture the active pharmaceutical ingredient for plazomicin (the “Product”) and supply the Product to the Company. The Commercial Manufacturing Agreement has an initial term of seven years after the first delivery of the Product. Pursuant to the Commercial Manufacturing Agreement, if plazomicin is approved by the FDA, we have minimum quantity and minimum annual purchase commitments from Hovione depending on our requirements and the period of time following approval by the FDA. For the first three years following approval of plazomicin by the FDA, the Company is required to purchase at least 80% of its required quantity from Hovione. Following the initial three years after FDA approval, the Company is required to purchase between 40% and 66% of its required quantity from Hovione, depending on the amounts required during any such fiscal year. Contingent upon FDA’s approval of plazomicin, the Company has minimum annual purchase commitments from Hovione, beginning in 2020 through 2024. In connection with the Commercial Manufacturing Agreement, the Company executed certain work plans to carry out the validation and commercial manufacturing of plazomicin (the “Work Plans”). The Work Plans obligated the Company to make an aggregate amount of approximately $6.2 million in nonrefundable advance payments, of which $1.5 million was for the reservation of facilities and resources, plus procurement of long lead raw materials, paid in full under a separate agreement executed in July 2015. 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/or 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. Further, the Work Plans include certain terms that require the Company to compensate Hovione if it chooses to cancel the Work Plans (“Cancellation Clause”). As of December 31, 2017, $9.5 million is committed under the Cancellation Clause and the total aggregate amount of potential commitments, if all the services are rendered by Hovione, is approximately $23.7 million. As of December 31, 2017 and 2016, the Company has recorded approximately $4.3 million and $0.7 million, respectively as prepaid and other current assets and, during the years ended December 31, 2017, 2016 and 2015, has recognized $3.3 million, $1.2 million and zero, respectively, as research and development expenses, related to the Work Plans. 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 and officers. 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, 2017 and 2016.

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Borrowings	8. 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. An initial $15.0 million term loan was funded at closing on August 5, 2015, and a second $10.0 million term loan was funded on June 20, 2016. Borrowings under the term loans bear interest per annum at 6.99% plus the greater of 1% or the one-month LIBOR. Beginning on September 1, 2017 the Company was 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, 2017 2018 $ 12,500 2019 8,333 Total principal payments 20,833 Final fee due at maturity in 2019 2,000 Total principal and final fee payments 22,833 Unamortized discount and debt issuance costs (876 ) Total loan obligation 21,957 Less current portion (12,500 ) Loan payable, long-term $ 9,457 The obligation includes a final fee of $2.0 million, 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 $2.9 million, $2.3 million and $0.7 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	9. Stockholders' Equity 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. As of December 31, 2017, the Company had sold 1,105,549 shares of common stock under the Sales Agreement, at a weighted-average price of approximately $4.82 per share for gross proceeds of $5.3 million and net proceeds of $5.1 million after deducting the sales commissions and offering expenses. As of December 31, 2017, $24.7 million of common stock remained available to be sold under the Sales Agreement, subject to certain conditions specified therein. On December 19, 2016, the Company completed an underwritten public offering of 7,475,000 shares of its common stock at a price to the public of $13.50 per share, including the full exercise of the underwriters’ option to purchase an additional 975,000 shares of common stock. The Company received net proceeds from the offering of $94.6 million, after deducting the underwriting discounts and commissions and estimated offering expenses. On May 31, 2017, the Company completed an underwritten public offering of 5,750,000 shares of its common stock at a price to the public of $22.50 per share, including the closing of the full exercise of the underwriters’ option to purchase an additional 750,000 shares of common stock on June 9, 2017. The Company received net proceeds from the offering of $121.2 million, after deducting the underwriting discounts and commissions and offering expenses. Warrants During 2012 and 2011, the Company issued warrants to Oxford Finance LLC and Silicon Valley Bank (“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 warrants were issued in connection with a loan and security agreement, which was repaid in full in June 2014. 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. During the year ended December 31, 2017, SVB elected a net exercise of 12,510 warrants to purchase 5,896 shares of common stock. On June 3, 2016, the Company sold 7,999,996 shares of its common stock and warrants to purchase 1,999,999 shares of its common stock pursuant to the Purchase Agreement for aggregate gross proceeds of $25.4 million in the Private Placement. The warrants have an exercise price of $3.66 per share and are exercisable up to five years from the date of issuance. The Company's Chief Executive Officer, a related party, participated in the Private Placement by purchasing 141,453 shares of common stock and a warrant to purchase 35,363 shares of common stock for an aggregate purchase price of $0.5 million. Issuance costs of $0.3 million were offset against equity as a reduction from gross proceeds. At the close of the Private Placement, the estimated fair values of the common stock and warrants issued were $22.9 million and $2.6 million, respectively. As of December 31, 2017, the following warrants to purchase shares of common stock were outstanding and exercisable: Warrant Holder Issue Date In Connection With Warrant to Purchase Shares Exercise Price Expiration Date Oxford Finance LLC 4/30/2012 Loan agreement Common stock 11,676 $ 11.99 11/1/2021 Oxford Finance LLC 11/1/2011 Loan agreement Common stock 5,838 $ 11.99 11/1/2021 Growth Equity Opportunities Fund IV, LLC 6/3/2016 Private Placement Common stock 1,178,782 $ 3.66 6/3/2021 1,196,296

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plans	10. 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 unit awards (“RSUs”) and other stock-based awards for the purchase of common stock. Effective January 1, 2017, the compensation committee of the board of directors approved an evergreen increase of 1,425,522 shares of common stock that may be granted in accordance with the terms of the 2014 Plan. As of December 31, 2017, 850,639 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 year 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. As of December 31, 2017, a total of 2,050,000 shares of common stock have been authorized under the Inducement Plan, including the additional 450,000 shares that became available resulting from an amendment adopted by the board of directors as of September 13, 2017. As of December 31, 2017, 116,439 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. Effective January 1, 2017, the compensation committee of the board of directors approved an evergreen increase of 178,190 shares that may be granted in accordance with the terms of the ESPP. As of December 31, 2017, 411,716 shares of common stock have been issued to employees participating in the ESPP, and 274,951 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 in March 2014, 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. The 2003 Plan allows for early exercise of certain options prior to vesting. Upon termination of employment, the unvested shares are subject to repurchase at the original exercise price. Stock options granted or modified after March 21, 2002, that are subsequently exercised for cash prior to vesting, are not deemed to be issued until those shares vest. As of December 31, 2017 and 2016 there were no shares subject to repurchase relating to the early exercise of options. 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, 2017, a total of 829,586 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, 2017, 2016 and 2015, was classified as follows (in thousands): Year Ended December 31, 2017 2016 2015 Research and development $ 6,340 $ 2,165 $ 1,404 General and administrative 7,312 1,682 1,579 Total $ 13,652 $ 3,847 $ 2,983 Stock-based compensation expense for the year ended December 31, 2017 includes $0.7 million of expense that relates to the stock options and restricted stock units held by the former Chief Medical Officer, which were modified upon his resignation in March 2017. A summary of stock option activity is as follows: Outstanding Options Shares Available for grant Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Balance, January 1, 2015 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 $ 293 Additional shares reserved 1,235,808 — Options granted (1,477,600 ) 1,477,600 $ 4.10 Options exercised — (14,190 ) $ 4.59 $ 89 Options forfeited 310,454 (310,454 ) $ 8.19 RSUs granted (380,500 ) — RSUs cancelled 57,750 — Balance, December 31, 2016 639,374 3,540,293 $ 6.31 7.98 $ 23,837 Additional shares reserved 2,325,522 — Options granted (1,806,157 ) 1,806,157 $ 21.12 Options exercised — (227,444 ) $ 7.23 — Options forfeited 280,408 (280,408 ) $ 9.14 RSUs granted (544,185 ) — RSUs cancelled 72,116 — Balance, December 31, 2017 967,078 4,838,598 $ 11.63 7.69 $ 14,174 At December 31, 2017 Vested and exercisable 2,074,120 $ 8.25 6.41 $ 7,705 Vested and expected to vest 4,704,835 $ 11.50 7.70 $ 14,005 The following table summarizes information about stock options outstanding as of December 31, 2017: Options Outstanding Vested and Exercisable Exercise Price Number of Options Weighted-Average Remaining Contractual Life (in Years) Number of Options Weighted-Average Exercise Price $3.41 - $3.68 502,764 7.84 213,306 $ 3.65 $3.75 - $4.44 594,704 8.61 211,184 $ 4.28 $4.62 - $5.86 608,616 7.24 404,603 $ 5.18 $6.60 - $7.26 722,468 4.89 534,692 $ 7.03 $8.04 - $10.44 508,994 6.19 379,275 $ 9.17 $10.98 - $16.18 528,793 8.44 148,841 $ 12.41 $17.55 - $22.93 416,950 9.32 38,527 $ 22.08 $23.62 - $23.62 792,084 9.12 143,692 $ 23.62 $23.68 - $23.68 130,000 9.16 0 $ — $24.71 - $24.71 33,225 9.39 0 $ — 4,838,598 7.69 2,074,120 $ 8.25 Stock Options Granted to Employees and Non-Employee Directors During the years ended December 31, 2017, 2016 and 2015, the Company granted stock options to employees and directors to purchase 1,806,157, 1,477,600 and 929,100 shares, respectively, of common stock under the stock plans with a weighted-average estimated grant-date fair value of $21.12, $4.10 and $5.02 per share, respectively. As of December 31, 2017, there were unrecognized compensation costs of $22.2 million related to outstanding employee and non-employee director stock options, which are expected to be recognized over a weighted-average period of 2.95 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 estimated grant date fair value of employee stock options with time-based vesting terms was calculated using the Black-Scholes valuation model, based on the following assumptions: Year Ended December 31, 2017 2016 2015 Expected term 5.0 – 6.0 years 5.3 – 6.0 years 5.4 – 6.0 years Expected volatility 78 - 81% 67 – 74% 65 – 75% Risk-free interest rate 1.7 – 2.3% 1.1 – 1.9% 1.5 – 1.9% Expected dividend yield —% —% —% 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. Stock Options and Restricted Stock Units Granted to Non-Employees During the years ended December 31, 2017 and 2016, the Company granted to non-employees an option to purchase 3,000 and 15,000 shares of common stock, respectively, and 1,500 and zero RSUs, respectively, that vest upon achievement of certain performance-based targets. The Company did not grant stock options or restricted stock units to non-employees during the year ended December 31, 2015. The Company recorded non-employees stock-based compensation expense of approximately $0.5 million and $0.1 million for the years ended December 31, 2017and 2016. The Company measures the estimated fair value of the award for each period until the award is fully vested. The fair value of options granted to non-employees during the years ended December 31, 2017 and 2016 was estimated using Black-Scholes with the following assumptions: Year Ended December 31, 2017 2016 Expected term 0.25 – 9.39 years 0.8 – 1.0 years Expected volatility 48 - 80% 63 – 125% Risk-free interest rate 0.9 – 2.4% 0.6 – 0.9% Expected dividend yield —% —% Restricted Stock Units Granted to Employees During the years ended December 31, 2017, 2016 and 2015, the Company granted restricted stock units (“RSUs”) to employees to purchase 544,185, 380,500 and 291,525 shares of common stock, respectively, under the stock plans with a weighted-average estimated grant-date fair value of $20.61, $4.01 and $7.76 per share, respectively. RSUs generally vest annually over a 4-year service period and vesting is contingent on continued service. As of December 31, 2017, there were unrecognized compensation costs of $11.0 million related to outstanding RSUs, which are expected to be recognized over a weighted-average period of 2.74 years. A summary of RSU activity is as follows: RSU Awards Outstanding Number of Shares Weighted-Average Grant Date Fair Market Value Aggregate Intrinsic Value (in thousands) 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 RSUs granted 380,500 $ 4.01 RSUs released (89,722 ) $ 8.22 RSUs cancelled (57,750 ) $ 6.71 Balance, December 31, 2016 605,052 $ 5.60 $ 7,878 RSUs granted 544,185 $ 20.61 RSUs released (185,889 ) $ 6.24 RSUs cancelled (72,116 ) $ 9.22 Balance, December 31, 2017 891,232 $ 14.34 $ 9,572 Stock Options and Restricted Stock Units Granted to Employees that Contain Performance Conditions During the years ended December 31, 2017, 2016 and 2015, the Company granted options to purchase an aggregate of 184,200, 354,250 and zero shares of common stock, respectively, that vest upon the achievement of market-based common stock targets. During the years ended December 31, 2017, 2016 and 2015, the Company granted 35,050, 59,925 and zero RSUs, respectively, that vest 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 (“Monte-Carlo”), which requires the use of a range of assumptions. The expected life assumption is not used in the Monte-Carlo simulation model, but the output of the model indicates an expected term. The associated stock-based compensation expense is being recognized on a straight-line basis over the implicit service period (expected time to vest) derived from that simulation model. The fair value of awards granted to non-employees was estimated using Monte-Carlo with the following assumptions: Year Ended December 31, 2017 2016 Expected term 0.5–3.5 years 2.2–6.0 years Expected volatility 75-80% 70% Risk-free interest rate 2.1–2.4% 1.4%–2.3% Expected dividend yield —% —%

