Cidara Therapeutics (CDTX) 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. 20, 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	CDTX
Entity Registrant Name	Cidara Therapeutics, Inc.
Entity Central Index Key	1,610,618
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		20,771,151
Entity Public Float			$ 102.8

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 60,813	$ 85,367
Short-term investments	14,501	19,252
Accounts receivable	321	0
Prepaid expenses and other current assets	2,035	779
Total current assets	77,670	105,398
Property and equipment, net	1,044	1,374
Other assets	321	190
Total assets	79,035	106,962
Current liabilities:
Accounts payable	2,590	2,909
Accrued liabilities	4,257	3,338
Accrued compensation and benefits	2,571	2,662
Current portion of term loan	2,667	0
Total current liabilities	12,085	8,909
Term loan, less debt issuance costs	7,206	9,794
Other long-term liabilities	0	80
Total liabilities	19,291	18,783
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized and no shares issued or outstanding at December 31, 2017 and 2016, respectively	0	0
Common stock, $0.0001 par value; 200,000,000 shares authorized at December 31, 2017 and 2016; 20,534,993 and 20,525,688 shares issued and outstanding, respectively, at December 31, 2017; 16,837,126 and 16,773,232 shares issued and outstanding, respectively, at December 31, 2016	2	2
Additional paid-in capital	209,140	181,840
Accumulated other comprehensive loss	(8)	(1)
Accumulated deficit	(149,390)	(93,662)
Total stockholders' equity	59,744	88,179
Total liabilities and stockholders' equity	$ 79,035	$ 106,962

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	20,534,993	16,837,126
Common stock, shares outstanding (in shares)	20,525,688	16,773,232

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ 42,823	$ 35,699	$ 23,475
General and administrative	12,898	12,737	8,838
Total operating expenses	55,721	48,436	32,313
Loss from operations	(55,721)	(48,436)	(32,313)
Other income (expense):
Interest income (expense), net	(7)	271	120
Total other income (expense)	(7)	271	120
Net loss	(55,728)	(48,165)	(32,193)
Other comprehensive income (loss):
Unrealized gain (loss) on short-term investments	(7)	7	(8)
Comprehensive loss	$ (55,735)	$ (48,158)	$ (32,201)
Basic and diluted net loss per share (USD per share)	$ (3.18)	$ (3.32)	$ (3.25)
Shares used to compute basic and diluted net loss per share (in shares)	17,500,853	14,488,987	9,920,382

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	IPO	IPOSeries A Convertible Preferred Stock	IPOSeries B Convertible Preferred Stock	Common Stock	Common StockIPO	Additional Paid-In Capital	Additional Paid-In CapitalIPO	Accumulated Deficit	Other Comprehensive Income (Loss)
Balance, beginning (in shares) at Dec. 31, 2014		97,526,081	0				1,132,738
Balance, beginning at Dec. 31, 2014	$ (11,445)	$ 32,548	$ 0				$ 0		$ 1,859		$ (13,304)	$ 0
Issuance of stock (in shares)			94,533,183				4,800,000
Issuance of stock	69,271		$ 41,921						69,271
Conversion of Series A and Series B convertible preferred upon initial public offering (in shares)					(97,526,081)	(94,533,183)		7,561,380
Conversion of Series A and Series B convertible preferred upon initial public offering				$ 74,469	$ (32,548)	$ (41,921)		$ 1		$ 74,468
Stock-based compensation	3,033								3,033
Vesting of restricted shares (in shares)							249,465
Vesting of restricted shares	499								499
Issuance of common stock for exercise of stock options (in shares)							23,538
Issuance of common stock for exercise of stock options	61								61
Issuance of common stock under Employee Stock Purchase Plan (in shares)							19,164
Issuance of common stock under Employee Stock Purchase Plan	225								225
Issuance of warrants in connection with term loan	0
Unrealized gain (loss) on marketable securities	(8)											(8)
Net loss	(32,193)										(32,193)
Balance, ending (in shares) at Dec. 31, 2015		0	0				13,786,285
Balance, ending at Dec. 31, 2015	103,912	$ 0	$ 0				$ 1		149,416		(45,497)	(8)
Issuance of stock (in shares)							2,752,637
Issuance of stock	26,622						$ 1		26,621
Stock-based compensation	4,344								4,344
Vesting of restricted shares (in shares)							90,423
Vesting of restricted shares	197								197
Issuance of common stock for exercise of stock options (in shares)							83,353
Issuance of common stock for exercise of stock options	525								525
Issuance of common stock under Employee Stock Purchase Plan (in shares)							58,616
Issuance of common stock under Employee Stock Purchase Plan	562								562
Issuance of warrants in connection with term loan	175								175
Unrealized gain (loss) on marketable securities	7											7
Net loss	(48,165)										(48,165)
Balance, ending (in shares) at Dec. 31, 2016		0	0				16,771,314
Balance, ending at Dec. 31, 2016	88,179	$ 0	$ 0				$ 2		181,840		(93,662)	(1)
Issuance of stock (in shares)							3,600,178
Issuance of stock	20,771						$ 0		20,771
Stock-based compensation	5,696								5,696
Vesting of restricted shares (in shares)							19,055
Vesting of restricted shares	$ 44								44
Issuance of common stock for exercise of stock options (in shares)	38,332						38,332
Issuance of common stock for exercise of stock options	$ 228								228
Issuance of common stock for restricted share units vested (in shares)							2,500
Issuance of common stock for restricted share units vested	18								18
Issuance of common stock under Employee Stock Purchase Plan (in shares)							94,309
Issuance of common stock under Employee Stock Purchase Plan	543								543
Issuance of warrants in connection with term loan	0
Unrealized gain (loss) on marketable securities	(7)											(7)
Net loss	(55,728)										(55,728)
Balance, ending (in shares) at Dec. 31, 2017		0	0				20,525,688
Balance, ending at Dec. 31, 2017	$ 59,744	$ 0	$ 0				$ 2		$ 209,140		$ (149,390)	$ (8)

Consolidated Statements of Con6

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Series B Convertible Preferred Stock
Issuance costs	$ 99

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net loss	$ (55,728)	$ (48,165)	$ (32,193)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	667	732	461
Stock-based compensation	5,714	4,344	3,033
Non-cash interest expense	61	17	0
Amortization of discount or premium on short-term investments	(33)	(176)	(42)
Amortization of debt issue costs	18	5	22
Deferred rent	(29)	(8)	54
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,481)	(76)	(487)
Accounts payable and accrued liabilities	642	1,913	2,143
Accrued compensation	453	1,760	1,050
Other assets	(193)	(117)	0
Net cash used in operating activities	(49,909)	(39,771)	(25,959)
Investing activities:
Purchases of short-term investments	(19,523)	(69,617)	(54,918)
Maturities of short-term investments	24,300	95,500	10,000
Purchases of property and equipment	(306)	(401)	(1,170)
Net cash provided by (used in) investing activities	4,471	25,482	(46,088)
Financing activities:
Proceeds from issuance of common stock, net of offering costs	20,735	26,622	69,505
Proceeds from issuance of Term Loan, net of offering costs	0	9,947	0
Proceeds from exercise of stock options	228	525	387
Repurchase of unvested restricted stock	(79)	0	0
Net cash provided by financing activities	20,884	37,094	111,813
Net increase (decrease) in cash and cash equivalents	(24,554)	22,805	39,766
Cash and cash equivalents at beginning of year	85,367	62,562	22,796
Cash and cash equivalents at end of year	60,813	85,367	62,562
Supplemental disclosure of cash flows:
Interest paid	511	0	0
Non-cash investing activity:
Property and equipment acquired but not yet paid	30	21	113
Non-cash financing activities:
Deferred initial public offering costs	0	0	234
Issuance of warrants to purchase common stock upon execution of term loan	0	175	0
Vesting of early exercised stock options	44	197	499
Purchase of shares pursuant to Employee Stock Purchase Plan	543	562	0
Receivable for issuance of common stock, net of offering costs	36	0	0
Series A Convertible Preferred Stock
Non-cash financing activities:
Conversion of convertible preferred stock to common upon initial public offering	0	0	32,548
Series B Convertible Preferred Stock
Financing activities:
Proceeds from issuance of Series B convertible preferred stock, net of offering costs	0	0	41,921
Non-cash financing activities:
Conversion of convertible preferred stock to common upon initial public offering	$ 0	$ 0	$ 41,921

