Cidara Therapeutics (CDTX) 10-K 28 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 20, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
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 Emerging Growth Company	true
Entity Small Business	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		27,816,014
Entity Public Float			$ 139.5

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 74,562	$ 60,813
Short-term investments	0	14,501
Accounts receivable	0	321
Prepaid expenses and other current assets	2,567	2,035
Total current assets	77,129	77,670
Property and equipment, net	712	1,044
Other assets	1,271	321
Total assets	79,112	79,035
Current liabilities:
Accounts payable	2,846	2,590
Accrued liabilities	3,883	4,257
Accrued compensation and benefits	2,824	2,571
Contingent forward purchase obligation	411	0
Current portion of term loan	9,928	2,667
Total current liabilities	19,892	12,085
Term loan, less debt issuance costs	0	7,206
Other long-term liabilities	81	0
Total liabilities	19,973	19,291
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized at December 31, 2018 and December 31, 2017:	0	0
Common stock, $0.0001 par value; 200,000,000 shares authorized at December 31, 2018 and 2017; 27,816,014 shares issued and outstanding at December 31, 2018; 20,534,993 and 20,525,688 shares issued and outstanding, respectively, at December 31, 2017	3	2
Additional paid-in capital	277,871	209,140
Accumulated other comprehensive loss	0	(8)
Accumulated deficit	(218,735)	(149,390)
Total stockholders' equity	59,139	59,744
Total liabilities and stockholders' equity	79,112	79,035
Series X Convertible Preferred Stock
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized at December 31, 2018 and December 31, 2017:	0	0
Total stockholders' equity	$ 0	$ 0

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
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 outstanding (in shares)	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)	27,816,014	20,534,993
Common stock, shares outstanding (in shares)	27,816,014	20,525,688
Series X Convertible Preferred Stock
Preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	5,000,000	0
Preferred stock, shares issued (in shares)	445,231	0
Preferred stock, shares outstanding (in shares)	445,231	0

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 49,142	$ 42,823	$ 35,699
General and administrative	14,143	12,898	12,737
Total operating expenses	63,285	55,721	48,436
Loss from operations	(63,285)	(55,721)	(48,436)
Other income (expense):
Change in fair value of contingent forward purchase obligation	3,851	0	0
Interest income (expense), net	629	(7)	271
Other expense	(211)	0	0
Total other income (expense)	4,269	(7)	271
Net loss	(59,016)	(55,728)	(48,165)
Recognition of beneficial conversion feature	(10,329)	0	0
Net loss attributable to common shareholders	$ (69,345)	$ (55,728)	$ (48,165)
Basic and diluted net loss per common share (USD per share)	$ (2.76)	$ (3.18)	$ (3.32)
Shares used to compute basic and diluted net loss per common share (in shares)	25,142,976	17,500,853	14,488,987
Net loss	$ (59,016)	$ (55,728)	$ (48,165)
Unrealized gain(loss) on short-term investments	8	(7)	7
Comprehensive loss	$ (59,008)	$ (55,735)	$ (48,158)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series X Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Other Comprehensive Loss	Registered direct offering	Registered direct offeringSeries X Convertible Preferred Stock	Registered direct offeringCommon Stock	Registered direct offeringAdditional Paid-In Capital
Balance, beginning (in shares) at Dec. 31, 2015		0	13,786,285
Balance, beginning at Dec. 31, 2015	$ 103,912	$ 0	$ 1	$ 149,416	$ (45,497)	$ (8)
Issuance of stock (in shares)			2,752,637
Issuance of stock	26,622		$ 1	26,621
Issuance of common stock for exercise of stock options	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 common stock under Employee Stock Purchase Plan	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	16,771,314
Balance, ending at Dec. 31, 2016	88,179	$ 0	$ 2	181,840	(93,662)	(1)
Issuance of stock (in shares)			3,600,178
Issuance of stock	20,771		$ 0	20,771
Issuance of common stock for exercise of stock options	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
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 common stock under Employee Stock Purchase Plan	0
Unrealized (gain) loss on marketable securities	(7)					(7)
Net loss	(55,728)				(55,728)
Balance, ending (in shares) at Dec. 31, 2017		0	20,525,688
Balance, ending at Dec. 31, 2017	59,744	$ 0	$ 2	209,140	(149,390)	(8)
Issuance of stock (in shares)			847,937					445,231	6,185,987
Issuance of stock	6,440			6,440			$ 45,458		$ 1	$ 45,457
Beneficial conversion feature of Series X Convertible Preferred Stock	0			10,329	(10,329)
Issuance of common stock for exercise of stock options	5,710			5,710
Vesting of restricted shares (in shares)			9,305
Vesting of restricted shares	$ 21			21
Issuance of common stock for exercise of stock options (in shares)	89,031		89,031
Issuance of common stock for exercise of stock options	$ 204			204