Contingently Redeemable Common

Contingently Redeemable Common Stock	12 Months Ended
	Dec. 31, 2017
Temporary Equity Disclosure [Abstract]
Contingently Redeemable Common Stock	11. Contingently Redeemable Common Stock In May 2017, the Company entered into a Common Stock Purchase Agreement with the Gates Foundation, pursuant to which the Company agreed to sell 407,331 shares of its contingently redeemable common stock (the “Shares”) to the Gates Foundation in a private placement at a purchase price per share equal to $24.55, for gross proceeds to the Company of $10.0 million (the “Gates Investment”). In connection with the Gates Investment, the Company entered into the Letter Agreement, which includes terms of Global Access Commitments (see Note 1). Under the Letter Agreement, if the Company defaults in its obligation to conduct certain mutually-agreed upon work, use the proceeds from the Gates Investment as described in the Letter Agreement, or otherwise triggers certain other events of default as described in the Letter Agreement (“Charitable Default”), subject to a cure period, the Gates Foundation will have the right to request that (a) the Company redeem, or facilitate the purchase by a third party of, the Shares then held by the Gates Foundation at a price per share equal to the greater of (i) the fair market value of the common stock (if the Shares are freely tradable, the closing price of the Company’s common stock on the trading day prior to the redemption or purchase, as applicable), or (ii) an amount equal to $24.55 plus a compounded annual return of 5% from the date of issuance of the Shares, or (b) if the Shares then held by the Gates Foundation are not freely tradeable, the Company register the resale of the Shares held by the Gates Foundation on an effective registration statement, subject to certain conditions and qualifications. The Company concluded that certain potential events of the Charitable Default are not solely within the control of the Company and, accordingly, has classified the Shares outside of permanent equity, as temporary equity (“Mezzanine Equity”). The 407,331 shares classified as Mezzanine Equity were recorded as contingently redeemable common stock at an initial carrying value equal to the gross proceeds of approximately $10.0 million, which approximated their fair value at the date of issuance. The Company has determined that the 407,331 shares of contingently redeemable common stock are not currently redeemable and that a Charitable Default is not currently probable. If, and at the time when, a Charitable Default becomes probable, then the Company will record a change in the carrying value to adjust it to the redemption value of the contingently redeemable common stock. At the time of such an occurrence, the contingently redeemable common stock will be adjusted to equal the redemption value at the end of each reporting period.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2017, 2016 and 2015 is as follows: Year Ended December 31, 2017 2016 2015 Statutory tax rate 34.00 % 34.00 % 34.00 % State taxes, net of federal benefits 1.38 % 0.96 % -3.62 % Stock-based compensation -0.16 % -0.62 % -1.20 % Credits 1.99 % 1.46 % 3.30 % Other -0.64 % -0.10 % -0.54 % Valuation allowance -4.03 % -26.22 % -31.94 % Warrant valuation 0.00 % -9.48 % 0.00 % Tax rate change -32.54 % 0.00 % 0.00 % Effective tax rate 0.00 % 0.00 % 0.00 % The tax effects of temporary differences and carryforwards that give rise to the Company’s deferred tax assets are as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss carry forwards $ 68,807 $ 71,858 Research and development credit 17,365 10,969 Intangible assets 824 1,653 Depreciation — 191 Temporary differences 8,017 4,682 Gross Deferred tax assets 95,013 89,353 Less: valuation allowance (95,013 ) (89,353 ) 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 $5.7 million and $18.7 million during the years ended December 31, 2017 and 2016, respectively. The Company had federal and state net operating loss carryforwards of approximately $297.5 million and $85.0 million, respectively, at December 31, 2017. 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 2018, respectively. The Company also had federal and state research and development credit carryforwards of approximately $13.8 million and $7.2 million, respectively, at December 31, 2017. 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, 2017 2016 2015 Balance at beginning of year $ 1,197 $ 957 $ — Increase related to current year tax provision 516 240 162 Increase related to tax rate change 144 — — Increase related to prior year tax provision — — 795 Balance at end of year $ 1,857 $ 1,197 $ 957 The unrecognized tax benefits, if recognized and in absence of full valuation allowance, would impact the income tax provision by $1.7 million, $1.0 million and $0.8 million as of December 31, 2017, 2016 and 2015, respectively. 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, 2017. On December 22, 2017, the Tax Cuts and Jobs Act (the “Act”) was enacted into law in the United States. The Act reduces the U.S. federal corporate tax rate from 35% to 21%, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. As of December 31, 2017, the Company has not completed the accounting for the tax effects as a result of the Act. However, the Company has made a reasonable estimate of the effects on its existing deferred tax balances and recognized a provisional amount of $40.9 million. In some cases, the Company has not been able to make a reasonable estimate and continues to account for those items based on our existing accounting under ASC 740, Income Taxes, Pursuant to SEC Staff Accounting Bulletin (SAB) 118 (regarding the application of ASC 740 associated with the enactment of the Act), the Company remeasured certain tax assets and liabilities based on the rates the Company expects them to reverse in the future, which is generally 21%. The Company is still analyzing certain aspects of the ACT and refining its calculations, which could potentially affect the measurement of these balances or give rise to new deferred tax amounts. The provisional amount recorded related to the remeasurement of the deferred tax balance was $40.9 million, which was fully offset by a valuation allowance.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plan	13. 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 changed the plan to increase its 401(k) match to 50% of employees' contributions, up to 8% of annual earnings, starting in January 2016. The Company's contributions were $0.9 million, $0.5 million and $0.3 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related-Party Transactions	14. Related-Party Transactions In June 2016, the Company sold 7,999,996 shares of its common stock and warrants to purchase 1,999,999 shares of its common stock pursuant to the Purchase Agreement for aggregate gross proceeds of $25.4 million in the Private Placement. The warrants have an exercise price of $3.66 per share and are exercisable up to five years from the date of issuance. A trust affiliated with the Company's Chief Executive Officer, a related party, participated in the Private Placement by purchasing 141,453 shares of common stock and a warrant to purchase 35,363 shares of common stock for an aggregate purchase price of approximately $0.5 million. In August 2017, the Company’s Chief Executive Officer, a related party, exercised these warrants to purchase 35,363 shares of common stock. The Company received $129,429 in proceeds from these warrant exercises. For further detail of the warrants issued in connection with the Private Placement, refer to Note 3.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events In January 2018, pursuant to the Sales Agreement with Cowen, the Company recommenced the ATM equity program under which Cowen has acted as a sales agent. In January and February 2018, the Company sold 2,144,454 shares of common stock at a weighted-average price of approximately $11.51 per share for gross proceeds of $24.7 million and net proceeds of $24.0 million after deducting the sales commissions and offering expenses. As of February 27, 2018, no shares remain available for sale under the Sales Agreement. On February 26, 2018 (the “Closing Date”), the Company entered into a loan and security agreement (the “Loan Agreement”) with Silicon Valley Bank. The Loan Agreement provides for (i) a $25.0 million Term A loan facility with a maturity of five years (the “Term A Loan”) and (ii) an up to $25.0 million Term B loan facility, which may be drawn, subject to certain conditions, by the Company during the first 12 months after the Closing Date ( the “Term B Loans” and together with the Term A Loan, the “Term Loans”). Each Term B Loan has a maturity of four years. Borrowings under the Term A Loan bear interest at a floating per annum rate equal to the greater of (a) the prime rate minus 1.50% and (b) 3.00%, and the Term B Loans bear interest through maturity at a floating per annum rate equal to the greater of (a) 1.00% above the prime rate and (b) 5.50%. In addition to paying interest on outstanding principal, the Company will be required to pay an unused Term B Loan fee of 1.00% of the commitments under the Term B Loans if the Company does not borrow any Term B Loans. The Company is permitted to make interest-only payments on the Term A Loan through February 2020 and the Term B Loans for the first twenty-four (24) months following the funding date of each respective Term B Loan after which the Company will be required to repay the Term A Loan in 36 consecutive equal monthly installments of principal and repay any Term B Loans in 24 consecutive equal monthly installments of principal. The Company is obligated to pay a fee equal to 6.00% of the funded Term Loans upon the earliest to occur of the maturity date, the prepayment or repayment of such Term Loans or the termination of the Loan Agreement. 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. The Company is required to have cash on deposit at Silicon Valley Bank equal to the greater of (a) $48.0 million and (b) the “Monthly Cash Burn,” which is defined as the difference of (1)(i) net loss plus (ii) unfinanced capital expenditures minus (2)(i) depreciation and amortization expenses, (ii) non-cash stock compensation expense and (iii) other non-cash expenses as approved by Silicon Valley Bank. If at any time the Company’s aggregate balances at Silicon Valley Bank are less than the foregoing, the Company is required to deposit at Silicon Valley Bank cash collateral in an amount equal to the outstanding Term A Loan. The Term Loans are secured by substantially all of the Company’s assets, except for its intellectual property which is subject to a negative pledge and certain other customary exclusions. On February 26, 2018, the Company terminated the Loan and Security Agreement dated August 5, 2015 with Solar Capital Ltd. and repaid $20.9 million of the outstanding principal and interest. On February 27, 2018, the Company filed an amended Registration Statement on Form S-3 (the “2018 Shelf Registration Statement”) covering the offering of up to $250.0 million of common stock, preferred stock, debt securities, warrants and units. In addition, on February 27, 2018, the Company filed a prospectus supplement to the 2018 Shelf Registration Statement covering the offering, issuance and sale of up to $50.0 million shares of its common stock in ATM offerings pursuant to a Common Stock Sales Agreement entered into with Cowen and Company, LLC on February 27, 2018.