The Company and Basis of Presen

The Company and Basis of Presentation	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company and Basis of Presentation	THE COMPANY AND BASIS OF PRESENTATION Description of Business Cidara Therapeutics, Inc., or the Company, was originally incorporated in Delaware in December 2012 as K2 Therapeutics, Inc., and its name was changed to Cidara Therapeutics, Inc. in July 2014. The Company is a biotechnology company focused on the discovery, development and commercialization of novel anti-infectives. In March 2016, the Company formed a wholly-owned subsidiary, Cidara Therapeutics UK Limited, in England for the purpose of developing its product candidates in Europe. Basis of Presentation The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The Company has experienced net losses and negative cash flows from operating activities since its inception. At December 31, 2017 , the Company had an accumulated deficit of $149.4 million . The Company expects to continue to incur net losses into the foreseeable future. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. In accordance with ASU 2014-15, management is required to perform a two-step analysis over its ability to continue as a going concern. Management must first evaluate whether there are conditions and events that raise substantial doubt about the Company's ability to continue as a going concern (step 1). If management concludes that substantial doubt is raised, management is also required to consider whether its plans alleviate that doubt (step 2). The evaluation period is through one year beyond the date the financial statements were released (assumed to be through February 28, 2019). The Company has prepared cash flow forecasts which indicate, based on the Company’s current cash resources available, that the Company will have sufficient resources to fund its business for at least the next 12 months from the issuance of the financial statements. The Company plans to continue to fund its losses from operations and capital funding needs through debt and equity financing, through government funding or through collaborations or partnerships with other entities. Debt or equity financing, government funding or collaborations and partnerships with other entities may not be available on a timely basis on terms acceptable to the Company, or at all. Management has developed a plan to implement cost cutting measures to reduce its working capital requirements over the next 12 months if an adequate level of financing is not secured. The plan includes the delay of certain of the Company’s development activities, a delay in hiring and a reduction of other discretionary expenditures that are within the Company’s control. Any of the actions contemplated by the implementation of this plan, if required, could have an adverse impact on the Company’s ability to achieve certain of its planned objectives during 2018, and thus, materially harm the Company’s business. Basis of Consolidation — The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All significant intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates —The preparation of financial statements in conformity with U.S. generally accepted accounting principles, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The Company evaluates its estimates and assumptions on an ongoing basis. The most significant estimates in the Company’s consolidated financial statements relate to estimating the fair value of the Company’s common shares used to account for share-based compensation and certain accruals, including those related to preclinical and clinical activities. Although the estimates are based on the Company’s knowledge of current events, comparable companies, and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. Segment Information —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, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Cash and Cash Equivalents —The Company considers all short-term investments purchased with a maturity of three months or less when acquired to be cash equivalents. Investments Available-for-Sale — Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive income (loss). The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. The amortization of premiums and accretion of discounts is included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. Securities with maturity dates of 12 months or less from the date of purchase are classified as short-term investments and securities with maturity dates of more than 12 months are classified as long-term investments. Property and Equipment — The Company records property and equipment at cost, which consists of lab equipment, computer equipment and software, office equipment, furniture and fixtures and leasehold improvements. Property and equipment is depreciated using the straight-line method over the estimated useful lives (generally three to seven years). Leasehold improvements are amortized over the lesser of their useful life or the remaining lease term, including any renewal periods that are deemed to be reasonably assured. Repair and maintenance costs are expensed as incurred. Concentration of Credit Risk —The Company’s financial instruments that are exposed to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. Periodically, the Company maintains deposits in government insured financial institutions in excess of government insured limits. The Company invests its cash balances in financial institutions that it believes have high credit quality, has not experienced any losses on such accounts and does not believe it is exposed to significant credit risk. Patent Costs — The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included in general and administrative expenses in the accompanying statements of operations. Income Taxes —The Company follows the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 740, Income Taxes , or ASC 740, in reporting deferred income taxes. The ASC 740 requires a company to recognize deferred tax assets and liabilities for expected future income tax consequences of events that have been recognized in the Company’s consolidated financial statements. Under this method, deferred tax assets and liabilities are determined based on temporary differences between financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates in the years in which the temporary differences are expected to reverse. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions pursuant to ASC 740, which prescribes a recognition threshold and measurement process for financial statement recognition of uncertain tax positions taken or expected to be taken in a tax return. If the tax position meets this threshold, the benefit to be recognized is measured as the tax benefit having the highest likelihood of being realized upon ultimate settlement with the taxing authority. The Company recognizes interest accrued related to unrecognized tax benefits and penalties in the provision for income taxes. On December 22, 2017, the U.S. enacted the Tax Cuts and Jobs Act (the “Act”), which among other provisions, reduced the U.S. corporate tax rate from 35% to 21%, effective January 1, 2018. At December 31, 2017, we have not completed our accounting for the tax effects of enactment of the Act; however we have made reasonable estimates of the effects on the existing deferred tax assets and liabilities. Revenue Recognition —The Company recognizes revenues when all four of the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectibility is reasonably assured. Grant Funding —The Company has received research and development funding through a grant from a nonprofit organization. The Company has evaluated the terms of the grant to assess its obligations and the classification of funding received. Amounts billable for funded research and development are recognized in the statement of operations as a reduction to research and development expense over the grant period as the related costs are incurred to meet the Company's obligations. Research and Development Costs —Research and development expenses consist of wages, benefits and stock-based compensation charges for research and development employees, scientific consultant fees, facilities and overhead expenses, laboratory supplies, manufacturing expenses, and preclinical and clinical trial costs. The Company accrues preclinical and clinical trial expenses based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of studies, and other events. Costs incurred in purchasing technology assets and intellectual property are charged to research and development expense if the technology has not been conclusively proven to be feasible and has no alternative future use. Comprehensive Loss —Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. The Company’s only component of other comprehensive loss is unrealized gains (losses) on marketable securities. Comprehensive gains (losses) have been reflected in the consolidated statements of operations and comprehensive loss and as a separate component of the statements of convertible preferred stock and stockholders’ equity (deficit) for all periods presented. Stock-based Compensation — The Company accounts for stock-based compensation expense related to employee stock options and employee stock purchase plan rights by estimating the fair value on the date of grant using the Black-Scholes option pricing model. The fair value of Restricted Stock Units (RSUs) and Performance-based RSUs (PRSUs) granted to employees is estimated based on the closing price of the Company's common stock on the date of grant. For awards subject to time-based vesting conditions, stock-based compensation expense is recognized ratably over the requisite service period of the awards. For awards subject to performance-based vesting conditions, the Company assesses the probability of achievement of the individual milestones under the stock-based awards and recognizes stock-based compensation expense over the implicit service period commencing once the Company believes the performance criteria is probable of achievement. The Company accounts for stock options, RSUs, and PRSUs granted to non-employees using the fair value approach. These stock-based awards are subject to periodic revaluation over their vesting terms. Net Loss Per Share —Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of convertible preferred stock, unvested restricted common stock subject to repurchase, warrants, and RSUs and options outstanding under the Company’s stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in common stock equivalent shares): December 31, 2017 2016 Common stock options and RSUs issued and outstanding 3,099,173 2,295,393 Common stock warrants 17,331 17,331 Common stock subject to repurchase 9,305 63,894 Total 3,125,809 2,376,618 Fair Value of Financial Instruments — The Company follows authoritative guidance with respect to fair value reporting issued by the FASB for financial assets and liabilities, which defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The Company’s financial instruments consist of cash and cash equivalents, marketable securities, accounts receivable, prepaid expenses, accounts payable, accrued liabilities and long-term debt. Fair value estimates of these instruments are made at a specific point in time based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, accounts receivable, prepaid expenses, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. The fair value of short-term investments is based upon market prices quoted on the last day of the fiscal period or other observable market inputs. The Company believes that the fair value of long-term debt approximates its carrying value. Recently Issued Accounting Standards — During 2014, the FASB issued ASU 2014-09, "Revenue from Contracts with Customers (Topic 606)," which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Numerous ASUs were issued in 2016 and 2017 to require additional disclosures, to provide clarification on a number of specific issues pertaining to ASU 2014-09, and to defer the effective date for ASU 2014-09 to interim and annual periods beginning after December 31, 2017. The Company has evaluated the impact of ASU 2014-09 on the CARB-X Subaward Agreement and based on the analysis, the Company determined that the pattern of recognition would not be impacted by the adoption of ASC 606 and that characterizing revenues under the Agreement as a reduction of research and development continues to be appropriate after the adoption of ASC 606. The Company will continue to assess any new contracts for revenue recognition under ASU 2014-09. The Company will adopt ASU 2014-09 in the first quarter of 2018, and adoption of this guidance will not have a material impact on the Company's consolidated financial statements. During 2016, the FASB issued ASU 2016-01, “ Recognition and Measurement of Financial Assets and Financial Liabilities ,” which eliminates the requirement for public companies to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet. The standard also requires public entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes. Furthermore, the standard requires presentation of assets and liabilities by measurement category and form of financial asset on the balance sheet or accompanying notes to the financial statements. The updated guidance is effective for interim and annual periods beginning after December 15, 2017, and early adoption is permitted. The Company is currently assessing the impact that this standard will have on its consolidated financial statements. During 2016, the FASB issued ASU 2016-02, “ Lea ses,” which requires that lease arrangements longer than 12 months result in an entity recognizing an asset and liability. The updated guidance is effective for interim and annual periods beginning after December 15, 2018, and early adoption is permitted. The Company currently expects that its operating lease commitments will be subject to the new standard and recognized as right-of-use assets and operating lease liabilities upon the adoption of ASU 2016-02, which will increase the total assets and total liabilities that it reports relative to such amounts prior to adoption. During 2016, the FASB issued ASU 2016-15, " Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments, " which addresses the presentation and classification of certain cash receipts and payments in the statement of cash flows. The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2017, and early adoption is permitted. The adoption of this guidance is not expected to have a material impact on the Company's consolidated financial statements. During 2017, the FASB issued ASU 2017-09, " Compensation - Stock Compensation: Scope of Modification Accounting ," which provides clarity and guidance around which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The standard is effective for interim and annual periods beginning after December 15, 2017. The adoption of this guidance is not expected to have a material impact on the Company's financial statements. During 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The objectives of ASU 2017-12 are to improve the financial reporting of hedging relationships to better portray the economic results of an entity's risk management activities in its financial statements and to make certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018. The adoption of this guidance is not expected to have a material impact on the Company's financial statements.