Issuance of common stock under Employee Stock Purchase Plan (in shares)			158,066
Issuance of common stock under Employee Stock Purchase Plan	570			570
Issuance of common stock under Employee Stock Purchase Plan	0
Unrealized (gain) loss on marketable securities	8					8
Net loss	(59,016)				(59,016)
Balance, ending (in shares) at Dec. 31, 2018		445,231	27,816,014
Balance, ending at Dec. 31, 2018	$ 59,139	$ 0	$ 3	$ 277,871	$ (218,735)	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net loss	$ (59,016)	$ (55,728)	$ (48,165)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	523	667	732
Stock-based compensation	5,710	5,714	4,344
Non-cash interest expense	43	61	17
Amortization of discount or premium on short-term investments	31	(33)	(176)
Amortization of debt issue costs	13	18	5
Deferred rent	30	(29)	(8)
Change in fair value of contingent forward purchase obligations	(3,851)	0	0
Contingent forward purchase obligation offering costs	211	0	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(211)	(1,481)	(76)
Accounts payable and accrued liabilities	(59)	642	1,913
Accrued compensation	822	453	1,760
Other assets	(951)	(193)	(117)
Net cash used in operating activities	(56,705)	(49,909)	(39,771)
Investing activities:
Purchases of short-term investments	(14,548)	(19,523)	(69,617)
Maturities of short-term investments	29,026	24,300	95,500
Purchases of property and equipment	(177)	(306)	(401)
Net cash provided by investing activities	14,301	4,471	25,482
Financing activities:
Proceeds from Registered Direct Offering, net of offering costs	49,509	0	0
Proceeds from issuance of common stock, net of offering costs	6,440	20,735	26,622
Proceeds from issuance of Term Loan, net of offering costs	0	0	9,947
Proceeds from exercise of stock options	204	228	525
Repurchase of unvested restricted stock	0	(79)	0
Net cash provided by financing activities	56,153	20,884	37,094
Net increase (decrease) in cash and cash equivalents	13,749	(24,554)	22,805
Cash and cash equivalents at beginning of year	60,813	85,367	62,562
Cash and cash equivalents at end of year	74,562	60,813	85,367
Supplemental disclosure of cash flows:
Interest paid	582	511	0
Non-cash investing activity:
Property and equipment acquired but not yet paid	14	30	21
Non-cash financing activities:
Issuance of warrants to purchase common stock upon execution of term loan	0	0	175
Vesting of early exercised stock options	21	44	197
Purchase of shares pursuant to Employee Stock Purchase Plan	570	543	562
Receivable for issuance of common stock, net of offering costs	$ 0	$ 36	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
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 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 “Tax Act”), which among other provisions, reduced the U.S. corporate tax rate from 35% to 21%, effective January 1, 2018. Due to the timing of the enactment and the complexity involved in applying the provisions of the Tax Act, the Company made reasonable estimates of the effects and recorded provisional amounts, offset with valuation allowances, in its financial statements as of December 31, 2017. At December 31, 2018, the Company has completed its assessment of the impact of the Tax Cuts and Jobs Act and has reflected the impact in the current year. At December 31, 2018, there were no material changes from the provisional amounts recorded for the year ended December 31, 2017. Revenue Recognition —The Company recognizes revenues when customers obtain control of promised goods or services, in an amount that reflects the consideration which it expects to receive in exchange for those goods or services. The Company recognizes revenues following the five step model prescribed under Accounting Standards Update ("ASU") No. 2014-09 ("ASU 2014-09"): (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenues when (or as) the Company satisfies the performance obligation. Grant Funding —The Company has received research and development funding through a grant from CARB-X, a public-private partnership focused on antibacterials. The Company has also been awarded a partnership grant with Rutgers University from the NIAID. The Company has evaluated the terms of the grants 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 nonclinical and clinical trial costs. The Company accrues nonclinical 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 short-term investments. Comprehensive 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. The Company recognizes forfeitures related to stock-based compensation as they occur. Net Loss Per Share —Basic net loss per share is calculated by dividing the net loss allocable to common shares 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 allocable to common shares 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 warrants, Series X Convertible Preferred stock, unvested restricted common stock subject to repurchase, and RSUs and options outstanding under the Company’s stock option plans. 