Selected Unaudited Quarterly Fi

Selected Unaudited Quarterly Financial Data	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Unaudited Quarterly Financial Data	16. 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 2017 and 2016 (in thousands, except per share amounts): Three Months Ended December 31, 2017 September 30, 2017 June 30, 2017 March 31, 2017 Contract revenue 1,869 577 1,266 7,463 Operating expenses 43,973 37,121 31,059 25,348 Other income (expense), net 5,722 6,637 3,723 (15,374 ) Net loss (36,382 ) (29,907 ) (26,070 ) (33,259 ) Net loss per common share: Basic (0.86 ) (0.71 ) (0.68 ) (0.93 ) Diluted (0.98 ) (0.85 ) (0.78 ) (0.93 ) Weighted-average shares used to calculate net loss per common share: Basic 42,422,592 42,259,001 38,072,763 35,725,876 Diluted 43,257,602 43,211,059 39,092,279 35,725,876 Three Months Ended December 31, 2016 September 30, 2016 June 30, 2016 March 31, 2016 Contract revenue 10,734 16,046 9,144 5,849 Operating expenses 22,796 24,996 25,659 17,670 Other income (expense), net (17,662 ) (2,088 ) (1,753 ) (376 ) Net loss (29,724 ) (11,038 ) (18,268 ) (12,197 ) Net loss per common share: Basic (1.04 ) (0.41 ) (0.87 ) (0.66 ) Diluted (1.04 ) (0.41 ) (0.87 ) (0.66 ) Weighted-average shares used to calculate net loss per common share: Basic 28,653,045 26,789,397 20,899,297 18,398,288 Diluted 28,653,045 26,789,397 20,899,297 18,398,288 (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 Accoun24

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Reclassifications	Reclassifications The change in derivative liability on the consolidated statements of operations for the year ended December 31, 2015 has been reclassified to be included in the change in warrant and derivative liabilities to conform to the current year’s presentation. Such reclassifications did not impact the Company’s net loss or financial position. The cash and cash equivalents on the condensed consolidated statements of cash flows for the year ended December 31, 2015 has been reclassified to include restricted cash to conform to the current period’s presentation. Such reclassification did not impact the Company’s net loss or financial position.
Basis of Presentation and Consolidation	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, 2017, 2016 and 2015.
Liquidity and Going Concern	Liquidity and Going Concern 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 the Company’s 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, 2017, the Company had sold 1,105,549 shares pursuant to its ATM equity offering program at a weighted-average price of $4.82 per share for aggregate offering proceeds of $5.3 million and aggregate net proceeds of $5.1 million, after deducting the sales commissions and offering expenses. On June 3, 2016, the Company sold 7,999,996 shares of its common stock and warrants to purchase 1,999,999 shares of its common stock pursuant to Securities Purchase Agreement (the "Purchase Agreement") for aggregate gross proceeds of $25.4 million and aggregate net proceeds of $25.1 million, after deducting the issuance costs, in connection with a private placement financing transaction (the "Private Placement"). The warrants have an exercise price of $3.66 per share and are exercisable up to five years from the date of issuance. On December 19, 2016, the Company completed an underwritten public offering of common stock made under a prospectus supplement and related prospectus pursuant to the Shelf Registration Statement. This offering resulted in the sale of 7,475,000 shares, at a price of $13.50 per share, including the full exercise of the underwriter’s option to purchase an additional 975,000 shares of common stock. The Company received net proceeds from the offering of $94.6 million, after deducting the underwriting discounts and commissions and estimated offering expenses. On May 4, 2017, the Company entered into an agreement with the Bill & Melinda Gates Foundation (the “Gates Foundation”) to discover drug candidates against gram-negative bacterial pathogens intended to prevent neonatal sepsis (the “Grant Agreement”). Pursuant to the Grant Agreement, the Gates Foundation awarded the Company up to approximately $10.5 million in grant funding (“Grant Funds”) over a three-year research term, of which approximately $3.2 million was received in May 2017 (the “Advance Funds”). Concurrently with the Grant Agreement, the Company entered into a Common Stock Purchase Agreement (the “Gates Purchase Agreement”) with the Gates Foundation, pursuant to which the Company agreed to sell 407,331 shares of its contingently redeemable common stock to the Gates Foundation in a private placement at a purchase price per share equal to $24.55, for gross proceeds to the Company of $10.0 million (“Gates Investment”). In connection with the Grant Agreement and the Gates Investment, the Company entered into a strategic relationship with the Gates Foundation (the “Letter Agreement”). Under the terms of the Letter Agreement, the Gates Investment and Grant Funds may only be used to conduct mutually agreed upon work, including the scale up of the Company’s antibody platform technology to launch a product intended to prevent neonatal sepsis (the “NSP”). Pursuant to the Letter Agreement, the Company agreed to make the NSP available and accessible in certain developing countries and to grant the Gates Foundation a non-exclusive license to commercialize selected drug candidates in certain developing countries, which may only be exercised in the event of certain defaults as described in the Letter Agreement (the “Global Access Commitments”). The Global Access Commitments will continue in effect until the earlier of 25 years from the closing of the Gates Investment or 7 years following the termination of all funding provided by the Gates Foundation; provided, that the Global Access Commitments will continue for any products or services developed with funding provided by the Gates Foundation which continue to be developed or available in certain developing countries. On May 31, 2017, the Company completed an underwritten public offering of 5,750,000 shares of its common stock at a price to the public of $22.50 per share, including the closing of the full exercise of the underwriters’ option to purchase an additional 750,000 shares of common stock on June 9, 2017. The Company received net proceeds from the offering of $121.2 million, after deducting the underwriting discounts and commissions and offering expenses. In September 2017, the Company was awarded a contract (“C-Scape Contract”) valued at up to $18.0 million in grant funding from the Biomedical Advanced Research and Development Authority (“BARDA”) to support the development of C-Scape. The C-Scape Contract includes a base period with committed funding of $12.0 million and subsequent option periods that, if exercised, would bring the total value of the award to $18.0 million. The Company has incurred losses and negative cash flows from operations every year since its inception. As of December 31, 2017, the Company had unrestricted cash, cash equivalents and short-term investments of approximately $164.8 million and an accumulated deficit of approximately $372.8 million. Management expects that, based on its current operating plans, the Company’s existing cash, cash equivalents and short-term investments will be sufficient to fund its current planned operations for at least the next twelve months from the issuance of this report. Management plans to raise additional funds through equity or debt financing arrangements, government contracts, and/or third-party collaboration funding in the future to fund its operations, including the commercial launch of plazomicin. 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 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.
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 and warrant 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, 2017 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 amount of the loan payable approximates its fair value. The warrant and derivative liabilities are recorded at estimated fair value with changes in estimated fair value recorded in the Company’s statements of operations.
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. As of December 31, 2017 and 2016, cash and cash equivalents consisted of bank deposits, cash, commercial paper, money market funds, cash repurchase agreement investments and overnight cash sweep investments in government money market funds.
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 As of December 31, 2017 and 2016, the Company had restricted cash of $9.7 million and $0.4 million, respectively. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheet that sum to the total of the same such amounts shown in the consolidated statements of cash flows (in thousands): Year Ended December 31, 2017 2016 2015 Cash and cash equivalents $ 145,219 $ 118,964 $ 20,287 Restricted cash, current 5,891 127 - Restricted cash, non-current 3,855 250 127 Total cash, cash equivalents, and restricted cash $ 154,965 $ 119,341 $ 20,414 In May 2017, the Company received $13.2 million of funding from the Gates Foundation from the Grant Funds and Gates Investment (see Note 1). The Letter Agreement restricts the Company’s use to expenditures that are reasonably attributable to the activities required to support the research projects funded by the Gates Foundation, including an allocation of overhead and administrative expenses. As of December 31, 2017 and 2016 the Company had $9.2 million and zero, respectively, of restricted cash related to the unspent cash provided by the Gates Foundation. The remaining restricted cash serves as collateral for the letters of credit provided as security deposits under the Company’s facility lease and expire approximately 90 days from the end of their respective lease terms. As of December 31, 2017 and 2016, the Company had $0.5 million and $0.4 million, respectively, of restricted cash, which relates to the Company’s facility leases.
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 regarding resource allocation and assessing performance. The Company has one operating segment.
Customer Concentration	Customer Concentration For the years ended December 31, 2017, 2016 and 2015, all of the Company’s revenue has been generated from funding pursuant to U.S. government contracts and a non-profit foundation grant. 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 with balances that generally 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. The Company’s 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, 2017 and 2016, the Company has not experienced any credit losses in such accounts or investments.
Contracts Receivable	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, 2017 and 2016, as the Company expects full collection of the receivable balances.
Property and Equipment, Net	Property and Equipment, Net Property and equipment consist of office equipment, laboratory equipment, and leasehold improvements and are 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 seven 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. For the years ended December 31, 2017, 2016 and 2015, the Company did not have any impairment charges.
Warrant Liability	Warrant Liability On June 3, 2016, the Company issued warrants to purchase 1,999,999 shares of its common stock in connection with the Private Placement. Each warrant has an exercise price of $3.66 per share and is exercisable for five years from the date of issuance. The Company accounts for these warrants as a liability instrument measured at estimated fair value. The initial fair value of the warrants was determined using a calibration model that involved the Black-Scholes Pricing Model ("Black-Scholes"), which requires inputs such as the risk-free interest rate, expected share price volatility, underlying price per share of the Company's common stock and remaining term of the warrants. The warrants are subject to remeasurement at each balance sheet date, using Black-Scholes, with any changes in the fair value of the outstanding warrants recognized in the condensed consolidated statements of operations. As of December 31, 2017, warrants to purchase 1,178,782 shares of the Company’s common stock remain outstanding and unexercised.
Contingently Redeemable Common Stock	Contingently Redeemable Common Stock In May 2017, the Company agreed to sell 407,331 shares of its contingently redeemable common stock to the Gates Foundation in a private placement at a purchase price per share equal to $24.55 (see Note 1). Common stock with embedded redemption features that are settled at the option of the holder, are considered redeemable common stock. Redeemable common stock is considered to be temporary equity and presented in a section between liabilities and equity on the Company’s consolidated balance sheets. Subsequent adjustment of the amount presented in temporary equity is required only if the Company determines that it is probable that the instrument will become redeemable. Upon termination of the redemption features, the redeemable common stock is reclassified into equity. As of December 31, 2017, 407,331 shares of contingently redeemable common stock remain as temporary.
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 2017 and 2016, 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 from government contracts and a non-profit foundation grant. Government contracts 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 or grant arrangements are recorded as revenue if the Company is deemed to be the principal participant in the arrangements because the activities under the contracts or grants are part of the Company’s development programs. If the Company is not the principal participant, the funds from contracts or grants are recorded as a reduction to research and development expense. Contract funds received are not refundable and are recognized when the related qualified research and development costs are incurred and there is reasonable assurance that the funds will be received. Funds received in advance are recorded as deferred revenue. Management has determined that the Company is the principal participant under the Company’s government contract arrangements and non-profit grant agreement, and accordingly, the Company records amounts earned under these arrangements as 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, non-profit grants 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 recognized as an expense as the goods are delivered or the related services are performed. For certain research and development services where the Company has not yet been invoiced or otherwise notified of actual cost from the third-party contracted service providers, the Company is required to estimate the extent of the services that have been performed on the Company’s behalf and the associated costs incurred at each reporting period. The majority of the service providers invoice the Company monthly in arrears for services performed. The Company make estimates of the accrued expenses as of each balance sheet date in the consolidated financial statements based on facts and circumstances known to the Company at that time. The Company periodically confirms the accuracy of the estimates with the service providers and makes adjustments if necessary. Examples of estimated accrued research and development expenses include services from: • contract research organizations (“CROs”) and other service providers in connection with clinical studies; • contract manufacturers in connection with the production of clinical trial materials; and • vendors in connection with preclinical development activities. The Company bases the expenses related to preclinical studies and clinical trials on estimates of the services received and efforts expended pursuant to contracts with multiple research institutions and CROs that conduct and manage such studies and trials on the Company’s behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract, and may result in uneven payment flows and expense recognition. Payments under some of these contracts depend on factors such as the successful enrollment of patients and the completion of clinical trial milestones. In accruing service fees, the Company estimates the time period over which these services will be performed and the level of effort to be expended and costs to be incurred during each reporting period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company adjusts the accrual accordingly. The Company’s estimation of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in reporting changes in estimates in any particular period. To date, there have been no material adjustments from the Company’s estimates to the amount actually incurred.
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. The Company assesses the need for a valuation allowance against the Company’s deferred income tax assets by considering both positive and negative evidence related to whether it is more likely than not that the deferred income tax assets will be realized. In evaluating its ability to recover the deferred income tax assets within the jurisdiction from which they arise, the Company considered all available positive and negative evidence, including scheduled reversals of deferred income tax liabilities, projected future taxable income, tax-planning strategies, and results of recent operations. Due to the Company’s considerations, 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. The Company has reported a net loss for the years ended December 31, 2017, 2016 and 2015, and diluted net loss per common share is the same as basic net loss per common share for those periods. The following table sets forth the computation of the basic and diluted net loss per share during the years ended December 31, 2017, 2016 and 2015 (in thousands, except share and per share amounts): Year Ended December 31, 2017 2016 2015 Net loss $ (125,618 ) $ (71,227 ) $ (27,093 ) Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share 39,645,635 23,707,063 18,147,986 Basic and diluted net loss per common share $ (3.17 ) $ (3.00 ) $ (1.49 ) The following potentially dilutive securities outstanding have been excluded from diluted net loss per share, because their effect would be antidilutive, as of December 31, 2017, 2016 and 2015: December 31, 2017 2016 2015 Options to purchase common stock 4,838,598 3,540,293 2,387,337 Restricted stock units 891,232 605,052 372,024 Warrants to purchase common stock 1,196,296 1,322,754 30,024
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which provides a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and will supersede most current revenue recognition guidance. 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 Company expects to be entitled in exchange for those goods or services. This ASU defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing GAAP. The Company expects to adopt the new revenue standard as of January 1, 2018 using the modified retrospective method. The Company has completed its assessment and determined that its government contracts and non-profit foundation grant are not in scope of ASC 606 and there is no impact on its consolidated financial statements. In March 2016, the FASB issued ASU No 2016-09, Compensation - Stock Compensation Improvements to Employee Share-Based Payment Accounting In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheet that sum to the total of the same such amounts shown in the consolidated statements of cash flows (in thousands): Year Ended December 31, 2017 2016 2015 Cash and cash equivalents $ 145,219 $ 118,964 $ 20,287 Restricted cash, current 5,891 127 - Restricted cash, non-current 3,855 250 127 Total cash, cash equivalents, and restricted cash $ 154,965 $ 119,341 $ 20,414
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, 2017, 2016 and 2015 (in thousands, except share and per share amounts): Year Ended December 31, 2017 2016 2015 Net loss $ (125,618 ) $ (71,227 ) $ (27,093 ) Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share 39,645,635 23,707,063 18,147,986 Basic and diluted net loss per common share $ (3.17 ) $ (3.00 ) $ (1.49 )
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 diluted net loss per share, because their effect would be antidilutive, as of December 31, 2017, 2016 and 2015: December 31, 2017 2016 2015 Options to purchase common stock 4,838,598 3,540,293 2,387,337 Restricted stock units 891,232 605,052 372,024 Warrants to purchase common stock 1,196,296 1,322,754 30,024