Short-Term Investments

Short-Term Investments	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Short-Term Investments	SHORT-TERM INVESTMENTS The following table summarizes the available-for-sale securities held at December 31, 2017 and 2016 (in thousands): As of December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate debt $ 14,509 $ — $ (8 ) $ 14,501 Total $ 14,509 $ — $ (8 ) $ 14,501 As of December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Commercial paper 19,253 1 (2 ) 19,252 Total $ 19,253 $ 1 $ (2 ) $ 19,252 All available-for-sale securities held at December 31, 2017 and 2016 mature in less than one year. Unrealized gains and losses on available-for-sale securities are included as a component of other comprehensive income (loss). The securities in unrealized loss positions have not been in a continuous unrealized loss position for 12 months or longer. The Company does not intend to sell the investments and it is not more likely than not that the Company will be required to sell the investments before recovery of their amortized cost bases, which may be at maturity. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS The Company follows ASC 820-10, Fair Value Measurements and Disclosures , which among other things, defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-tier fair value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions, which reflect those that a market participant would use. The Company classifies investments in money market funds within Level 1 as the prices are available from quoted prices in active markets. Investments in commercial paper, corporate debt and reverse repurchase agreements are classified within Level 2 as these instruments are valued using observable market inputs including reported trades, broker/dealer quotes, bids and/or offers. None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented. The following tables summarize the Company’s financial instruments measured at fair value on a recurring basis (in thousands): TOTAL LEVEL 1 LEVEL 2 LEVEL 3 December 31, 2017 Assets: Money market funds $ 11,556 $ 11,556 $ — $ — U.S Treasury reverse repurchase agreements 48,000 — 48,000 — Corporate debt 15,101 — 15,101 — Total assets at fair value $ 74,657 $ 11,556 $ 63,101 $ — December 31, 2016 Assets: Money market funds $ 84,830 $ 84,830 $ — $ — Commercial paper $ 19,252 — 19,252 — Total assets at fair value $ 104,082 $ 84,830 $ 19,252 $ —

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment	PROPERTY AND EQUIPMENT Property and equipment consisted of the following (in thousands): December 31, 2017 2016 Laboratory equipment $ 2,051 $ 1,771 Leasehold improvements 425 425 Computer hardware and software 327 295 Office equipment 119 111 Furniture and fixtures 142 142 3,064 2,744 Less accumulated depreciation and amortization (2,020 ) (1,370 ) Total $ 1,044 $ 1,374 Depreciation and amortization of property and equipment of $667,000 and $732,000 were recorded for the years ended December 31, 2017 and 2016 , respectively.

Debt

Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt	DEBT Term Loans On October 3, 2016, the Company entered into a loan and security agreement, (the "Loan Agreement"), with Pacific Western Bank, as the collateral agent and a lender (the "Lender"), pursuant to which the Lender agreed to lend to the Company up to $20.0 million in a series of term loans. Contemporaneously, the Company borrowed $10.0 million from the Lender (the "Term A Loan"). Under the terms of the Loan Agreement and subject to the achievement of positive Phase 2 clinical results from the STRIVE Phase 2 clinical trial of rezafungin acetate, formerly known as CD101, by March 31, 2018 (the "Milestone"), the Company may, at its sole discretion through October 3, 2018, borrow from the Lender up to an additional $10.0 million (the "Term B Loan", and together with Term A Loan, the "Term Loans"). The Company’s obligations under the Loan Agreement are secured by a first priority security interest in substantially all of the Company’s current and future assets, other than its intellectual property, which is subject to a double negative pledge. The Term Loans mature on October 3, 2020 (the "Maturity Date"). Payments under the Term Loans will be interest-only through April 2, 2018 , which will be extended by six months if the Milestone is achieved. The interest-only period will be followed by 30 equal monthly payments of principal and interest; provided that there will be 24 equal monthly payments if the Milestone is achieved. The Term Loans will bear interest at a variable annual rate equal to the greater of (i) 4.5% or (ii) the Lender’s prime interest rate plus 1.0% . At December 31, 2017 , the Term Loans bear interest at 5.5% . The Company may prepay the borrowed amounts, provided that the Company will be obligated to pay a prepayment fee equal to (i) 2.0% of the applicable principal amount of the Term Loan if the prepayment occurs before the first anniversary of the applicable funding date, and (ii) 1.0% of the applicable principal amount of the Term Loan if the prepayment occurs after the first anniversary of the funding date of such Term Loan but on or prior to the second anniversary of the funding date of such Term Loan. Pursuant to the Loan Agreement, on October 3, 2016, the Company issued to the Lender a warrant to purchase an aggregate of up to 17,331 shares of the Company’s common stock at an exercise price of $11.54 per share. If the Company borrows additional amounts under the Loan Agreement, it will, in connection with any such borrowing, issue the Lender an additional warrant to purchase that number of shares of the Company’s common stock as is equal to 2.0% of the additional principal amount borrowed divided by the exercise price. The exercise price shall be equal to the 30 -day average closing price of the Company’s common stock, calculated as of the date immediately prior to the date of such additional borrowing. The warrants are immediately exercisable and will expire ten years from the date of the grant. While any amounts are outstanding under the Loan Agreement, the Company is subject to a number of affirmative and restrictive covenants, including covenants regarding dispositions of property, business combinations or acquisitions, incurring additional indebtedness and transactions with affiliates, among other customary covenants. The Company is also restricted from paying dividends or making other distributions or payments on its capital stock, subject to limited exceptions. Upon the occurrence of certain events, including but not limited to the Company’s failure to satisfy its payment obligations under the Loan Agreement, the breach of certain of its other covenants under the Loan Agreement, including the receipt of positive Phase 2 clinical data from the rezafungin program by March 31, 2018 , or the occurrence of a material adverse change, the collateral agent will have the right, among other remedies, to declare all principal and interest and other amounts due to the Lender under the Loan Agreement immediately due and payable. As of December 31, 2017 , future principal payments due under the Term A Loan are as follows (in thousands): Year ended: December 31, 2018 $ 2,667 December 31, 2019 4,000 December 31, 2020 3,333 Total future principal payments due under the Term A Loan $ 10,000 The fair value of the warrants to purchase common stock issued in connection with Term Loan A was estimated on the date of issuance using the Black-Scholes valuation model and recorded to additional paid-in capital. The fair value of the warrants on the date of issuance as well as the debt issue costs incurred in connection with the entry into the Loan Agreement are presented as a direct deduction from the carrying amount of the term loan on the consolidated balance sheet and are being amortized utilizing the effective interest method over the term of the loan. The Company recorded interest expense for the amortization of the fair value of the warrants and debt issue costs of $78,000 and $22,000 for the years ended December 31, 2017 and 2016 , respectively, for the amortization of the fair value of the warrants and debt issue costs.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	STOCKHOLDERS’ EQUITY Preferred Stock — Under the amended and restated certificate of incorporation, the Company’s board of directors has the authority, without further action by the stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each such series, to fix the rights, preferences and privileges of the shares of each wholly unissued series and any qualifications, limitations or restrictions thereon and to increase or decrease the number of shares of any such series, but not below the number of shares of such series then outstanding. The Company had 10,000,000 shares of preferred stock authorized and no shares of preferred stock issued or outstanding at December 31, 2017 . Common Stock —The Company had 200,000,000 shares of common stock authorized as of December 31, 2017 . Holders of outstanding shares of common stock are entitled to one vote for each share held of record on all matters submitted to a vote of the holders of common stock. Subject to the rights of the holders of any class of the Company’s capital stock having any preference or priority over common stock, the holders of common stock are entitled to receive dividends that are declared by the Company’s board of directors out of legally available funds. In the event of a liquidation, dissolution or winding-up, the holders of common stock are entitled to share ratably in the net assets remaining after payment of liabilities, subject to prior rights of preferred stock, if any, then outstanding. The common stock has no preemptive rights, conversion rights, redemption rights or sinking fund provisions, and there are no dividends in arrears or default. All shares of common stock have equal distribution, liquidation and voting rights, and have no preferences or exchange rights. On October 13, 2016, the Company completed a public offering of common stock in which it sold 2,752,637 shares of its common stock at an offering price of $10.10 per share. The Company raised net proceeds of approximately $26.6 million after deducting underwriting discounts and commissions and offering expenses. In October 2017 the Company closed a private placement transaction pursuant to which an aggregate of 3,360,000 shares of common stock were sold at a price of $6.00 per share. The Company received net proceeds of approximately $18.9 million after deducting placement agent fees and offering expenses. In November 2017 the Company began to sell shares of common stock under a controlled equity sales agreement with Cantor Fitzgerald & Co. During the year ended December 31, 2017 , the Company sold 240,178 shares of common stock for net proceeds of approximately $1.8 million after deducting placement agent fees. Common Stock Reserved for Future Issuance Common stock reserved for future issuance is as follows (in common stock equivalent shares): Years ended December 31, 2017 2016 Common stock warrants 17,331 17,331 Stock options issued and outstanding 3,099,173 2,295,393 Authorized for future stock awards 1,006,307 1,404,933 Awards available under the ESPP 380,875 306,813 Total 4,503,686 4,024,470