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, 2018 2017 Common stock warrants 12,517,328 17,331 Series X Convertible Preferred stock 4,452,310 — Common stock options, RSUs and PRSUs issued and outstanding 4,392,671 3,099,173 Common stock subject to repurchase — 9,305 Total 21,362,309 3,125,809 Fair Value of Financial Instruments — The Company follows ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance 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, contingent forward purchase obligations, 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 fair value of contingent forward purchase obligations is based on a probability-weighted valuation approach (See Note 4). The Company believes that the fair value of long-term debt approximates its carrying value. Recently Issued Accounting Standards — During 2016, the FASB issued ASU 2016-02, “Leases,” 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 2018, the FASB issued ASU 2018-07, "Improvements to Nonemployee Share-Based Payment Accounting," which expanded the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from non-employees. Under the ASU, the guidance on such payments to nonemployees is aligned with the accounting for share-based payments granted to employees, including the measurement of equity-classified awards, which is fixed at the grant date under the new guidance. The updated guidance is effective for interim and annual periods beginning after December 15, 2018, and early adoption is permitted. The Company is currently assessing the impact that this standard will have on its consolidated financial statements. During 2018, the FASB issued ASU 2018-13, "Changes to the Disclosure Requirements for Fair Value Measurement," which modifies certain disclosure requirements on fair value measurements. The updated guidance is effective for interim and annual periods beginning after December 15, 2019, and early adoption is permitted. The Company is currently assessing the impact that this standard will have on its consolidated financial statements.

The Company and Basis of Presen

The Company and Basis of Presentation	12 Months Ended
	Dec. 31, 2018
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. The Company’s portfolio is comprised of a proprietary product candidate for the treatment and prevention of serious fungal infections. The Company is also conducting research in bacterial and viral infection. T he Company formed wholly-owned subsidiaries, Cidara Therapeutics UK Limited, in England, and Cidara Therapeutics (Ireland) Limited, in Ireland, in March 2016 and October 2018, respectively, 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 Company has experienced net losses and negative cash flows from operating activities since its inception. At December 31, 2018 , the Company had an accumulated deficit of $218.7 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. At December 31, 2018, the Company had cash and cash equivalents of $74.6 million . Based on the Company’s current business plan, management believes that existing cash and cash equivalents will be sufficient to fund the Company’s obligations through the third quarter of 2019. The Company’s ability to execute its operating plan beyond the third quarter of 2019 depends on its ability to obtain additional funding through equity offerings, debt financings or potential licensing and collaboration arrangements. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business. However, the Company’s current working capital, anticipated operating expenses and net losses and the uncertainties surrounding its ability to raise additional capital as needed, as discussed below, raise substantial doubt about its ability to continue as a going concern for a period of one year following the date that these financial statements are issued. The consolidated financial statements do not include any adjustments for the recovery and classification of assets or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company plans to continue to fund its losses from operations through cash and cash equivalents on hand, as well as through future equity offerings, debt financings, other third party funding, and potential licensing or collaboration arrangements. There can be no assurance that additional funds will be available when needed from any source or, if available, will be available on terms that are acceptable to the Company. Even if the Company raises additional capital, it may also be required to modify, delay or abandon some of its plans which could have a material adverse effect on the Company’s business, operating results and financial condition and the Company’s ability to achieve its intended business objectives. Any of these actions could materially harm the Company’s business, results of operations and future prospects. Basis of Consolidation —The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. 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 stock options, the fair value of the Company's contingent forward purchase obligations, and certain accruals, including those related to nonclinical 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.