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
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, 2017: December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Assets Level 1: Restricted cash 9,746 — — 9,746 Money market funds 58,769 — — 58,769 U.S. Treasury bills 4,992 — — 4,992 Subtotal 73,507 — — 73,507 Level 2: Commercial paper 46,040 — — 46,040 U.S. agency securities 4,990 — — 4,990 Other debt securities 50,000 — — 50,000 Subtotal 101,030 — — 101,030 Total $ 174,537 $ — $ — $ 174,537 Reported as: Cash and cash equivalents $ 145,219 Short-term investments $ 19,572 Restricted cash $ 9,746 Liabilities, Level 3 Warrant Liability $ 9,774 Derivative Liability $ 686 Total $ 10,460 As of December 31, 2016: December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Assets Cash $ 3,728 $ — $ — $ 3,728 Level 1: Restricted cash 377 — — 377 Money market funds 115,236 — — 115,236 Subtotal 115,613 — — 115,613 Level 2: Corporate debt securities 12,969 — (7 ) 12,962 Commercial paper 13,950 — — 13,950 Subtotal 26,919 — (7 ) 26,912 Total $ 146,260 $ — $ (7 ) $ 146,253 Reported as: Cash and cash equivalents $ 118,964 Short-term investments $ 26,912 Restricted cash $ 377 Liabilities, Level 3 Warrant liability $ 13,874 Derivative liability $ 602 Total $ 14,476
Schedule of Assumptions Used	The estimated fair values of the warrants were determined using Black-Scholes with the following assumptions, during the years ended December 31, 2017 and 2016: December 31, 2017 December 31, 2016 Expected volatility 80% 60 - 80% Expected term 3.4 - 4.3 years 4.4 - 5.0 years Risk-free interest rate 1.6 - 2.0% 1.0 - 1.9% Dividend yield —% —%
Changes in Estimated Fair Value of Liabilities Measurements	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 December 31, 2017, 2016 and 2015 (in thousands): Estimated Fair Value of Derivative Liability Estimated Fair Value of Warrant Liability Balance of Level 3 Liabilities at December 31, 2014 $ — $ — Estimated fair value of derivative liability issued 356 — Change in estimated fair value of derivative liability 19 — Balance of Level 3 Liabilities at December 31, 2015 375 — Estimated fair value of warrants issued — 2,579 Change in estimated fair value of warrant liability — 19,632 Reclassification of warrant liability to additional paid-in-capital upon exercise of warrants — (8,337 ) Change in estimated fair value of derivative liability 227 — Balance of Level 3 Liabilities at December 31, 2016 602 13,874 Change in estimated fair value of warrant liability — (2,012 ) Reclassification of warrant liability to additional paid-in-capital upon exercise of warrants — (2,088 ) Change in estimated fair value of derivative liability 84 — Balance of Level 3 Liabilities at December 31, 2017 $ 686 $ 9,774

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Schedule of Prepaids and Other Current Assets	Prepaids and other current assets consisted of the following (in thousands): December 31, 2017 December 31, 2016 Deferred research and development costs $ 4,317 $ 660 Prepaid expenses 1,755 1,390 Other current assets 295 139 $ 6,367 $ 2,189
Schedule of Property and Equipment	Property and equipment, net consisted of the following (in thousands): December 31, 2017 2016 Office equipment $ 863 $ 644 Laboratory equipment 6,663 4,038 Leasehold improvements 9,355 1,072 Construction-in-progress 1,040 1,896 Property and equipment, gross 17,921 7,650 Less: accumulated depreciation (3,111 ) (4,389 ) Property and equipment, net $ 14,810 $ 3,261
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): December 31, 2017 2016 Accrued clinical and development expenses $ 6,480 $ 3,681 Payroll and related bonus expenses 6,281 4,941 Other 2,680 1,076 $ 15,441 $ 9,698

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments	Future minimum lease payments under the operating leases as of December 31, 2017 are as follows (in thousands): Year Ending December 31, Amounts 2018 $ 4,028 2019 6,201 2020 6,418 2021 6,645 2022 6,877 Thereafter 38,780 Total minimum lease payments $ 68,949

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Future Minimum Debt Obligation Payments	Future principal debt payments on the loan payable are as follows (in thousands): December 31, 2017 2018 $ 12,500 2019 8,333 Total principal payments 20,833 Final fee due at maturity in 2019 2,000 Total principal and final fee payments 22,833 Unamortized discount and debt issuance costs (876 ) Total loan obligation 21,957 Less current portion (12,500 ) Loan payable, long-term $ 9,457

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Stockholders' Equity Note, Warrants or Rights	As of December 31, 2017, the following warrants to purchase shares of common stock were outstanding and exercisable: Warrant Holder Issue Date In Connection With Warrant to Purchase Shares Exercise Price Expiration Date Oxford Finance LLC 4/30/2012 Loan agreement Common stock 11,676 $ 11.99 11/1/2021 Oxford Finance LLC 11/1/2011 Loan agreement Common stock 5,838 $ 11.99 11/1/2021 Growth Equity Opportunities Fund IV, LLC 6/3/2016 Private Placement Common stock 1,178,782 $ 3.66 6/3/2021 1,196,296

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2017
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, 2017, 2016 and 2015, was classified as follows (in thousands): Year Ended December 31, 2017 2016 2015 Research and development $ 6,340 $ 2,165 $ 1,404 General and administrative 7,312 1,682 1,579 Total $ 13,652 $ 3,847 $ 2,983
Summary of Stock Option Activity	A summary of stock option activity is as follows: Outstanding Options Shares Available for grant Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Balance, January 1, 2015 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 $ 293 Additional shares reserved 1,235,808 — Options granted (1,477,600 ) 1,477,600 $ 4.10 Options exercised — (14,190 ) $ 4.59 $ 89 Options forfeited 310,454 (310,454 ) $ 8.19 RSUs granted (380,500 ) — RSUs cancelled 57,750 — Balance, December 31, 2016 639,374 3,540,293 $ 6.31 7.98 $ 23,837 Additional shares reserved 2,325,522 — Options granted (1,806,157 ) 1,806,157 $ 21.12 Options exercised — (227,444 ) $ 7.23 — Options forfeited 280,408 (280,408 ) $ 9.14 RSUs granted (544,185 ) — RSUs cancelled 72,116 — Balance, December 31, 2017 967,078 4,838,598 $ 11.63 7.69 $ 14,174 At December 31, 2017 Vested and exercisable 2,074,120 $ 8.25 6.41 $ 7,705 Vested and expected to vest 4,704,835 $ 11.50 7.70 $ 14,005
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, 2017: Options Outstanding Vested and Exercisable Exercise Price Number of Options Weighted-Average Remaining Contractual Life (in Years) Number of Options Weighted-Average Exercise Price $3.41 - $3.68 502,764 7.84 213,306 $ 3.65 $3.75 - $4.44 594,704 8.61 211,184 $ 4.28 $4.62 - $5.86 608,616 7.24 404,603 $ 5.18 $6.60 - $7.26 722,468 4.89 534,692 $ 7.03 $8.04 - $10.44 508,994 6.19 379,275 $ 9.17 $10.98 - $16.18 528,793 8.44 148,841 $ 12.41 $17.55 - $22.93 416,950 9.32 38,527 $ 22.08 $23.62 - $23.62 792,084 9.12 143,692 $ 23.62 $23.68 - $23.68 130,000 9.16 0 $ — $24.71 - $24.71 33,225 9.39 0 $ — 4,838,598 7.69 2,074,120 $ 8.25
Schedule of Estimated Grant Date Fair Value of Employee Stock Options	The estimated grant date fair value of employee stock options with time-based vesting terms was calculated using the Black-Scholes valuation model, based on the following assumptions: Year Ended December 31, 2017 2016 2015 Expected term 5.0 – 6.0 years 5.3 – 6.0 years 5.4 – 6.0 years Expected volatility 78 - 81% 67 – 74% 65 – 75% Risk-free interest rate 1.7 – 2.3% 1.1 – 1.9% 1.5 – 1.9% Expected dividend yield —% —% —%
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	A summary of RSU activity is as follows: RSU Awards Outstanding Number of Shares Weighted-Average Grant Date Fair Market Value Aggregate Intrinsic Value (in thousands) 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 RSUs granted 380,500 $ 4.01 RSUs released (89,722 ) $ 8.22 RSUs cancelled (57,750 ) $ 6.71 Balance, December 31, 2016 605,052 $ 5.60 $ 7,878 RSUs granted 544,185 $ 20.61 RSUs released (185,889 ) $ 6.24 RSUs cancelled (72,116 ) $ 9.22 Balance, December 31, 2017 891,232 $ 14.34 $ 9,572
Black Scholes
Schedule of Estimated Grant Date Fair Value of Employee Stock Options	The fair value of options granted to non-employees during the years ended December 31, 2017 and 2016 was estimated using Black-Scholes with the following assumptions: Year Ended December 31, 2017 2016 Expected term 0.25 – 9.39 years 0.8 – 1.0 years Expected volatility 48 - 80% 63 – 125% Risk-free interest rate 0.9 – 2.4% 0.6 – 0.9% Expected dividend yield —% —%
Monte Carlo Simulation
Schedule of Estimated Grant Date Fair Value of Employee Stock Options	The fair value of awards granted to non-employees was estimated using Monte-Carlo with the following assumptions: Year Ended December 31, 2017 2016 Expected term 0.5–3.5 years 2.2–6.0 years Expected volatility 75-80% 70% Risk-free interest rate 2.1–2.4% 1.4%–2.3% Expected dividend yield —% —%