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Incentive Plans	EQUITY INCENTIVE PLANS 2015 Equity Incentive Plan In March 2015, the Company’s board of directors and stockholders approved and adopted the 2015 Equity Incentive Plan (“2015 EIP”). Under the 2015 EIP, the Company may grant stock options, stock appreciation rights, restricted stock, RSUs, and other awards to individuals who are employees, officers, directors or consultants of the Company. The number of shares of stock available for issuance under the 2015 EIP will be automatically increased each January 1 by 4% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number as determined by the Company’s board of directors. Terms of stock award agreements, including vesting requirements, are determined by the board of directors, subject to the provisions of the 2015 EIP. Stock options granted by the Company generally vest over a three - or four -year period. Certain stock options are subject to acceleration of vesting in the event of certain change of control transactions. The stock options may be granted for a term of up to 10 years from the date of grant. The exercise price for stock options granted under the 2015 EIP must be at a price no less than 100% of the estimated fair value of the shares on the date of grant as determined by the board of directors, provided that for an incentive stock option granted to an employee who at the time of grant owns stock representing more than 10% of the voting power of all classes of stock of the Company, the exercise price shall be no less than 110% of the estimated value on the date of grant. 2015 Employee Stock Purchase Plan In March 2015, the Company’s board of directors and stockholders approved and adopted the 2015 Employee Stock Purchase Plan ("ESPP"). The number of shares of stock available for issuance under the ESPP will be automatically increased each January 1 by the lesser of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, (ii) 490,336 shares, or (iii) such lesser number as determined by the Company’s board of directors. The ESPP allows substantially all employees to purchase the Company’s common stock through a payroll deduction at a price equal to 85% of the lower of the fair market value of the stock as of the beginning or the end of each purchase period. An employee’s payroll deductions under the ESPP are limited to 15% of the employee’s eligible compensation. During the year ended December 31, 2017 , 94,309 shares were issued pursuant to the ESPP. Restricted Stock The Company permits early exercise prior to vesting of certain stock options. Any such unvested exercised shares are restricted and subject to repurchase by the Company until the conditions for vesting are met. At December 31, 2017 and 2016 , the liabilities for the cash received from the early exercise of stock options were $21,000 and $144,000 , respectively, and were classified in accrued liabilities on the balance sheet. The Company reduces the liability as the underlying shares vest in accordance with the vesting terms outlined in the stock option agreements, which generally are 4 years . At December 31, 2017 , 9,305 unvested shares were subject to repurchase by the Company. Restricted Stock Units The following table summarizes RSU and PRSU activity during the year ended December 31, 2017 : Number of Outstanding at December 31, 2016 — RSUs and PRSUs granted 240,000 RSUs and PRSUs vested (2,500 ) RSUs and PRSUs canceled (10,000 ) Outstanding at December 31, 2017 227,500 For the year ended December 31, 2017 , stock-based compensation expense related to RSUs and PRSUs was approximately $95,000 . At December 31, 2017 , estimated unrecognized compensation expense related to RSUs and PRSUs granted to employees was approximately $1.4 million . Stock Options The following table summarizes stock option activity during the year ended December 31, 2017 : Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Life in Years Total Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2016 2,295,393 $ 7.82 8.20 $ 6,774 Options granted 1,043,950 7.76 Options exercised (38,332 ) 5.95 Options canceled (201,838 ) 9.21 Outstanding at December 31, 2017 3,099,173 $ 7.74 8.10 $ 2,264 Vested and expected to vest at December 31, 2017 3,099,173 $ 7.74 8.10 $ 2,264 Exercisable at December 31, 2017 1,860,030 $ 7.15 7.58 $ 2,205 The following table summarizes the Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted to employees under our equity incentive plans and the shares purchasable under our 2015 ESPP during the periods presented: For the years ended December 31, 2017 2016 2015 EIP Risk-free interest rate 1.87% - 2.23% 1.14% - 2.09% Expected dividend yield 0% 0% Expected volatility 79% - 86% 80% - 82% Expected term (years) 5.50 - 6.08 5.50 - 6.08 2015 ESPP Risk-free interest rate 1.05% - 1.77% 0.48% - 1.08% Expected dividend yield 0% 0% Expected volatility 79% - 102% 80% - 107% Expected term (years) 0.50 - 2.00 0.50 - 2.00 Stock-based compensation expense recognized for restricted shares, RSUs, PRSUs, stock options, and the ESPP has been reported in the statements of operations and comprehensive loss as follows (in thousands): Years ended December 31, 2017 2016 Research and development $ 2,428 $ 2,005 General and administrative 3,286 2,339 Total $ 5,714 $ 4,344 The weighted-average grant date fair value of stock options granted to employees during the year ended December 31, 2017 was $5.54 per share. The total grant date fair value of stock options that vested during the year ended December 31, 2017 was $4.9 million . As of December 31, 2017 , total unrecognized share-based compensation expense related to unvested employee stock options of the Company was approximately $7.6 million . This unrecognized compensation cost is expected to be recognized over a weighted-average period of approximately 1.92 years. As of December 31, 2017 , total unrecognized compensation expense related to the Company’s ESPP was approximately $0.6 million . This unrecognized compensation cost is expected to be recognized over approximately 1.0 years.