Short-Term Investments

Short-Term Investments	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Short-Term Investments	SHORT-TERM INVESTMENTS The Company did not have any available-for-sale securities at December 31, 2018 . The following table summarizes the available-for-sale securities held at 2017 (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 All available-for-sale securities held at December 31, 2017 had maturities of less than one year. Unrealized gains and losses on available-for-sale securities are included as a component of other comprehensive loss. 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. During the years ended December 31, 2018 and 2017 , the Company did not recognize any impairment or gains or losses on sales of available-for-sale securities.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
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. The carrying amounts of accounts payable and accrued liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments. Based on the borrowing rates available to the Company for loans with similar terms, which is considered a Level 2 input as described below, the Company believes that the fair value of long-term debt approximates its carrying value. 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 for 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. As discussed in Note 7, on May 21, 2018, the Company entered into a subscription agreement with certain investors providing for the purchase and sale of up to an aggregate of $120.0 million of its common stock and preferred stock in three closings. The second and optional third closings and warrants related to the optional third closing, which are triggered by the Company's announcement of topline data of Part B of its STRIVE Phase 2 clinical trial of rezafungin, contain features for subsequent closings that are not solely within the control of the Company and that embody an obligation that the Company must settle by issuing a variable number of shares when the obligation is based predominantly on having a fixed value at inception. In accordance with ASC 480, "Distinguishing Liabilities from Equity," the Company determined that these closings are classified as liabilities and represent contingent forward purchase obligations. These liabilities are required to be recorded at their estimated fair value initially and on a recurring basis. The contingent forward purchase obligations are classified within Level 3 of the fair value hierarchy as the Company is using a probability-weighted valuation approach, utilizing significant unobservable inputs including the probability and estimated timing of achieving positive or negative results associated with Part B of the STRIVE Phase 2 clinical trial and estimated discount rates related to the risk of achievement of the expected equity issuances. The liability was initially recorded at $4.3 million on May 21, 2018 and fair value adjustments resulting in a gain of $3.9 million were recorded during the year ended December 31, 2018 . The liability was valued at $0.4 million for the year ended December 31, 2018 . 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, 2018 Assets: Money market funds $ 74,077 $ 74,077 $ — $ — Total assets at fair value $ 74,077 $ 74,077 $ — $ — Liabilities: Contingent forward purchase obligations $ 411 $ — $ — $ 411 Total liabilities at fair value $ 411 $ — $ — $ 411 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 $ —

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment	PROPERTY AND EQUIPMENT Property and equipment consisted of the following (in thousands): December 31, 2018 2017 Laboratory equipment $ 2,114 $ 2,051 Leasehold improvements 425 425 Computer hardware and software 455 327 Office equipment 119 119 Furniture and fixtures 142 142 3,255 3,064 Less accumulated depreciation and amortization (2,543 ) (2,020 ) Total $ 712 $ 1,044 Depreciation and amortization of property and equipment of $523,000 and $667,000 were recorded for the years ended December 31, 2018 and 2017 , respectively.