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
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, 2017, 2016 and 2015 is as follows: Year Ended December 31, 2017 2016 2015 Statutory tax rate 34.00 % 34.00 % 34.00 % State taxes, net of federal benefits 1.38 % 0.96 % -3.62 % Stock-based compensation -0.16 % -0.62 % -1.20 % Credits 1.99 % 1.46 % 3.30 % Other -0.64 % -0.10 % -0.54 % Valuation allowance -4.03 % -26.22 % -31.94 % Warrant valuation 0.00 % -9.48 % 0.00 % Tax rate change -32.54 % 0.00 % 0.00 % Effective tax rate 0.00 % 0.00 % 0.00 %
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences and carryforwards that give rise to the Company’s deferred tax assets are as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss carry forwards $ 68,807 $ 71,858 Research and development credit 17,365 10,969 Intangible assets 824 1,653 Depreciation — 191 Temporary differences 8,017 4,682 Gross Deferred tax assets 95,013 89,353 Less: valuation allowance (95,013 ) (89,353 ) 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, 2017 2016 2015 Balance at beginning of year $ 1,197 $ 957 $ — Increase related to current year tax provision 516 240 162 Increase related to tax rate change 144 — — Increase related to prior year tax provision — — 795 Balance at end of year $ 1,857 $ 1,197 $ 957

Selected Unaudited Quarterly 33

Selected Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2017
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 2017 and 2016 (in thousands, except per share amounts): Three Months Ended December 31, 2017 September 30, 2017 June 30, 2017 March 31, 2017 Contract revenue 1,869 577 1,266 7,463 Operating expenses 43,973 37,121 31,059 25,348 Other income (expense), net 5,722 6,637 3,723 (15,374 ) Net loss (36,382 ) (29,907 ) (26,070 ) (33,259 ) Net loss per common share: Basic (0.86 ) (0.71 ) (0.68 ) (0.93 ) Diluted (0.98 ) (0.85 ) (0.78 ) (0.93 ) Weighted-average shares used to calculate net loss per common share: Basic 42,422,592 42,259,001 38,072,763 35,725,876 Diluted 43,257,602 43,211,059 39,092,279 35,725,876 Three Months Ended December 31, 2016 September 30, 2016 June 30, 2016 March 31, 2016 Contract revenue 10,734 16,046 9,144 5,849 Operating expenses 22,796 24,996 25,659 17,670 Other income (expense), net (17,662 ) (2,088 ) (1,753 ) (376 ) Net loss (29,724 ) (11,038 ) (18,268 ) (12,197 ) Net loss per common share: Basic (1.04 ) (0.41 ) (0.87 ) (0.66 ) Diluted (1.04 ) (0.41 ) (0.87 ) (0.66 ) Weighted-average shares used to calculate net loss per common share: Basic 28,653,045 26,789,397 20,899,297 18,398,288 Diluted 28,653,045 26,789,397 20,899,297 18,398,288 (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 Pre34

Organization and Basis of Presentation and Consolidation - Additional Information (Details) - USD ($)

Feb. 27, 2018

Jun. 09, 2017

May 31, 2017

May 04, 2017

Dec. 19, 2016

Jun. 03, 2016

Sep. 30, 2017

May 31, 2017

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Apr. 07, 2015

Subsidiary, Sale of Stock [Line Items]

Value authorized of equity instruments to be issued

$ 150,000,000

Proceeds from offering net of underwriting discounts and commissions and offering expenses

$ 3,827,000

$ 1,319,000

Warrants to purchase common stock, exercise price

$ 3.78

Effective agreement terms

The Global Access Commitments will continue in effect until the earlier of 25 years from the closing of the Gates Investment or 7 years following the termination of all funding provided by the Gates Foundation; provided, that the Global Access Commitments will continue for any products or services developed with funding provided by the Gates Foundation which continue to be developed or available in certain developing countries.

Research and development contract

$ 12,000,000

Cash, cash equivalents and short-term investments

$ 164,800,000

Accumulated deficit

$ 372,838,000

$ 247,220,000

Subsequent Event

Subsidiary, Sale of Stock [Line Items]

Research and development contract

$ 18,000,000

Bill & Melinda Gates Foundation

Subsidiary, Sale of Stock [Line Items]

Research and development awarded grant funding

$ 13,200,000

Research term

3 years

3 years

Advance amount received for research and development

$ 3,200,000

$ 3,200,000

$ 3,200,000

Private Placement

Subsidiary, Sale of Stock [Line Items]

Proceeds from issuance or sale of equity

$ 25,400,000

Aggregate net proceeds from issuance of common stock

$ 25,100,000

Warrants to purchase common stock, exercise price

$ 3.66

Weighted average contractual term

5 years

Private Placement | Bill & Melinda Gates Foundation

Subsidiary, Sale of Stock [Line Items]

Share price (dollars per share)

$ 24.55

Proceeds from issuance or sale of equity

$ 10,000,000

Underwritten Public Offering

Subsidiary, Sale of Stock [Line Items]

Shares issued

5,750,000

7,475,000

5,750,000

Share price (dollars per share)

$ 22.50

$ 13.50

$ 22.50

Proceeds from offering net of underwriting discounts and commissions and offering expenses

$ 121,200,000

$ 94,600,000

$ 121,200,000

Additional shares of common stock

750,000

975,000

Maximum

Subsidiary, Sale of Stock [Line Items]

Research and development awarded grant funding

$ 18,000,000

Maximum | Bill & Melinda Gates Foundation

Subsidiary, Sale of Stock [Line Items]

Research and development awarded grant funding

$ 10,500,000

$ 10,500,000

Maximum | Private Placement

Subsidiary, Sale of Stock [Line Items]

Weighted average contractual term

5 years

ATM equity offering program

Subsidiary, Sale of Stock [Line Items]

Value authorized of equity instruments to be issued

$ 30,000,000

Shares issued

1,105,549

Proceeds from issuance of common stock, gross of issuance costs

$ 5,300,000

Proceeds from offering net of underwriting discounts and commissions and offering expenses

$ 5,100,000

ATM equity offering program | Weighted Average

Subsidiary, Sale of Stock [Line Items]

Share price (dollars per share)

$ 4.82

Common Stock

Subsidiary, Sale of Stock [Line Items]

Shares issued

907,711

197,838

Common Stock | Private Placement

Subsidiary, Sale of Stock [Line Items]

Shares issued

7,999,996

7,999,996

Number of shares authorized to be purchased

1,999,999

Redeemable Common Stock | Private Placement | Bill & Melinda Gates Foundation

Subsidiary, Sale of Stock [Line Items]

Shares issued

407,331

Summary of Significant Accoun35

Summary of Significant Accounting Policies - Additional Information (Details)	May 04, 2017USD ($)$ / shares	Jun. 03, 2016$ / sharesshares	Sep. 30, 2017USD ($)	May 31, 2017USD ($)$ / sharesshares	Dec. 31, 2017USD ($)Segment$ / sharesshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014shares
Summary of Significant Accounting Policies [Line Items]
Restricted cash					$ 9,700,000	$ 400,000
Restricted cash, current					$ 5,891,000	127,000
Facility lease expiration term					90 days
Number of operating segments | Segment					1
Allowance for doubtful accounts receivable					$ 0	$ 0
Warrants to purchase common stock, exercise price | $ / shares					$ 3.78
Warrants to purchase common stock outstanding and unexercised | shares					1,196,296
Common stock, shares outstanding | shares					42,515,015	35,638,052
Private Placement
Summary of Significant Accounting Policies [Line Items]
Warrants to purchase common stock, exercise price | $ / shares		$ 3.66
Weighted average contractual term		5 years
Common Stock
Summary of Significant Accounting Policies [Line Items]
Common stock, shares outstanding | shares					42,107,684	35,638,052	18,395,219	17,907,135
Common Stock | Private Placement
Summary of Significant Accounting Policies [Line Items]
Number of shares authorized to be purchased | shares		1,999,999
Warrants to purchase common stock outstanding and unexercised | shares					1,178,782
Impairment of Asset
Summary of Significant Accounting Policies [Line Items]
Impairment charges					$ 0	$ 0	$ 0
Minimum
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life					3 years
Maximum
Summary of Significant Accounting Policies [Line Items]
Research and development awarded grant funding			$ 18,000,000
Property, plant and equipment, useful life					7 years
Maximum | Private Placement
Summary of Significant Accounting Policies [Line Items]
Weighted average contractual term		5 years
Facility Leases
Summary of Significant Accounting Policies [Line Items]
Restricted cash, current					$ 500,000	400,000
Bill & Melinda Gates Foundation
Summary of Significant Accounting Policies [Line Items]
Restricted cash, current					$ 9,200,000	$ 0
Research and development awarded grant funding				$ 13,200,000
Bill & Melinda Gates Foundation | Private Placement
Summary of Significant Accounting Policies [Line Items]
Share price (dollars per share) | $ / shares	$ 24.55
Bill & Melinda Gates Foundation | Contingently Redeemable Common Stock
Summary of Significant Accounting Policies [Line Items]
Shares issued | shares				407,331
Share price (dollars per share) | $ / shares				$ 24.55
Bill & Melinda Gates Foundation | Contingently Redeemable Common Stock | Mezzanine Equity
Summary of Significant Accounting Policies [Line Items]
Common stock, shares outstanding | shares					407,331
Bill & Melinda Gates Foundation | Maximum
Summary of Significant Accounting Policies [Line Items]
Research and development awarded grant funding	$ 10,500,000			$ 10,500,000

Summary of Significant Accoun36

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash and cash equivalents	$ 145,219	$ 118,964	$ 20,287
Restricted cash, current	5,891	127
Restricted cash, non-current	3,855	250	127
Total cash, cash equivalents, and restricted cash	$ 154,965	$ 119,341	$ 20,414	$ 19,008

Summary of Significant Accoun37

Summary of Significant Accounting Policies - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net loss	$ (36,382)	$ (29,907)	$ (26,070)	$ (33,259)	$ (29,724)	$ (11,038)	$ (18,268)	$ (12,197)	$ (125,618)	$ (71,227)	$ (27,093)
Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share									39,645,635	23,707,063	18,147,986
Basic and diluted net loss per common share									$ (3.17)	$ (3)	$ (1.49)
Accumulated Deficit
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net loss									$ (125,618)	$ (71,227)	$ (27,093)

Summary of Significant Accoun38

Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Outstanding Excluded from the Computations of Diluted Weighted-Average Shares Outstanding (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding (shares)	4,838,598	3,540,293	2,387,337
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding (shares)	891,232	605,052	372,024
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding (shares)	1,196,296	1,322,754	30,024