Significant Agreements and Cont

Significant Agreements and Contracts	12 Months Ended
	Dec. 31, 2017
Deferred Revenue Disclosure [Abstract]
Significant Agreements and Contracts	SIGNIFICANT AGREEMENTS AND CONTRACTS Combating Antibiotic Resistant Bacteria Accelerator (CARB-X) Subaward Agreement On March 30, 2017, the Company entered into a Cost Reimbursement Research Subaward Agreement (the "Subaward Agreement") with the Trustees of Boston University. Under the Subaward Agreement, the Company is a subawardee under the CARB-X program. CARB-X is a public-private partnership focused on antibacterials, created by the U.S. Department of Health and Human Services (HHS), Biomedical Advanced Research and Development Authority (BARDA), and National Institute of Allergy and Infectious Diseases (NIAID). CARB-X is funded by BARDA and the London-based Wellcome Trust, a global charitable foundation (Wellcome), and administered by the Boston University School of Law. The subaward supports development of the Company's CD201 product candidate. Under the Subaward Agreement, during an initial phase that began on April 1, 2017 and ends upon acceptance by the U.S. Food and Drug Administration of an initial new drug application, CARB-X would reimburse up to $3.9 million of qualifying development expenses. If all of the milestones in such initial phase are met, the CARB-X Joint Oversight Committee will evaluate the progress made in such initial phase and determine whether to exercise its option to fund a second stage. During the second stage, CARB-X would reimburse up to $3.0 million of qualifying development expenses through a Phase 1 clinical trial. Such second stage would be subject to a new subaward agreement. Under the Subaward Agreement, the Company is reimbursed for direct costs incurred plus allowable indirect costs which consist of fringe benefits and allowable general and administrative expenses. For the year ended December 31, 2017 , the Company recognized reductions to research and development expenses of $0.5 million for costs eligible for reimbursement under the Subaward Agreement. As of December 31, 2017 , billed accounts receivable were $0.1 million and unbilled accounts receivable were $0.2 million related to reimbursable expenses under the Subaward Agreement. The Subaward Agreement can be terminated upon the delivery of 30 days written notice to the Company for default or convenience. Upon receipt of a notice of termination, the Company must discontinue contract activities and CARB-X must pay the Company a final settlement based on eligible expenses incurred under the Subaward Agreement. Based on preclinical studies of CD201 as well as preclinical studies of antibody-drug conjugates (ADCs) from the Cloudbreak program, the Company decided in February 2018 to cease development of CD201 to focus on the more promising ADCs for the same indication. Based on the decision to focus efforts on the ADCs, the Company will no longer be seeking funding under the Subaward Agreement relating to CD201.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The Company accounts for income taxes under ASC 740. Deferred income tax assets and liabilities are determined based upon differences between financial reporting and 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 following table provides a reconciliation between income taxes computed at the federal statutory rate of 34% and the provision for income taxes (in thousands): Years Ended December 31, 2017 2016 2015 Federal income taxes at 34% $ (18,947 ) $ (16,334 ) $ (10,946 ) State income tax, net of federal benefit — (1 ) (1,821 ) Tax effect on nondeductible expenses 3,389 1,650 341 Research credits (8,125 ) (3,538 ) (676 ) Rate change — 267 — Change in valuation allowance 5,133 14,996 13,084 Reserve for uncertain tax positions 1,451 2,883 — Tax Cuts and Jobs Act 17,334 — — Other (235 ) 77 18 Income tax expense $ — $ — $ — Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2017 2016 Deferred tax assets: Net operating losses $ 26,364 $ 27,309 Research credits 10,232 3,646 Intangibles 265 466 Other 1,722 2,030 Total deferred tax assets 38,583 33,451 Less valuation allowance (38,583 ) (33,451 ) Income tax expense $ — $ — At December 31, 2017 , the Company had federal and state net operating loss carryforwards of approximately $122.5 million and $81.5 million , respectively. The federal and state loss carryforwards begin to expire in 2033 , unless previously utilized. The Company also has federal research and development and orphan drug credit carryforwards totaling $12.5 million and state research and development credit carryforwards totaling $1.6 million . The federal research and development credit and orphan drug credit carryforwards begin to expire in 2033, unless previously utilized. The state research and development credit carryforwards begin to expire in 2018. Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use the existing deferred tax assets. Based on the weight of all evidence, including a history of operating losses, management has determined that it is more likely than not that the net deferred tax assets will not be realized. A valuation allowance of $38.6 million and $33.5 million as of December 31, 2017 and 2016 , respectively, has been established to offset the deferred tax assets as realization of such assets is uncertain. Future utilization of the Company’s net operating loss and research and development credits carryforwards to offset future taxable income may be subject to an annual limitation, pursuant to Internal Revenue Code (IRC) Sections 382 and 383, as a result of ownership changes that may have occurred or that could occur in the future. An ownership change occurs when a cumulative change in ownership of more than 50% occurs within a three -year period. The Company has not completed an IRC Section 382/383 analysis regarding the limitation of net operating loss and research and development credit carryforwards. The Tax Cuts and Jobs Act was enacted on December 22, 2017. The Act reduces the US 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. At December 31, 2017, the Company has not completed accounting for the tax effects of enactment of the Act; however, in certain cases, as described below, the Company has made a reasonable estimate of the effects on its existing deferred tax balances. For items for which the Company was able to determine a reasonable estimate, it recognized a provisional amount of $17.3 million which was offset by a corresponding reduction to the valuation allowance. In all cases, the Company will continue to make and refine its calculations as additional analysis is completed. In addition, its estimates may also be affected as the Company gains a more thorough understanding of the tax law. The Company recognizes a tax benefit from an uncertain tax position when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. Income tax positions must meet a more likely than not recognition at the effective date to be recognized. At December 31, 2017 and 2016 , the unrecognized tax benefits recorded were approximately $10.8 million and $4.6 million , respectively. Approximately $8.6 million of the unrecognized tax benefits would reduce the Company's annual effective tax rates, if recognized, subject to the valuation allowances. The Company does not anticipate a significant change in the unrecognized tax benefits within the next 12 months. A reconciliation of the beginning and ending amount of gross unrecognized tax benefits for 2017, 2016 and 2015 is as follows (in thousands): Years Ended December 31, 2017 2016 2015 Balance as of the beginning of the year $ 4,642 $ 356 $ 108 Increases related to current year tax positions 3,965 921 248 Increases related to prior year tax positions 2,149 3,365 — Balance as of the end of the year $ 10,756 $ 4,642 $ 356 The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by the United States and state jurisdictions where applicable. There are currently no pending income tax examinations. The Company’s tax years from inception in 2012 are subject to examination by the federal and state tax authorities due to the carryforward of unutilized net operating losses and research and development credits. The Company’s practice is to recognize interest and penalties related to income tax matters in income tax expense. The Company has not recognized interest or penalties since inception.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Litigation —From time to time, the Company may be involved in various lawsuits, legal proceedings, or claims that arise in the ordinary course of business. Management believes there are no claims or actions pending against the Company at December 31, 2017 which will have, individually or in the aggregate, a material adverse effect on its business, liquidity, financial position or results of operations. Litigation, however, is subject to inherent uncertainties, and an adverse result in such matters may arise from time to time that may harm the Company’s business. Lease Obligations —In June 2014, the Company entered into an operating lease agreement for laboratory and office space in San Diego, California. Amendments for additional space were entered into in February 2015, March 2015 and August 2015. The lease expires in December 2018 with options for two individual two -year extensions. The lease is subject to charges for common area maintenance and other costs, and base rent is subject to 3% annual increases every July. Rent expense is being recorded on a straight-line basis over the life of the lease. Future minimum payments required under the lease as of December 31, 2017 are summarized as follows (in thousands): 2018 746 Total minimum lease payments $ 746 Rent expense was $704,000 and $733,000 for the years ended December 31, 2017 and 2016 , respectively. Contractual Obligations —The Company enters into contracts in the normal course of business with vendors for research and development activities, manufacturing, and professional services. These contracts generally provide for termination either on or within 30 days of notice.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events "At-the-market" offering —In November 2017 the Company began to sell shares of common stock under a controlled equity sales agreement with Cantor Fitzgerald & Co. During the period from January 1, 2018 through February 20, 2018 , the Company sold 241,837 shares of common stock for net proceeds of approximately $1.7 million after deducting placement agent fees.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter 2017 Operating expenses $ 13,398 $ 16,615 $ 12,249 $ 13,459 Other income (expense) — (30 ) (8 ) 31 Net loss (13,398 ) (16,645 ) (12,257 ) (13,428 ) Basic and diluted net loss per share $ (0.80 ) $ (0.99 ) $ (0.73 ) $ (0.69 ) Shares used to compute basic and diluted net loss per share 16,795,366 16,831,960 16,864,211 19,489,375 2016 Operating expenses $ 9,885 $ 11,862 $ 12,336 $ 14,353 Other income (expense) 96 107 109 (41 ) Net loss (9,789 ) (11,755 ) (12,227 ) (14,394 ) Basic and diluted net loss per share $ (0.71 ) $ (0.85 ) $ (0.88 ) $ (0.88 ) Shares used to compute basic and diluted net loss per share 13,807,825 13,871,938 13,910,145 16,352,046