Debt

Debt	12 Months Ended
	Dec. 31, 2018
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, because the Company achieved positive clinical results from the STRIVE Phase 2 clinical trial of rezafungin by March 31, 2018, the Company could, 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 the Term A Loan, the "Term Loans"). The Company did not borrow any funds available under the Term B Loan before the draw period ended. 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 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. 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. 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. On June 13, 2018, the Company and the Lender entered into a First Amendment to the Loan Agreement, which reset the operating covenant to require the Company to achieve positive data from Part B of the STRIVE Phase 2 clinical trial of rezafungin on or prior to July 31, 2019 (the "Milestone"). On July 27, 2018, the Company and the Lender entered into a Second Amendment to the Loan Agreement, which amended, among other things, the interest-only period, the date of maturity (the "Maturity Date") and the interest rate. The Maturity Date is January 3, 2022. Payments under the Term Loans will be interest-only through July 31, 2019, which will be extended to October 31, 2019 if the Milestone is achieved. The interest-only period will be followed by equal monthly payments of principal and interest. 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 0.75% . At December 31, 2018 , the Term Loans bear interest at 6.25% . The Company evaluated the First and Second Amendments to evaluate whether the amendments represented modifications or extinguishment of debt. The Company determined that the amendments did not represent a substantial change from the original Loan Agreement and accounted for the amendments as debt modifications. Costs previously deferred under the original terms of the Loan Agreement are amortized into interest expense over the new term of the Second Amendment. 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 data from Part B of the STRIVE Phase 2 clinical trial of rezafungin on or prior to July 31, 2019, 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. The principal payments due under the Loan Agreement have been classified as a current liability at December 31, 2018 due to the considerations discussed in Note 1 and the assessment that the material adverse change clause under the Loan Agreement is not within the Company's control. The Company has not been notified of an event of default by the Lenders as of the date of the filing of this Form 10-K. As of December 31, 2018 , future principal payments due under the Term A Loan are as follows (in thousands): Year ended: December 31, 2019 $ 1,667 December 31, 2020 4,000 December 31, 2021 4,000 December 31, 2022 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 $56,000 and $78,000 for the years ended December 31, 2018 and 2017 , respectively, for the amortization of the fair value of the warrants and debt issue costs .

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	STOCKHOLDERS’ EQUITY May 2018 Registered Direct Offering — On May 21, 2018, the Company entered into a subscription agreement with certain investors providing for the purchase and sale, in a registered direct offering, of up to an aggregate of $120.0 million of its common stock and preferred stock in three closings. On May 23, 2018, the Company completed the first closing, which was comprised of 6,185,987 shares of common stock at an offering price of $4.70 per share, 445,231 shares of Series X Convertible Preferred Stock at an offering price of $47.00 per share, and an option fee relating to the third closing paid by the investors for a total of $0.5 million . In a private placement concurrent with the first closing (the “First Private Placement”), the Company also sold warrants, at $0.125 per warrant share, to purchase an aggregate of 12,499,997 shares of common stock. Net proceeds for the first closing and the First Private Placement were $49.5 million . The Company performed an analysis to allocate the proceeds from the May 2018 registered direct offering to the offering's various components on a relative fair value basis, including the contingent forward purchase obligations (discussed further in Note 4) as well as the common stock, Series X Convertible Preferred Stock, warrants, and option fee. With respect to the Series X Convertible Preferred Stock, because the adjusted conversion price on the commitment date (following the allocation of proceeds on a fair value basis) was below the fair value of the common stock at the date of issuance, a beneficial conversion feature with a calculated fair value of $10.3 million existed at the issuance date. The beneficial conversion feature is amortized as a deemed dividend to the preferred holders. As the Series X Convertible Preferred Stock is fully convertible at issuance, the full amortization of the $10.3 million was recorded at issuance as a one-time deemed dividend on May 23, 2018. This one-time, non-cash deemed dividend impacted net loss attributable to common stockholders and net loss attributable to common stockholders per share for the year ended December 31, 2018 . In the second closing of the offering, the Company may sell up to an additional $50.0 million in shares of common stock to investors who purchased at least $1.0 million of shares of common stock in the first closing of the offering at a purchase price per share that is equal to 75% of the volume weighted average price of the common stock for the five trading days following the Company’s public release of topline data from Part B of its STRIVE global, randomized Phase 2 clinical trial of rezafungin, provided that the Company will not be obligated to complete the second closing of the offering if the purchase price is less than $4.70 per share. In the optional third closing, which would be held five trading days following the second closing, purchasers who fully participate in the second closing may, at their option, purchase up to an additional $20.0 million of common stock at a purchase price per share equal to the purchase price of the shares purchased at the second closing. At the Company’s option, and prior to the completion of the second or third closing, as applicable, the Company may reduce the aggregate offering size of the such closing by the dollar amount received by the Company from any (i) strategic partnership or other non-dilutive source of funding or (ii) sale of equity securities at a price greater than $6.81 per share. If the volume weighted average price of the Company's common stock for the five trading days following the Company's public release of topline data from Part B of its STRIVE global, randomized Phase 2 clinical trial of rezafungin is below $6.27 , the resulting purchase price for the second and third closings will be less than $4.70 per share and the Company will be unable to complete the second and third closings without first obtaining the approval of our stockholders. As of the date the Company issued financial statements for the fiscal year ending December 31, 2018 , the price of the Company's common stock was below $6.27 . The Company will also offer to each purchaser in the second or third closing the opportunity, in lieu of purchasing common stock, to purchase Series X Convertible Preferred Stock. For each share of Series X Convertible Preferred Stock purchased in the offering in lieu of common stock, the Company will reduce the number of shares of common stock being sold by 10 shares. Each share of Series X Convertible Preferred Stock is convertible into 10 shares of common stock. As the issuance of the additional closings are outside the control of the Company, the second closing and optional third closing are accounted for as a liability in accordance with ASC 480, Distinguishing Liabilities from Equity , which is measured at fair value on a recurring basis. See Note 4 to our financial statements for additional information. In a private placement to be held concurrently with the optional third closing (the “Second Private Placement”), the Company would sell warrants to purchase up to 2,500,000 shares of Common Stock to the purchasers that participate, at a purchase price of $0.125 per warrant share (such warrants, together with the warrants sold in the First Private Placement, each, a “Warrant”, and collectively, the “Warrants”). The Warrants are exercisable immediately for cash at an exercise price of $6.81 per share. The Warrants issued in the First Private Placement will expire upon the earliest of (i) five years from the date of the first closing of the offering, (ii) the date that the holder of such Warrant transfers or sells any of the shares of Common Stock purchased by such holder in the first closing of the offering, if such transfer or sale occurs prior to the date that is 120 calendar days following the closing of the first closing of the offering, (iii) the taking of any short position on the Common Stock by the holder of such Warrant prior to the completion of the second closing of the offering, and (iv) the failure by the holder of such Warrant to purchase its pro rata allocation of shares of Common Stock in the second closing of the offering. The Company accounts for the Warrants as equity instruments in accordance with ASC 480, Distinguishing Liabilities from Equity . The Warrants issued in the Second Private Placement will expire five years from the date of the third closing of the offering. 