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Liabilities Measured and Recognized at Fair Value (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 174,537	$ 146,260
Unrealized Losses		(7)
Fair Value	174,537	146,253
Short-term investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	19,572	26,912
Restricted cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	9,746	377
Cash and cash equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	145,219	118,964
Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost		3,728
Fair Value		3,728
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	73,507	115,613
Fair Value	73,507	115,613
Level 1 | US Treasury bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	4,992
Fair Value	4,992
Level 1 | Restricted cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	9,746	377
Fair Value	9,746	377
Level 1 | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	58,769	115,236
Fair Value	58,769	115,236
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	101,030	26,919
Unrealized Losses		(7)
Fair Value	101,030	26,912
Level 2 | U.S. agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	4,990
Fair Value	4,990
Level 2 | Other debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	50,000
Fair Value	50,000
Level 2 | Commercial paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	46,040	13,950
Fair Value	46,040	13,950
Level 2 | Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost		12,969
Unrealized Losses		(7)
Fair Value		12,962
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrant Liability	9,774	13,874
Derivative Liability	686	602
Total	$ 10,460	$ 14,476

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	Jun. 03, 2016	Aug. 05, 2015	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Sale of available-for-sale securities				$ 0	$ 0
Change in estimated fair value				(1,928,000)	19,859,000	$ 19,000
Potential payment to solar capital				$ 1,000,000
Discount rate, percent				13.00%
Decrease in discount rate percent effecting fair value of derivative liability				5.00%
Warrants to purchase common stock, exercise price				$ 3.78
Issuance of derivative in connection with issuance of loan payable						$ 356,000
Warrant liability			$ 13,874,000	$ 9,774,000	13,874,000
Exercise of warrants to purchase common stock			707,269
Proceeds from exercise of stock warrants			$ 1,200,000	$ 418,000	1,151,000
Estimated fair value of warrants exercised	$ 900,000		8,300,000		$ 8,300,000
Increase in estimated fair value of warrants exercised			7,400,000
Dividend yield				0.00%	0.00%
Change in percent effecting fair value of derivative liability					5.00%
Effect in fair value of derivative liability due to change in percent of FDA approval probability			593,000		$ 593,000
Private Placement
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants to purchase common stock, exercise price	$ 3.66
Common Stock | Private Placement
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants to purchase common stock	1,999,999
Derivative Financial Instruments, Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Effect in fair value of derivative liability due to decrease in discount rate percent				$ 59,000
Level 3 | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative liability			602,000	686,000	602,000
Warrant liability			13,900,000	9,800,000	13,900,000
Derivative | Level 3 | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in estimated fair value				84,000	227,000
Derivative liability				686,000
Warrants to purchase common stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Proceeds from exercise of stock warrants				400,000
Estimated fair value of warrants exercised			$ 1,200,000	2,100,000	1,200,000
Increase in estimated fair value of warrants exercised				$ 900,000
Warrants to purchase common stock | Common Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Exercise of warrants to purchase common stock				113,948
Warrants to purchase common stock | Level 3 | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in estimated fair value				$ (2,012,000)	19,632,000
Issuance of derivative in connection with issuance of loan payable	$ 2,600,000				$ 2,579,000
Secured Debt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Success fee		$ 1,000,000
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized loss position				$ 0

Fair Value Measurements - Assum

Fair Value Measurements - Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Expected volatility	80.00%
Dividend yield	0.00%	0.00%
Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Expected volatility		60.00%
Expected term	3 years 4 months 24 days	4 years 4 months 24 days
Risk-free interest rate	1.60%	1.00%
Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Expected volatility		80.00%
Expected term	4 years 3 months 18 days	5 years
Risk-free interest rate	2.00%	1.90%

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Estimated Fair Value of Liabilities Measurements (Details) - USD ($)	Jun. 03, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Estimated fair value of derivative liability and warrants issued				$ 356,000
Change in estimated fair value		$ (1,928,000)	$ 19,859,000	19,000
Level 3 | Estimated Fair Value of Derivative Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Estimated Fair Value, Beginning Balance			375,000
Estimated fair value of derivative liability and warrants issued				356,000
Change in estimated fair value				19,000
Estimated Fair Value, Ending Balance				375,000
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Estimated Fair Value, Beginning Balance		14,476,000
Estimated Fair Value, Ending Balance		10,460,000	14,476,000
Level 3 | Fair Value, Measurements, Recurring | Derivative
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Estimated Fair Value, Beginning Balance		602,000	375,000
Change in estimated fair value		84,000	227,000
Estimated Fair Value, Ending Balance		686,000	602,000	375,000
Level 3 | Fair Value, Measurements, Recurring | Warrants to purchase common stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Estimated Fair Value, Beginning Balance		13,874,000
Estimated fair value of derivative liability and warrants issued	$ 2,600,000		2,579,000
Change in estimated fair value		(2,012,000)	19,632,000
Reclassification of warrant liability to additional paid -in -capital upon exercise of warrants		(2,088,000)	(8,337,000)
Estimated Fair Value, Ending Balance		$ 9,774,000	$ 13,874,000

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Prepaids and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expense And Other Assets Current [Abstract]
Deferred research and development costs	$ 4,317	$ 660
Prepaid expenses	1,755	1,390
Other current assets	295	139
Prepaids and other current assets	$ 6,367	$ 2,189

Balance Sheet Components - Sc44

Balance Sheet Components - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 17,921	$ 7,650
Less: accumulated depreciation	(3,111)	(4,389)
Property and equipment, net	14,810	3,261
Office equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	863	644
Laboratory equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	6,663	4,038
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	9,355	1,072
Property and equipment, net	6,600
Construction-in-progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,040	$ 1,896

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Depreciation expense	$ 1.3	$ 0.4	$ 0.4

Balance Sheet Components - Sc46

Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued clinical and development expenses	$ 6,480	$ 3,681
Payroll and related bonus expenses	6,281	4,941
Other	2,680	1,076
Accrued liabilities	$ 15,441	$ 9,698

License and Collaboration Agr47

License and Collaboration Agreements - Additional Information (Details)	1 Months Ended			12 Months Ended
	Nov. 30, 2017USD ($)	May 31, 2016USD ($)	Jan. 31, 2006USD ($)$ / sharesshares	Dec. 31, 2017USD ($)milestone	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense				$ 95,598,000	$ 73,999,000	$ 40,228,000
Thermo Fisher Scientific, Inc
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments for first commercialization product	$ 6,800,000
Research and development expense				2,500,000	1,200,000	0
Crystal Biosciences, Inc
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments for first commercialization product		$ 20,600,000
Ionis Pharmaceuticals License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments for first commercialization product			$ 19,500,000
Research and development expense				0	$ 0	$ 0
Milestone payments for second commercialization product			9,800,000
Aggregate additional milestone payments			20,000,000
Cumulative milestones compensation				$ 7,000,000
Number of milestones paid in relation to license agreement | milestone				3
Ionis Pharmaceuticals License Agreement | Up-front License Fee
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense			$ 1,500,000
Ionis Pharmaceuticals License Agreement | Up-front License Fee | Series A Convertible Preferred Stock
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Shares issued | shares			97,402
Shares issued price per share (dollars per share) | $ / shares			$ 15.40

Revenue Contracts - Additional

Revenue Contracts - Additional Information (Details) - USD ($)	May 04, 2017	Sep. 30, 2017	Jun. 30, 2017	May 31, 2017	Apr. 30, 2017	May 26, 2016	Apr. 30, 2016	Jan. 31, 2016	Jul. 31, 2015	Apr. 30, 2013	Sep. 30, 2012	Aug. 31, 2010	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development contract		$ 12,000,000
Biomedical Advanced Research and Development Authority
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Contracts revenue														$ 7,700,000	$ 39,500,000	$ 17,600,000
Research and development contract					$ 124,300,000					$ 103,800,000	$ 43,400,000	$ 27,600,000
Term of agreement, in years												2 years
Increase in research and development contract					500,000	$ 20,000,000				$ 60,400,000	$ 15,800,000
Research and development contract remaining available funding													$ 124,300,000
Contracts receivable													0	0	11,700,000
C-Scape Contract
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Contracts revenue														1,000,000
Research and development contract		12,000,000
Research and development contract remaining available funding														11,000,000
Contracts receivable													1,000,000	1,000,000
DTRA
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Contracts revenue																7,122,000
National Institute of Allergy and Infectious Diseases
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Contracts revenue														1,300,000	2,300,000	$ 1,400,000
Research and development contract			$ 5,300,000		4,700,000		$ 4,400,000		$ 1,500,000
Increase in research and development contract			600,000		$ 300,000			$ 500,000
Research and development contract remaining available funding			$ 400,000
Contracts receivable													$ 200,000	200,000	500,000
Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development awarded grant funding		18,000,000
Maximum | C-Scape Contract
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development awarded grant funding		$ 18,000,000
Bill & Melinda Gates Foundation
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development awarded grant funding				$ 13,200,000
Research term	3 years			3 years
Advance amount received for research and development	$ 3,200,000			$ 3,200,000
Contracts revenue														$ 1,100,000	$ 0
Bill & Melinda Gates Foundation | Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development awarded grant funding	$ 10,500,000			$ 10,500,000

Commitments - Facilities Lease

Commitments - Facilities Lease Obligation (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2016USD ($)ft²	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Aug. 31, 2017ft²	Aug. 17, 2017USD ($)	Jul. 31, 2017USD ($)ft²
Operating Leased Assets [Line Items]
Square feet of office, laboratory and research and development space (sq feet) | ft²							98,984
Lease extended term date		Jan. 31, 2028
Expansion option (in years)		5 years
Lessor Leasing Arrangements, Operating Leases, Rental Increase, Percent	3.50%
One time improvement allowance	$ 5,700	$ 1,000
Additional allowance	$ 900	1,500
Aggregate Increase in base rent						$ 1,700
Property and equipment, net		$ 14,810	$ 3,261
Period available to pay balance of Original Additional Allowance and Expansion Additional Allowance		36 months
Rent expense		$ 3,000	$ 600	$ 500
Leasehold improvements
Operating Leased Assets [Line Items]
Property and equipment, net		$ 6,600
Original Space
Operating Leased Assets [Line Items]
Square feet of office, laboratory and research and development space (sq feet) | ft²	47,118
First year base rent	$ 2,900
One time, first year rent abatement	$ 1,800
Expansion Space
Operating Leased Assets [Line Items]
Square feet of office, laboratory and research and development space (sq feet) | ft²							51,866
Expected operating lease area of real estate property | ft²					18,888
One time, first year rent abatement							$ 2,000

Commitments - Schedule of Futur

Commitments - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Year Ending December 31,
2,018	$ 4,028
2,019	6,201
2,020	6,418
2,021	6,645
2,022	6,877
Thereafter	38,780
Total minimum lease payments	$ 68,949

Commitments - Commercial Valida

Commitments - Commercial Validation and Manufacturing Agreement (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Mar. 31, 2017	Jul. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Prepaid and other current assets			$ 6,367	$ 2,189
Research and development			95,598	73,999	$ 40,228
Hovione Limited
Loss Contingencies [Line Items]
Commercial manufacturing agreement initial term	7 years
Percentage of long term purchase commitment minimum required quantity	80.00%
Number of years for minimum supply percentage after approval	3 years
Minimum annual purchase commitments beginning year	2,020
Annual purchase commitments ending Year	2,024
Advance payments		$ 1,500	6,200
Prepaid and other current assets			4,300	700
Commitment under Cancellation Clause			9,500
Aggregate amount of potential commitments			23,700
Research and development			$ 3,300	$ 1,200	$ 0
Hovione Limited | Minimum
Loss Contingencies [Line Items]
Percentage of long term purchase commitment	40.00%
Hovione Limited | Maximum
Loss Contingencies [Line Items]
Percentage of long term purchase commitment	66.00%

Commitments - Gaurantees and In

Commitments - Gaurantees and Indemnifications (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Liabilities	$ 65,109,000	$ 57,190,000
Indemnification Rights and Agreements
Loss Contingencies [Line Items]
Liabilities	$ 0	$ 0