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The Company has experienced net losses and negative cash flows from operating activities since its inception. At December 31, 2017 , the Company had an accumulated deficit of $149.4 million . The Company expects to continue to incur net losses into the foreseeable future. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. In accordance with ASU 2014-15, management is required to perform a two-step analysis over its ability to continue as a going concern. Management must first evaluate whether there are conditions and events that raise substantial doubt about the Company's ability to continue as a going concern (step 1). If management concludes that substantial doubt is raised, management is also required to consider whether its plans alleviate that doubt (step 2). The evaluation period is through one year beyond the date the financial statements were released (assumed to be through February 28, 2019). The Company has prepared cash flow forecasts which indicate, based on the Company’s current cash resources available, that the Company will have sufficient resources to fund its business for at least the next 12 months from the issuance of the financial statements. The Company plans to continue to fund its losses from operations and capital funding needs through debt and equity financing, through government funding or through collaborations or partnerships with other entities. Debt or equity financing, government funding or collaborations and partnerships with other entities may not be available on a timely basis on terms acceptable to the Company, or at all.
Basis of Consolidation	Basis of Consolidation — The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All significant intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates —The preparation of financial statements in conformity with U.S. generally accepted accounting principles, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The Company evaluates its estimates and assumptions on an ongoing basis. The most significant estimates in the Company’s consolidated financial statements relate to estimating the fair value of the Company’s common shares used to account for share-based compensation and certain accruals, including those related to preclinical and clinical activities. Although the estimates are based on the Company’s knowledge of current events, comparable companies, and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.
Segment Information	Segment Information —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, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.
Cash and Cash Equivalents	Cash and Cash Equivalents —The Company considers all short-term investments purchased with a maturity of three months or less when acquired to be cash equivalents.
Investments Available-for-Sale	Investments Available-for-Sale — Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive income (loss). The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. The amortization of premiums and accretion of discounts is included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. Securities with maturity dates of 12 months or less from the date of purchase are classified as short-term investments and securities with maturity dates of more than 12 months are classified as long-term investments.
Property and Equipment	Property and Equipment — The Company records property and equipment at cost, which consists of lab equipment, computer equipment and software, office equipment, furniture and fixtures and leasehold improvements. Property and equipment is depreciated using the straight-line method over the estimated useful lives (generally three to seven years). Leasehold improvements are amortized over the lesser of their useful life or the remaining lease term, including any renewal periods that are deemed to be reasonably assured. Repair and maintenance costs are expensed as incurred.
Concentration of Credit Risk	Concentration of Credit Risk —The Company’s financial instruments that are exposed to concentrations of credit risk consist primarily of cash and cash equivalents and short-term investments. Periodically, the Company maintains deposits in government insured financial institutions in excess of government insured limits. The Company invests its cash balances in financial institutions that it believes have high credit quality, has not experienced any losses on such accounts and does not believe it is exposed to significant credit risk.
Patent Costs	Patent Costs — The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included in general and administrative expenses in the accompanying statements of operations.
Income Taxes	Income Taxes —The Company follows the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 740, Income Taxes , or ASC 740, in reporting deferred income taxes. The ASC 740 requires a company to recognize deferred tax assets and liabilities for expected future income tax consequences of events that have been recognized in the Company’s consolidated financial statements. Under this method, deferred tax assets and liabilities are determined based on temporary differences between financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates in the years in which the temporary differences are expected to reverse. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions pursuant to ASC 740, which prescribes a recognition threshold and measurement process for financial statement recognition of uncertain tax positions taken or expected to be taken in a tax return. If the tax position meets this threshold, the benefit to be recognized is measured as the tax benefit having the highest likelihood of being realized upon ultimate settlement with the taxing authority. The Company recognizes interest accrued related to unrecognized tax benefits and penalties in the provision for income taxes. On December 22, 2017, the U.S. enacted the Tax Cuts and Jobs Act (the “Act”), which among other provisions, reduced the U.S. corporate tax rate from 35% to 21%, effective January 1, 2018. At December 31, 2017, we have not completed our accounting for the tax effects of enactment of the Act; however we have made reasonable estimates of the effects on the existing deferred tax assets and liabilities.
Revenue Recognition	Revenue Recognition —The Company recognizes revenues when all four of the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery of the products and/or services has occurred; (3) the selling price is fixed or determinable; and (4) collectibility is reasonably assured. Under the Subaward Agreement, the Company is reimbursed for direct costs incurred plus allowable indirect costs which consist of fringe benefits and allowable general and administrative expenses.
Research and Development Costs and Grant Funding	Grant Funding —The Company has received research and development funding through a grant from a nonprofit organization. The Company has evaluated the terms of the grant to assess its obligations and the classification of funding received. Amounts billable for funded research and development are recognized in the statement of operations as a reduction to research and development expense over the grant period as the related costs are incurred to meet the Company's obligations. Research and Development Costs —Research and development expenses consist of wages, benefits and stock-based compensation charges for research and development employees, scientific consultant fees, facilities and overhead expenses, laboratory supplies, manufacturing expenses, and preclinical and clinical trial costs. The Company accrues preclinical and clinical trial expenses based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of studies, and other events. Costs incurred in purchasing technology assets and intellectual property are charged to research and development expense if the technology has not been conclusively proven to be feasible and has no alternative future use.
Comprehensive Loss	Comprehensive Loss —Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. The Company’s only component of other comprehensive loss is unrealized gains (losses) on marketable securities. Comprehensive gains (losses) have been reflected in the consolidated statements of operations and comprehensive loss and as a separate component of the statements of convertible preferred stock and stockholders’ equity (deficit) for all periods presented.
Stock-based Compensation	Stock-based Compensation — The Company accounts for stock-based compensation expense related to employee stock options and employee stock purchase plan rights by estimating the fair value on the date of grant using the Black-Scholes option pricing model. The fair value of Restricted Stock Units (RSUs) and Performance-based RSUs (PRSUs) granted to employees is estimated based on the closing price of the Company's common stock on the date of grant. For awards subject to time-based vesting conditions, stock-based compensation expense is recognized ratably over the requisite service period of the awards. For awards subject to performance-based vesting conditions, the Company assesses the probability of achievement of the individual milestones under the stock-based awards and recognizes stock-based compensation expense over the implicit service period commencing once the Company believes the performance criteria is probable of achievement. The Company accounts for stock options, RSUs, and PRSUs granted to non-employees using the fair value approach. These stock-based awards are subject to periodic revaluation over their vesting terms.
Net Loss Per Share	Net Loss Per Share —Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of convertible preferred stock, unvested restricted common stock subject to repurchase, warrants, and RSUs and options outstanding under the Company’s stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding.
Fair Value of Financial Instruments	Fair Value of Financial Instruments — The Company follows authoritative guidance with respect to fair value reporting issued by the FASB for financial assets and liabilities, which defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The Company’s financial instruments consist of cash and cash equivalents, marketable securities, accounts receivable, prepaid expenses, accounts payable, accrued liabilities and long-term debt. Fair value estimates of these instruments are made at a specific point in time based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, accounts receivable, prepaid expenses, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. The fair value of short-term investments is based upon market prices quoted on the last day of the fiscal period or other observable market inputs. The Company believes that the fair value of long-term debt approximates its carrying value.
Recently Issued Accounting Standards	Recently Issued Accounting Standards — During 2014, the FASB issued ASU 2014-09, "Revenue from Contracts with Customers (Topic 606)," which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2014-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Numerous ASUs were issued in 2016 and 2017 to require additional disclosures, to provide clarification on a number of specific issues pertaining to ASU 2014-09, and to defer the effective date for ASU 2014-09 to interim and annual periods beginning after December 31, 2017. The Company has evaluated the impact of ASU 2014-09 on the CARB-X Subaward Agreement and based on the analysis, the Company determined that the pattern of recognition would not be impacted by the adoption of ASC 606 and that characterizing revenues under the Agreement as a reduction of research and development continues to be appropriate after the adoption of ASC 606. The Company will continue to assess any new contracts for revenue recognition under ASU 2014-09. The Company will adopt ASU 2014-09 in the first quarter of 2018, and adoption of this guidance will not have a material impact on the Company's consolidated financial statements. During 2016, the FASB issued ASU 2016-01, “ Recognition and Measurement of Financial Assets and Financial Liabilities ,” which eliminates the requirement for public companies to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet. The standard also requires public entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes. Furthermore, the standard requires presentation of assets and liabilities by measurement category and form of financial asset on the balance sheet or accompanying notes to the financial statements. The updated guidance is effective for interim and annual periods beginning after December 15, 2017, and early adoption is permitted. The Company is currently assessing the impact that this standard will have on its consolidated financial statements. During 2016, the FASB issued ASU 2016-02, “ Lea ses,” which requires that lease arrangements longer than 12 months result in an entity recognizing an asset and liability. The updated guidance is effective for interim and annual periods beginning after December 15, 2018, and early adoption is permitted. The Company currently expects that its operating lease commitments will be subject to the new standard and recognized as right-of-use assets and operating lease liabilities upon the adoption of ASU 2016-02, which will increase the total assets and total liabilities that it reports relative to such amounts prior to adoption. During 2016, the FASB issued ASU 2016-15, " Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments, " which addresses the presentation and classification of certain cash receipts and payments in the statement of cash flows. The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2017, and early adoption is permitted. The adoption of this guidance is not expected to have a material impact on the Company's consolidated financial statements. During 2017, the FASB issued ASU 2017-09, " Compensation - Stock Compensation: Scope of Modification Accounting ," which provides clarity and guidance around which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The standard is effective for interim and annual periods beginning after December 15, 2017. The adoption of this guidance is not expected to have a material impact on the Company's financial statements. During 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The objectives of ASU 2017-12 are to improve the financial reporting of hedging relationships to better portray the economic results of an entity's risk management activities in its financial statements and to make certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018. The adoption of this guidance is not expected to have a material impact on the Company's financial statements.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Outstanding Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share	The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in common stock equivalent shares): December 31, 2017 2016 Common stock options and RSUs issued and outstanding 3,099,173 2,295,393 Common stock warrants 17,331 17,331 Common stock subject to repurchase 9,305 63,894 Total 3,125,809 2,376,618

Short-Term Investments (Tables)

Short-Term Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Securities	The following table summarizes the available-for-sale securities held at December 31, 2017 and 2016 (in thousands): As of December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate debt $ 14,509 $ — $ (8 ) $ 14,501 Total $ 14,509 $ — $ (8 ) $ 14,501 As of December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Commercial paper 19,253 1 (2 ) 19,252 Total $ 19,253 $ 1 $ (2 ) $ 19,252

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on Recurring Basis	The following tables summarize the Company’s financial instruments measured at fair value on a recurring basis (in thousands): TOTAL LEVEL 1 LEVEL 2 LEVEL 3 December 31, 2017 Assets: Money market funds $ 11,556 $ 11,556 $ — $ — U.S Treasury reverse repurchase agreements 48,000 — 48,000 — Corporate debt 15,101 — 15,101 — Total assets at fair value $ 74,657 $ 11,556 $ 63,101 $ — December 31, 2016 Assets: Money market funds $ 84,830 $ 84,830 $ — $ — Commercial paper $ 19,252 — 19,252 — Total assets at fair value $ 104,082 $ 84,830 $ 19,252 $ —

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following (in thousands): December 31, 2017 2016 Laboratory equipment $ 2,051 $ 1,771 Leasehold improvements 425 425 Computer hardware and software 327 295 Office equipment 119 111 Furniture and fixtures 142 142 3,064 2,744 Less accumulated depreciation and amortization (2,020 ) (1,370 ) Total $ 1,044 $ 1,374

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Future Principal Payments Due	As of December 31, 2017 , future principal payments due under the Term A Loan are as follows (in thousands): Year ended: December 31, 2018 $ 2,667 December 31, 2019 4,000 December 31, 2020 3,333 Total future principal payments due under the Term A Loan $ 10,000

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Common Stock Reserved for Future Issuance	Common stock reserved for future issuance is as follows (in common stock equivalent shares): Years ended December 31, 2017 2016 Common stock warrants 17,331 17,331 Stock options issued and outstanding 3,099,173 2,295,393 Authorized for future stock awards 1,006,307 1,404,933 Awards available under the ESPP 380,875 306,813 Total 4,503,686 4,024,470

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of RSU and PRSU Activity	The following table summarizes RSU and PRSU activity during the year ended December 31, 2017 : Number of Outstanding at December 31, 2016 — RSUs and PRSUs granted 240,000 RSUs and PRSUs vested (2,500 ) RSUs and PRSUs canceled (10,000 ) Outstanding at December 31, 2017 227,500
Schedule of Stock Option Activity	The following table summarizes stock option activity during the year ended December 31, 2017 : Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Life in Years Total Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2016 2,295,393 $ 7.82 8.20 $ 6,774 Options granted 1,043,950 7.76 Options exercised (38,332 ) 5.95 Options canceled (201,838 ) 9.21 Outstanding at December 31, 2017 3,099,173 $ 7.74 8.10 $ 2,264 Vested and expected to vest at December 31, 2017 3,099,173 $ 7.74 8.10 $ 2,264 Exercisable at December 31, 2017 1,860,030 $ 7.15 7.58 $ 2,205
Summary of Black-Scholes Option Pricing Model Assumptions	The following table summarizes the Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted to employees under our equity incentive plans and the shares purchasable under our 2015 ESPP during the periods presented: For the years ended December 31, 2017 2016 2015 EIP Risk-free interest rate 1.87% - 2.23% 1.14% - 2.09% Expected dividend yield 0% 0% Expected volatility 79% - 86% 80% - 82% Expected term (years) 5.50 - 6.08 5.50 - 6.08 2015 ESPP Risk-free interest rate 1.05% - 1.77% 0.48% - 1.08% Expected dividend yield 0% 0% Expected volatility 79% - 102% 80% - 107% Expected term (years) 0.50 - 2.00 0.50 - 2.00
Summary of Stock-Based Compensation Expense	Stock-based compensation expense recognized for restricted shares, RSUs, PRSUs, stock options, and the ESPP has been reported in the statements of operations and comprehensive loss as follows (in thousands): Years ended December 31, 2017 2016 Research and development $ 2,428 $ 2,005 General and administrative 3,286 2,339 Total $ 5,714 $ 4,344

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Reconciliation Between Federal Statutory and Provision For Income Taxes	The following table provides a reconciliation between income taxes computed at the federal statutory rate of 34% and the provision for income taxes (in thousands): Years Ended December 31, 2017 2016 2015 Federal income taxes at 34% $ (18,947 ) $ (16,334 ) $ (10,946 ) State income tax, net of federal benefit — (1 ) (1,821 ) Tax effect on nondeductible expenses 3,389 1,650 341 Research credits (8,125 ) (3,538 ) (676 ) Rate change — 267 — Change in valuation allowance 5,133 14,996 13,084 Reserve for uncertain tax positions 1,451 2,883 — Tax Cuts and Jobs Act 17,334 — — Other (235 ) 77 18 Income tax expense $ — $ — $ —
Schedule of Components of Net Deferred Tax Assets	Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2017 2016 Deferred tax assets: Net operating losses $ 26,364 $ 27,309 Research credits 10,232 3,646 Intangibles 265 466 Other 1,722 2,030 Total deferred tax assets 38,583 33,451 Less valuation allowance (38,583 ) (33,451 ) Income tax expense $ — $ —
Schedule of Reconciliation Amount of Gross Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of gross unrecognized tax benefits for 2017, 2016 and 2015 is as follows (in thousands): Years Ended December 31, 2017 2016 2015 Balance as of the beginning of the year $ 4,642 $ 356 $ 108 Increases related to current year tax positions 3,965 921 248 Increases related to prior year tax positions 2,149 3,365 — Balance as of the end of the year $ 10,756 $ 4,642 $ 356

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum payments required under the lease as of December 31, 2017 are summarized as follows (in thousands): 2018 746 Total minimum lease payments $ 746

Selected Quarterly Financial 31

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Data (Unaudited)	First Quarter Second Quarter Third Quarter Fourth Quarter 2017 Operating expenses $ 13,398 $ 16,615 $ 12,249 $ 13,459 Other income (expense) — (30 ) (8 ) 31 Net loss (13,398 ) (16,645 ) (12,257 ) (13,428 ) Basic and diluted net loss per share $ (0.80 ) $ (0.99 ) $ (0.73 ) $ (0.69 ) Shares used to compute basic and diluted net loss per share 16,795,366 16,831,960 16,864,211 19,489,375 2016 Operating expenses $ 9,885 $ 11,862 $ 12,336 $ 14,353 Other income (expense) 96 107 109 (41 ) Net loss (9,789 ) (11,755 ) (12,227 ) (14,394 ) Basic and diluted net loss per share $ (0.71 ) $ (0.85 ) $ (0.88 ) $ (0.88 ) Shares used to compute basic and diluted net loss per share 13,807,825 13,871,938 13,910,145 16,352,046

The Company and Basis of Pres32

The Company and Basis of Presentation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit | $	$ 149,390	$ 93,662
Number of operating segments | segment	1

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful lives	3 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful lives	7 years

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	3,125,809	2,376,618
Common stock options and RSUs issued and outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	3,099,173	2,295,393
Common stock warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	17,331	17,331
Common stock subject to repurchase
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	9,305	63,894

Short-Term Investments (Details

Short-Term Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 14,509	$ 19,253
Unrealized Gains	0	1
Unrealized Losses	(8)	(2)
Fair Value	$ 14,501	$ 19,252
Maturity of available-for-sale securities (less than) (term)	1 year	1 year
Corporate debt
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 14,509
Unrealized Gains	0
Unrealized Losses	(8)
Fair Value	$ 14,501
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		$ 19,253
Unrealized Gains		1
Unrealized Losses		(2)
Fair Value		$ 19,252

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - Fair value measurements, nonrecurring - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets	$ 0	$ 0
Fair value of liabilities	$ 0	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - Fair value measurements, recurring basis - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Total assets at fair value	$ 74,657	$ 104,082
Money market funds
Assets:
Asset fair value	11,556	84,830
U.S Treasury reverse repurchase agreements
Assets:
Asset fair value	48,000
Commercial paper
Assets:
Asset fair value		19,252
Corporate debt
Assets:
Asset fair value	15,101
LEVEL 1
Assets:
Total assets at fair value	11,556	84,830
LEVEL 1 | Money market funds
Assets:
Asset fair value	11,556	84,830
LEVEL 1 | U.S Treasury reverse repurchase agreements
Assets:
Asset fair value	0
LEVEL 1 | Commercial paper
Assets:
Asset fair value		0
LEVEL 1 | Corporate debt
Assets:
Asset fair value	0
LEVEL 2
Assets:
Total assets at fair value	63,101	19,252
LEVEL 2 | Money market funds
Assets:
Asset fair value	0	0
LEVEL 2 | U.S Treasury reverse repurchase agreements
Assets:
Asset fair value	48,000
LEVEL 2 | Commercial paper
Assets:
Asset fair value		19,252
LEVEL 2 | Corporate debt
Assets:
Asset fair value	15,101
LEVEL 3
Assets:
Total assets at fair value	0	0
LEVEL 3 | Money market funds
Assets:
Asset fair value	0	0
LEVEL 3 | U.S Treasury reverse repurchase agreements
Assets:
Asset fair value	0
LEVEL 3 | Commercial paper
Assets:
Asset fair value		$ 0
LEVEL 3 | Corporate debt
Assets:
Asset fair value	$ 0

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,064	$ 2,744
Less accumulated depreciation and amortization	(2,020)	(1,370)
Total	1,044	1,374
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,051	1,771
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	425	425
Computer hardware and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	327	295
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	119	111
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 142	$ 142

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation and amortization of property and equipment	$ 667	$ 732	$ 461

Debt - Additional Information (

Debt - Additional Information (Details)	Oct. 03, 2016USD ($)payment$ / sharesshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Shares of common stock issued upon exercise of warrant (in shares) | shares	17,331
Warrants exercise price (in dollars per share) | $ / shares	$ 11.54
Percentage of principal of debt used to calculate number of shares issued by warrant	2.00%
Period of average closing price used to calculate number of shares issued by warrant	30 days
Warrant term	10 years
Term Loan | Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000,000
Extension in interest only payments upon achieving milestone	6 months
Number of payments of principal and interest | payment	30
Number of payments of principal and interest upon achieving milestone | payment	24
Stated interest rate	4.50%	5.50%
Prepayment fee percentage in year one	2.00%
Prepayment fee percentage in year two	1.00%
Term Loan | Loan Agreement | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Term Loan | Term A Loan
Debt Instrument [Line Items]
Debt face amount	$ 10,000,000
Interest expense for the amortization of the fair value of warrants and debt issue costs		$ 78,000	$ 22,000
Term Loan | Term B Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 10,000,000

Debt - Schedule of Future Princ

Debt - Schedule of Future Principal Payments Due (Details) - Term Loan - Term A Loan $ in Thousands	Dec. 31, 2017USD ($)
Year ended:
December 31, 2018	$ 2,667
December 31, 2019	4,000
December 31, 2020	3,333
Total future principal payments due under the Term A Loan	$ 10,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details)	Oct. 13, 2016USD ($)$ / sharesshares	Oct. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2017USD ($)vote_per_shareshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares
Equity [Abstract]
Preferred stock, shares authorized (in shares)			10,000,000	10,000,000
Preferred stock, shares issued (in shares)			0	0
Preferred stock, shares outstanding (in shares)			0	0
Common stock, shares authorized (in shares)			200,000,000	200,000,000
Number of votes entitlement for each share held | vote_per_share			1
Preferred stock, amount of preferred dividends in arrears or default | $			$ 0
Class of Stock [Line Items]
Net proceeds | $			$ 20,771,000	$ 26,622,000	$ 69,271,000
Common Stock
Class of Stock [Line Items]
Issuance of stock (in shares)	2,752,637		3,600,178	2,752,637	4,800,000
Offering price (in dollars per share) | $ / shares	$ 10.10
Net proceeds | $	$ 26,600,000		$ 0	$ 1,000
Private placement
Class of Stock [Line Items]
Common stock sold (in shares)		3,360,000
Price per share (in dollars per share) | $ / shares		$ 6
Net proceeds | $		$ 18,900,000
Controlled equity sales agreement with Cantor Fitzgerald & Co
Class of Stock [Line Items]
Common stock sold (in shares)			240,178
Net proceeds | $			$ 1,800,000