Borrowings - Additional Informa

Borrowings - Additional Information (Details) - USD ($)	Jun. 20, 2016	Aug. 05, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Face amount			$ 20,833,000
Proceeds from issuance of loan payable				$ 10,000,000	$ 14,590,000
Final fee due at maturity in 2019			2,000,000
Interest expense			2,855,000	2,320,000	699,000
Secured Debt
Debt Instrument [Line Items]
Debt, maturity date		Aug. 5, 2019
Proceeds from issuance of loan payable	$ 10,000,000	$ 15,000,000
Interest rate per annum (percent)		6.99%
Variable interest rate (percent)		1.00%
Repayment of debt term (months)		24 months
Increase in interest rate in event of default (percent)		4.00%
Closing fee		$ 250,000
Final fee (percent)		8.00%
Success fee		$ 1,000,000
Fair value of success fee		356,000
Final fee due at maturity in 2019		2,000,000
Interest expense			$ 2,900,000	$ 2,300,000	$ 700,000
Secured Debt | Maximum
Debt Instrument [Line Items]
Face amount		$ 25,000,000

Borrowings - Future Minimum Deb

Borrowings - Future Minimum Debt Obligation Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
2,018	$ 12,500
2,019	8,333
Total principal payments	20,833
Final fee due at maturity in 2019	2,000
Total principal and final fee payments	22,833
Unamortized discount and debt issuance costs	(876)
Total loan obligation	21,957
Less current portion	(12,500)	$ (4,167)
Loan payable, long-term	$ 9,457	$ 21,110

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	Jun. 09, 2017	May 31, 2017	Dec. 19, 2016	Jun. 03, 2016	May 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 07, 2015	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value authorized of equity instruments to be issued									$ 150,000,000
Proceeds from offering net of underwriting discounts and commissions and offering expenses							$ 3,827,000	$ 1,319,000
Warrants to purchase common stock, exercise price						$ 3.78
Estimated fair values of the common stock and warrants issued							3,827,000	1,319,000
Issuance of derivative in connection with issuance of loan payable								$ 356,000
Warrants to purchase common stock | Level 3 | Fair Value, Measurements, Recurring
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of derivative in connection with issuance of loan payable				$ 2,600,000			2,579,000
Notes Payable to Banks | Oxford Finance LLC and SVB | Series C Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized to be purchased										20,016	10,008
Warrants to purchase common stock, exercise price										$ 11.99
Fair value of warrants										$ 163,000	$ 86,000
Notes Payable to Banks | Silicon Valley Bank | Series C Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized to be purchased										5,896
Warrant To Purchase Shares Of Common Exercised										12,510
Underwritten Public Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued		5,750,000	7,475,000		5,750,000
Share price (dollars per share)		$ 22.50	$ 13.50		$ 22.50
Additional shares of common stock	750,000		975,000
Proceeds from offering net of underwriting discounts and commissions and offering expenses		$ 121,200,000	$ 94,600,000		$ 121,200,000
Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants to purchase common stock, exercise price				$ 3.66
Proceeds from issuance or sale of equity				$ 25,400,000
Weighted average contractual term				5 years
Estimated fair values of the common stock and warrants issued							$ 22,587,000
Private Placement | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued				141,453
Number of shares authorized to be purchased				35,363
Proceeds from issuance or sale of equity				$ 500,000
Payments of stock issuance costs				$ 300,000
Maximum | Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average contractual term				5 years
ATM equity offering program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value authorized of equity instruments to be issued									30,000,000
Shares issued						1,105,549
Proceeds from issuance of common stock, gross of issuance costs						$ 5,300,000
Proceeds from sale of stock, net of commissions and other transaction costs						5,100,000
Value of common stock remaining available to be sold						24,700,000
Proceeds from offering net of underwriting discounts and commissions and offering expenses						$ 5,100,000
ATM equity offering program | Weighted Average
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share price (dollars per share)						$ 4.82
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued							907,711	197,838
Estimated fair values of the common stock and warrants issued							$ 1,000
Common Stock | Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued				7,999,996			7,999,996
Number of shares authorized to be purchased				1,999,999
Estimated fair values of the common stock and warrants issued				$ 22,900,000			$ 8,000
Cowen and Company, LLC | ATM equity offering program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value authorized of equity instruments to be issued									$ 30,000,000

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Warrants to Purchase Shares of Common Stock (Details)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Class of Warrant or Right [Line Items]
Shares | shares	1,196,296
Exercise Price | $ / shares	$ 3.78
April 30, 2012 Warrants | Oxford Finance LLC
Class of Warrant or Right [Line Items]
Shares | shares	11,676
Exercise Price | $ / shares	$ 11.99
Expiration Date	Nov. 1, 2021
November 1, 2011 Warrants | Oxford Finance LLC
Class of Warrant or Right [Line Items]
Shares | shares	5,838
Exercise Price | $ / shares	$ 11.99
Expiration Date	Nov. 1, 2021
June 3, 2016 Warrants | Growth Equity Opportunities Fund IV, LLC
Class of Warrant or Right [Line Items]
Shares | shares	1,178,782
Exercise Price | $ / shares	$ 3.66
Expiration Date	Jun. 3, 2021

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 13, 2017	Jan. 02, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized			2,325,522	1,235,808	716,285
Outstanding shares available for future issuance (shares)			967,078	639,374	893,462	1,111,470
Shares subject to options outstanding (shares)			4,838,598	3,540,293	2,387,337	1,885,372
Stock-based compensation expense			$ 13,652	$ 3,847	$ 2,983
Options granted (shares)			1,806,157	1,477,600	929,100
Options granted, weighted average grant date fair value (in dollars per share)			$ 21.12	$ 4.10	$ 5.02
Unrecognized stock-based compensation			$ 22,200
Weighted-average period of cost expected to be recognized			2 years 11 months 12 days
Non-Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 500	$ 100
Stock Options and Restricted Stock Units | Former Chief Medical Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 700
Equity Option | Non-Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (shares)			3,000	15,000	0
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted			544,185	380,500	291,525
Weighted-average grant date fair market value, shares granted (dollars per share)			$ 20.61	$ 4.01	$ 7.76
Restricted stock units | Non-Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted			1,500	0	0
Restricted stock units | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Weighted-average period of cost expected to be recognized			2 years 8 months 26 days
Shares granted			544,185	380,500	291,525
Weighted-average grant date fair market value, shares granted (dollars per share)			$ 20.61	$ 4.01	$ 7.76
Unrecognized compensation costs			$ 11,000
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized		178,190
Outstanding shares available for future issuance (shares)			274,951
Common stock issued (shares)			411,716
2014 Equity Incentive Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized		1,425,522
Outstanding shares available for future issuance (shares)			850,639
Vesting period			4 years
Option expiration period			10 years
2014 Employment Commencement Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized	450,000
Outstanding shares available for future issuance (shares)			116,439
Number of shares authorized (shares)			2,050,000
Stock Incentive Plan 2003
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Option expiration period			10 years
Shares subject to options outstanding (shares)			829,586
Employees That Contain Performance Conditions | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted			35,050	59,925	0
Employees That Contain Performance Conditions | Options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (shares)			184,200	354,250	0

Equity Incentive Plans - Schedu

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 13,652	$ 3,847	$ 2,983
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	6,340	2,165	1,404
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 7,312	$ 1,682	$ 1,579

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options granted
Outstanding options, aggregate intrinsic value	$ 14,174	$ 23,837	$ 293
Options exercised, aggregate intrinsic value		89	923
Options vested and exercisable, aggregate intrinsic value	7,705
Options vested and expected to vest, aggregate intrinsic value	$ 14,005
Options exercised, aggregate intrinsic value		$ 89	$ 923
Shares Available for grant
Beginning balance (shares)	639,374	893,462	1,111,470
Additional shares reserved (shares)	2,325,522	1,235,808	716,285
Options granted (shares)	(1,806,157)	(1,477,600)	(929,100)
Options exercised (shares)	0	0	0
Options forfeited (shares)	280,408	310,454	237,007
Ending balance (shares)	967,078	639,374	893,462
Weighted-Average Remaining Contractual Life (in years)
Options vested and exercisable, weighted-average remaining contractual life (in years)	6 years 4 months 28 days
Options vested and expected to vest, weighted-average remaining contractual life (in years)	7 years 8 months 12 days
Weighted- Average Remaining Contractual Term (years)	7 years 8 months 8 days	7 years 11 months 23 days
Number of Shares
Beginning balance (shares)	3,540,293	2,387,337	1,885,372
Additional shares reserved (shares)	0	0	0
Options granted (shares)	1,806,157	1,477,600	929,100
Options exercised (shares)	(227,444)	(14,190)	(190,128)
Options forfeited (shares)	(280,408)	(310,454)	(237,007)
Ending balance (shares)	4,838,598	3,540,293	2,387,337
Vested and exercisable	2,074,120
Vested and expected to vest	4,704,835
Weighted- Average Exercise Price
Beginning balance (shares)	$ 6.31	$ 7.92	$ 7.95
Options granted (shares)	21.12	4.10	7.95
Options exercised (shares)	7.23	4.59	5.54
Options forfeited (shares)	9.14	8.19	10.22
Ending balance (shares)	11.63	$ 6.31	$ 7.92
Vested and exercisable	8.25
Vested and expected to vest	$ 11.50
Restricted stock units
Shares Available for grant
Shares granted	(544,185)	(380,500)	(291,525)
Shares cancelled	72,116	57,750	49,325
Shares cancelled	72,116	57,750	49,325

Equity Incentive Plans - Summ60

Equity Incentive Plans - Summary of Stock Options Outstanding by Exercise Price Range (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number of Options (in shares)	4,838,598	3,540,293	2,387,337	1,885,372
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	7 years 8 months 8 days	7 years 11 months 23 days
Vested and Exercisable, Number of Options (in shares)	2,074,120
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 8.25
$3.41 - $3.68
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	3.41
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 3.68
Options Outstanding, Number of Options (in shares)	502,764
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	7 years 10 months 2 days
Vested and Exercisable, Number of Options (in shares)	213,306
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 3.65
$3.65 - $4.44
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	3.65
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 4.44
Options Outstanding, Number of Options (in shares)	594,704
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	8 years 7 months 9 days
Vested and Exercisable, Number of Options (in shares)	211,184
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 4.28
$4.62 - $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	4.62
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 5.86
Options Outstanding, Number of Options (in shares)	608,616
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	7 years 2 months 26 days
Vested and Exercisable, Number of Options (in shares)	404,603
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 5.18
$6.60 - $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	6.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 7.26
Options Outstanding, Number of Options (in shares)	722,468
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	4 years 10 months 20 days
Vested and Exercisable, Number of Options (in shares)	534,692
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 7.03
$8.04 - $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	8.04
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 10.44
Options Outstanding, Number of Options (in shares)	508,994
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	6 years 2 months 8 days
Vested and Exercisable, Number of Options (in shares)	379,275
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 9.17
$10.98 - $16.18
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	10.98
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 16.18
Options Outstanding, Number of Options (in shares)	528,793
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	8 years 5 months 8 days
Vested and Exercisable, Number of Options (in shares)	148,841
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 12.41
$17.55 - $22.93
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	17.55
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 22.93
Options Outstanding, Number of Options (in shares)	416,950
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	9 years 5 months 1 day
Vested and Exercisable, Number of Options (in shares)	38,527
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 22.08
$23.62 - $23.62
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	23.62
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 23.62
Options Outstanding, Number of Options (in shares)	792,084
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	9 years 1 month 13 days
Vested and Exercisable, Number of Options (in shares)	143,692
Vested and Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 23.62
$23.68 - $23.68
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	23.68
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 23.68
Options Outstanding, Number of Options (in shares)	130,000
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	9 years 1 month 28 days
Vested and Exercisable, Number of Options (in shares)	0
$24.71 - $24.71
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	$ 24.71
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit	$ 24.71
Options Outstanding, Number of Options (in shares)	33,225
Options Outstanding, Weighted-Average Remaining Contractual Life (in Years)	9 years 4 months 20 days
Vested and Exercisable, Number of Options (in shares)	0