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	4,503,686	4,024,470
Common stock warrants
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	17,331	17,331
Stock options issued and outstanding
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	3,099,173	2,295,393
Authorized for future stock awards
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	1,006,307	1,404,933
Awards available under the ESPP
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	380,875	306,813

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair values of stock options granted (USD per share)	$ 5.54
Grant date fair value of stock options, vested	$ 4,900
Unrecognized share-based compensation expense of unvested employee stock options	$ 7,600
Unvested stock options, unrecognized cost expected to be recognized (in years)	1 year 11 months 1 day
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	3,125,809	2,376,618
Common stock subject to repurchase
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	9,305	63,894
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Automatic annual increase in shares authorized for issuance in equity incentive plan (as a percentage)	1.00%
Price of stock option as percentage of estimated fair value of shares on date of grant (as a percentage)	85.00%
Employee payroll deduction under the stock plan (as a percentage)	15.00%
Issuance of common stock under employee stock purchase plan (in shares)	94,309
Unvested stock options, unrecognized cost expected to be recognized (in years)	1 year
Unrecognized share-based compensation expense of unvested employee stock options	$ 600
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting terms (in years)	4 years
Cash received from early exercise of stock options	$ 21	$ 144
Restricted Stock | Common stock subject to repurchase
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	9,305
Maximum | 2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares outstanding (in shares)	490,336
Authorized for future stock awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Automatic annual increase in shares authorized for issuance in equity incentive plan (as a percentage)	4.00%
Stock options grant period from date of grant (in years)	10 years
Price of stock option as percentage of estimated fair value of shares on date of grant (as a percentage)	100.00%
Employee voting power, percentage (more than)	10.00%
Authorized for future stock awards | More than 10% of voting power
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of stock option as percentage of estimated fair value of shares on date of grant (as a percentage)	110.00%
Authorized for future stock awards | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting terms (in years)	3 years
Authorized for future stock awards | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting terms (in years)	4 years

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of RSU and PRSU Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Stock-based compensation expense	$ 5,714	$ 4,344
RSUs and PRSUs
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, beginning of period (in shares)	0
Granted (in shares)	240,000
Vested (in shares)	(2,500)
Canceled (in shares)	(10,000)
Outstanding, end of period (in shares)	227,500	0
Stock-based compensation expense	$ 95
Unrecognized share-based compensation expense related to RSUs and PRSUs	$ 1,400

Equity Incentive Plans - Summ46

Equity Incentive Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Beginning balance (in shares)	2,295,393
Granted (in shares)	1,043,950
Exercised (in shares)	(38,332)
Canceled (in shares)	(201,838)
Ending balance (in shares)	3,099,173	2,295,393
Weighted Average Exercise Price
Beginning balance (USD per share)	$ 7.82
Granted (USD per share)	7.76
Exercised (USD per share)	5.95
Canceled (USD per share)	9.21
Ending balance (USD per share)	$ 7.74	$ 7.82
Stock Options, Additional Disclosures
Weighted average remaining contractual life, Outstanding	8 years 1 month 5 days	8 years 2 months 12 days
Total aggregate intrinsic value, Outstanding	$ 2,264	$ 6,774
Vested and expected to vest (in shares)	3,099,173
Weighted average exercise price of shares vested and expected to vest (USD per share)	$ 7.74
Weighted average remaining contractual life of shares vested and expected to vest (in years)	8 years 1 month 5 days
Total aggregate intrinsic value of shares vested and expected to vest	$ 2,264
Exercisable (in shares)	1,860,030
Weighted average exercise price of shares exercisable (USD per share)	$ 7.15
Weighted average remaining contractual life of shares exercisable (in years)	7 years 6 months 29 days
Total aggregate intrinsic value of shares exercisable	$ 2,205

Equity Incentive Plans - Summ47

Equity Incentive Plans - Summary of Black-Scholes Option Pricing Model Assumptions (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum (as a percentage)	1.05%	0.48%
Risk-free interest rate, maximum (as a percentage)	1.77%	1.08%
Expected dividend yield (as a percentage)	0.00%	0.00%
Expected volatility, minimum (as a percentage)	79.00%	80.00%
Expected volatility, maximum (as a percentage)	102.00%	107.00%
2015 Employee Stock Purchase Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	6 months
2015 Employee Stock Purchase Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	2 years	2 years
Authorized for future stock awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum (as a percentage)	1.87%	1.14%
Risk-free interest rate, maximum (as a percentage)	2.23%	2.09%
Expected dividend yield (as a percentage)	0.00%	0.00%
Expected volatility, minimum (as a percentage)	79.00%	80.00%
Expected volatility, maximum (as a percentage)	86.00%	82.00%
Authorized for future stock awards | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months
Authorized for future stock awards | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 12 days	6 years 1 month 12 days

Equity Incentive Plans - Summ48

Equity Incentive Plans - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,714	$ 4,344
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,428	2,005
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 3,286	$ 2,339

Significant Agreements and Co49

Significant Agreements and Contracts (Details) - Subaward Agreement - CD201 product candidate - USD ($) $ in Millions	Mar. 30, 2017	Dec. 31, 2017
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Qualifying development expenses to be reimbursed by CARB-X upon acceptance of new initial drug application	$ 3.9
Qualifying development expenses to be reimbursed through a Phase 1 clinical trial of CD201	$ 3
Reduction in research and development expense		$ 0.5
Billed accounts receivable		0.1
Unbilled accounts receivable		$ 0.2
Agreement termination, written notice period	30 days

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Effective income tax reconciliation at federal statutory rate (as a percent)	34.00%	34.00%	34.00%
Deferred tax assets, valuation allowance	$ 38,583	$ 33,451
Provisional income tax expense due to The Tax Cuts and Jobs Act	17,300
Unrecognized tax benefits	10,756	$ 4,642	$ 356	$ 108
Unrecognized tax benefits that would impact on effective tax rate	8,600
Federal
Income Tax Contingency [Line Items]
Net operating loss carryforwards	122,500
Tax credit carryforwards, research and development	12,500
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards	81,500
Tax credit carryforwards, research and development	$ 1,600

Income Taxes - Reconciliation B

Income Taxes - Reconciliation Between Income Taxes Computed at Federal Statutory Rate and Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal income taxes at 34%	$ (18,947)	$ (16,334)	$ (10,946)
State income tax, net of federal benefit	0	(1)	(1,821)
Tax effect on nondeductible expenses	3,389	1,650	341
Research credits	(8,125)	(3,538)	(676)
Rate change	0	267	0
Change in valuation allowance	5,133	14,996	13,084
Reserve for uncertain tax positions	1,451	2,883	0
Tax Cuts and Jobs Act	17,334	0	0
Other	(235)	77	18
Income tax expense	$ 0	$ 0	$ 0

Income Taxes - Significant Comp

Income Taxes - Significant Components of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating losses	$ 26,364	$ 27,309
Research credits	10,232	3,646
Intangibles	265	466
Other	1,722	2,030
Total deferred tax assets	38,583	33,451
Less valuation allowance	(38,583)	(33,451)
Income tax expense	$ 0	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrecognized tax benefits
Balance as of the beginning of the year	$ 4,642	$ 356	$ 108
Increases related to current year tax positions	3,965	921	248
Increases related to prior year tax positions	2,149	3,365	0
Balance as of the end of the year	$ 10,756	$ 4,642	$ 356

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)optionclaim1	Dec. 31, 2016USD ($)
Commitments and Contingencies Disclosure [Abstract]
Number of claims and actions pending | claim1	0
Number of operating lease options for extension | option	2
Operating leases renewal term (in years)	2 years
Annual increase in base rent (as a percent)	3.00%
Lease rent expense | $	$ 704	$ 733
Contractual obligation, contract termination notice period	30 days

Commitments and Contingencies55

Commitments and Contingencies - Schedule of Future Minimum Lease Payment (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 746
Total minimum lease payments	$ 746

Subsequent Events (Details)

Subsequent Events (Details) - Controlled equity sales agreement with Cantor Fitzgerald & Co - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Feb. 20, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Common stock sold (in shares)		240,178
Net proceeds		$ 1.8
Subsequent event
Subsequent Event [Line Items]
Common stock sold (in shares)	241,837
Net proceeds	$ 1.7

Selected Quarterly Financial 57

Selected Quarterly Financial Data (Unaudited) (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]
Operating expenses	$ 13,459	$ 12,249	$ 16,615	$ 13,398	$ 14,353	$ 12,336	$ 11,862	$ 9,885	$ 55,721	$ 48,436	$ 32,313
Other income (expense)	31	(8)	(30)	0	(41)	109	107	96
Net loss	$ (13,428)	$ (12,257)	$ (16,645)	$ (13,398)	$ (14,394)	$ (12,227)	$ (11,755)	$ (9,789)	$ (55,728)	$ (48,165)	$ (32,193)
Basic and diluted net loss per share (USD per share)	$ (0.69)	$ (0.73)	$ (0.99)	$ (0.80)	$ (0.88)	$ (0.88)	$ (0.85)	$ (0.71)	$ (3.18)	$ (3.32)	$ (3.25)
Shares used to compute basic and diluted net loss per share (in shares)	19,489,375	16,864,211	16,831,960	16,795,366	16,352,046	13,910,145	13,871,938	13,807,825	17,500,853	14,488,987	9,920,382