Equity Incentive Plans - Sche61

Equity Incentive Plans - Schedule of Estimated Grant Date Fair Value of Employee Stock Options Using Black-Scholes Valuation Model (Detail) - Options to purchase common stock	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Expected volatility, minimum	78.00%	67.00%	65.00%
Expected volatility, maximum	81.00%	74.00%	75.00%
Risk-free interest rate, minimum	1.70%	1.10%	1.50%
Risk-free interest rate, maximum	2.30%	1.90%	1.90%
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	5 years 3 months 18 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	6 years	6 years	6 years

Equity Incentive Plans - Sche62

Equity Incentive Plans - Schedule of Estimated Grant Date Fair Value of Employee Stock Options (Details) - Black Scholes - Non-Employee	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Expected volatility, minimum	48.00%	63.00%
Expected volatility, maximum	80.00%	125.00%
Risk-free interest rate, minimum	0.90%	0.60%
Risk-free interest rate, maximum	2.40%	0.90%
Expected dividend yield	0.00%	0.00%
Minimum
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Expected term	3 months	9 months 18 days
Maximum
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Expected term	9 years 4 months 20 days	1 year

Equity Incentive Plans - Summ63

Equity Incentive Plans - Summary of Restricted Stock Activity (Details) - Restricted stock units - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Shares
Beginning balance (shares)	605,052	372,024	168,200
Shares granted	544,185	380,500	291,525
Shares released	(185,889)	(89,722)	(38,376)
Shares cancelled	(72,116)	(57,750)	(49,325)
Ending balance (shares)	891,232	605,052	372,024
Weighted-Average Grant Date Fair Market Value
Beginning balance (dollars per share)	$ 5.60	$ 8.02	$ 9.33
Weighted-average grant date fair market value, shares granted (dollars per share)	20.61	4.01	7.76
Shares released (dollars per share)	6.24	8.22	9.42
Shares canceled (dollars per share)	9.22	6.71	9.80
Ending balance (dollars per share)	$ 14.34	$ 5.60	$ 8.02
Aggregate Intrinsic Value (in thousands)
RSU Awards Outstanding, aggregate intrinsic value	$ 9,572	$ 7,878	$ 2,135	$ 2,195

Equity Incentive Plans - Sche64

Equity Incentive Plans - Schedule of Estimated Fair Value of Awards Granted to Employees using Monte-Carlo Assumptions (Details) - Monte Carlo Simulation	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Expected volatility, minimum	75.00%
Expected volatility, maximum	80.00%
Expected volatility		70.00%
Risk-free interest rate, minimum	2.10%	1.40%
Risk-free interest rate, maximum	2.40%	2.30%
Expected dividend yield	0.00%	0.00%
Minimum
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Expected term	6 months	2 years 2 months 12 days
Maximum
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Expected term	3 years 6 months	6 years

Contingently Redeemable Commo65

Contingently Redeemable Common Stock - Additional Information (Details) - Contingently Redeemable Common Stock $ / shares in Units, $ in Millions	1 Months Ended
	May 31, 2017USD ($)$ / sharesshares
Temporary Equity [Line Items]
Percentage of purchase price compounded annual interest	5.00%
Mezzanine Equity
Temporary Equity [Line Items]
Proceeds from issuance or sale of equity | $	$ 10
Shares issued | shares	407,331
Bill & Melinda Gates Foundation
Temporary Equity [Line Items]
Shares issued | shares	407,331
Share price (dollars per share) | $ / shares	$ 24.55
Proceeds from issuance or sale of equity | $	$ 10

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of the Statutory Tax Rates and the Effective Tax Rates (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory tax rate	34.00%	34.00%	34.00%
State taxes, net of federal benefits	1.38%	0.96%	(3.62%)
Stock-based compensation	(0.16%)	(0.62%)	(1.20%)
Credits	1.99%	1.46%	3.30%
Other	(0.64%)	(0.10%)	(0.54%)
Valuation allowance	(4.03%)	(26.22%)	(31.94%)
Warrant valuation	(0.00%)	(9.48%)	(0.00%)
Tax rate change	(32.54%)	0.00%	0.00%
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, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carry forwards	$ 68,807	$ 71,858
Research and development credit	17,365	10,969
Intangible assets	824	1,653
Depreciation		191
Temporary differences	8,017	4,682
Gross Deferred tax assets	95,013	89,353
Less: valuation allowance	$ (95,013)	$ (89,353)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes Disclosure [Line Items]
Increase (decrease) in valuation allowance		$ 5,700,000	$ 18,700,000
Unrecognized tax benefits that would impact effective tax rate		1,700,000	$ 1,000,000	$ 800,000
Unrecognized tax benefit, penalties and interest accrued		$ 0
Tax rate		34.00%	34.00%	34.00%
Estimate of effects of Tax Cuts and Job act on deferred tax balances		$ 40,900,000
Scenario, Forecast
Income Taxes Disclosure [Line Items]
Tax rate	21.00%
Domestic Tax Authority
Income Taxes Disclosure [Line Items]
Operating loss carryforwards		$ 297,500,000
Operating loss carryforwards expiration start year		2,023
State and Local Jurisdiction
Income Taxes Disclosure [Line Items]
Operating loss carryforwards		$ 85,000,000
Operating loss carryforwards expiration start year		2,018
Research Tax Credit Carryforward | Domestic Tax Authority
Income Taxes Disclosure [Line Items]
Tax credit carryforward		$ 13,800,000
Tax credit carryforward expiration start year		2,025
Research Tax Credit Carryforward | State and Local Jurisdiction
Income Taxes Disclosure [Line Items]
Tax credit carryforward		$ 7,200,000

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefit Changes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrecognized Tax Benefit
Balance at beginning of year	$ 1,197	$ 957
Increase related to current year tax provision	516	240	$ 162
Increase related to tax rate change	144
Increase related to prior year tax provision			795
Balance at end of year	$ 1,857	$ 1,197	$ 957

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($) $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2015	Jan. 31, 2011	Dec. 31, 2010	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	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				$ 0.9	$ 0.5	$ 0.3

Related-Party Transactions - Ad

Related-Party Transactions - Additional Information (Details) - USD ($)	Jun. 03, 2016	Aug. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Warrants to purchase common stock, exercise price				$ 3.78
Proceeds from warrant exercises			$ 1,200,000	$ 418,000	$ 1,151,000
Exercise of warrants to purchase common stock			707,269
Common Stock
Related Party Transaction [Line Items]
Shares issued					907,711	197,838
Private Placement
Related Party Transaction [Line Items]
Proceeds from issuance or sale of equity	$ 25,400,000
Warrants to purchase common stock, exercise price	$ 3.66
Weighted average contractual term	5 years
Private Placement | Chief Executive Officer
Related Party Transaction [Line Items]
Shares issued	141,453
Number of shares authorized to be purchased	35,363
Proceeds from issuance or sale of equity	$ 500,000
Private Placement | Chief Operating Officer
Related Party Transaction [Line Items]
Proceeds from warrant exercises		$ 129,429
Private Placement | Common Stock
Related Party Transaction [Line Items]
Shares issued	7,999,996				7,999,996
Number of shares authorized to be purchased	1,999,999
Private Placement | Common Stock | Chief Operating Officer
Related Party Transaction [Line Items]
Exercise of warrants to purchase common stock		35,363
Private Placement | Maximum
Related Party Transaction [Line Items]
Weighted average contractual term	5 years

Subsequent Events - Additional

Subsequent Events - Additional Information (Details)	Feb. 26, 2018USD ($)Installment	Aug. 05, 2015	Jan. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Feb. 27, 2018USD ($)shares
Subsequent Event [Line Items]
Repayment of loan payable				$ 4,167,000
Secured Debt
Subsequent Event [Line Items]
Variable interest rate (percent)		1.00%
Subsequent Event
Subsequent Event [Line Items]
2018 Shelf Registration statement, offering amount					$ 250,000,000
Subsequent Event | Secured Debt
Subsequent Event [Line Items]
Repayment of loan payable	$ 20,900,000
Subsequent Event | Silicon Valley Bank
Subsequent Event [Line Items]
Loan commitment fee	6.00%
Compensating cash balance	$ 48,000,000
Subsequent Event | Silicon Valley Bank | Term Loan A
Subsequent Event [Line Items]
Loan	$ 25,000,000
Debt, term (in years)	5 years
Interest rate, floating	3.00%
Interest-only payment date	Feb. 29, 2020
Loan payment, number of consecutive equal monthly installments of principal | Installment	36
Subsequent Event | Silicon Valley Bank | Term Loan A | Prime Rate
Subsequent Event [Line Items]
Variable interest rate (percent)	(1.50%)
Subsequent Event | Silicon Valley Bank | Term Loan B
Subsequent Event [Line Items]
Debt, term (in years)	4 years
Loan available to draw	$ 25,000,000
Loan to draw after the Closing date, period (in months)	12 months
Interest rate, floating	5.50%
Loan commitment fee on unused amount	1.00%
Interest-only payment period	24 months
Loan payment, number of consecutive equal monthly installments of principal | Installment	24
Subsequent Event | Silicon Valley Bank | Term Loan B | Prime Rate
Subsequent Event [Line Items]
Variable interest rate (percent)	1.00%
ATM equity offering program
Subsequent Event [Line Items]
Shares issued | shares				1,105,549
Proceeds from issuance of common stock, gross of issuance costs				$ 5,300,000
Proceeds from sale of stock, net of commissions and other transaction costs				$ 5,100,000
ATM equity offering program | Subsequent Event
Subsequent Event [Line Items]
2018 Shelf Registration statement, offering amount					$ 50,000,000
Weighted Average | ATM equity offering program
Subsequent Event [Line Items]
Share price (dollars per share) | $ / shares				$ 4.82
Cowen and Company, LLC | ATM equity offering program | Subsequent Event
Subsequent Event [Line Items]
Shares issued | shares			2,144,454
Proceeds from issuance of common stock, gross of issuance costs			$ 24,700
Proceeds from sale of stock, net of commissions and other transaction costs			$ 24,000
Shares remain available for sale under sales agreement | shares					0
Cowen and Company, LLC | Weighted Average | ATM equity offering program | Subsequent Event
Subsequent Event [Line Items]
Share price (dollars per share) | $ / shares			$ 11.51

Selected Unaudited Quarterly 73

Selected Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Contract revenue	$ 1,869	$ 577	$ 1,266	$ 7,463	$ 10,734	$ 16,046	$ 9,144	$ 5,849	$ 11,175	$ 41,773	$ 26,061
Operating expenses	43,973	37,121	31,059	25,348	22,796	24,996	25,659	17,670	137,501	91,121	52,634
Other income (expense), net	5,722	6,637	3,723	(15,374)	(17,662)	(2,088)	(1,753)	(376)	1,635	300	198
Net loss	$ (36,382)	$ (29,907)	$ (26,070)	$ (33,259)	$ (29,724)	$ (11,038)	$ (18,268)	$ (12,197)	$ (125,618)	$ (71,227)	$ (27,093)
Net loss per common share:
Basic	$ (0.86)	$ (0.71)	$ (0.68)	$ (0.93)	$ (1.04)	$ (0.41)	$ (0.87)	$ (0.66)
Diluted	$ (0.98)	$ (0.85)	$ (0.78)	$ (0.93)	$ (1.04)	$ (0.41)	$ (0.87)	$ (0.66)
Weighted-average shares used to calculate net loss per common share:
Basic	42,422,592	42,259,001	38,072,763	35,725,876	28,653,045	26,789,397	20,899,297	18,398,288
Diluted	43,257,602	43,211,059	39,092,279	35,725,876	28,653,045	26,789,397	20,899,297	18,398,288