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 at December 31, 2018 . In May 2018, the Company designated 5,000,000 shares of preferred stock as Series X Convertible Preferred Stock with a par value of $0.0001 per share. As of December 31, 2018 , 445,231 shares of Series X Convertible Preferred Stock were issued and outstanding. The specific terms of the Series X Convertible Preferred Stock are as follows: Conversion: Each share of Series X Convertible Preferred Stock is convertible at the option of the holder into 10 shares of common stock. Holders are not permitted to convert Series X Convertible Preferred Stock into common stock if, after conversion, the holder, its affiliates, and any other person whose beneficial ownership of common stock would be aggregated with the holder's for purposes of Section 13(d) or Section 16 of the Exchange Act, would beneficially own more than 9.99% of the number of shares of common stock outstanding immediately after the conversion. Dividends: Holders of Series X Convertible Preferred Stock are not entitled to receive any dividends except to the extent that dividends are paid on the Company's common stock. If dividends are paid on shares of common stock, holders of Series X Convertible Preferred Stock are entitled to participate in such dividends on an as-converted basis. Liquidation: Upon the liquidation, dissolution, or winding up of the company, each holder of Series X Convertible Preferred Stock will participate pari passu with any distribution of proceeds to holders of common stock. Voting: Shares of Series X Convertible Preferred Stock will generally have no voting rights, except as required by law and except that the consent of the holders of a majority of the outstanding Series X Convertible Preferred Stock will be required to amend the terms of the Series X Convertible Preferred Stock , if such action would adversely alter or change the preferences, rights, privileges or powers of, or restrictions provided for the benefit of the Series X Convertible Preferred Stock, or to increase or decrease (other than by conversion) the number of authorized shares of Series X Convertible Preferred Stock. The Company evaluated the Series X Convertible Preferred Stock for liability or equity classification under ASC 480, Distinguishing Liabilities from Equity , and determined that equity treatment was appropriate because the Series X Convertible Preferred Stock did not meet the definition of the liability instruments defined thereunder as convertible instruments. Specifically, the Series X Convertible Preferred Stock does not meet the criteria for classification as an ASC 480 liability. As such, the Series X Convertible Preferred Stock should be recorded as permanent equity. Additionally, the Series X Convertible Preferred Stock is not redeemable for cash or other assets (i) on a fixed or determinable date, (ii) at the option of the holder, and (iii) upon the occurrence of an event that is not solely within control of the Company. Common Stock —The Company had 200,000,000 shares of common stock authorized as of December 31, 2018 . 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 years ended December 31, 2018 and December 31, 2017 , the Company sold 847,937 and 240,178 shares of common stock for net proceeds of approximately $6.4 million and $1.8 million , respectively, 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, 2018 2017 Common stock warrants 12,517,328 17,331 Series X Convertible Preferred stock 4,452,310 — Stock options, RSUs and PRSUs issued and outstanding 4,392,671 3,099,173 Authorized for future stock awards 669,873 1,006,307 Awards available under the ESPP 706,242 380,875 Total 22,738,424 4,503,686

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2018
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, 2018 , 158,066 shares were issued pursuant to the ESPP. Restricted Stock The Company permits exercise of certain stock options prior to vesting. Any such exercised shares are restricted and subject to repurchase by the Company until the conditions for vesting are met. At December 31, 2018 there was no liability for cash received from the early exercise of stock options. At December 31, 2017 , the liabilities for the cash received from the early exercise of stock options was $21,000 and was 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, 2018 , there were no shares subject to repurchase by the Company. Restricted Stock Units The following table summarizes RSU and PRSU activity during the year ended December 31, 2018 : Number of Outstanding at December 31, 2017 227,500 RSUs and PRSUs granted 55,000 RSUs and PRSUs vested (2,500 ) RSUs and PRSUs canceled (20,000 ) Outstanding at December 31, 2018 260,000 For the year ended December 31, 2018 , stock-based compensation expense related to RSUs and PRSUs was approximately $0.3 million . At December 31, 2018 , estimated unrecognized compensation expense related to RSUs and PRSUs granted to employees was approximately $1.0 million . Stock Options The following table summarizes stock option activity during the year ended December 31, 2018 : Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Life in Years Total Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2017 3,099,173 $ 7.74 8.10 $ 2,264 Options granted 1,436,250 4.22 Options exercised (89,031 ) 2.29 Options canceled (313,721 ) 8.41 Outstanding at December 31, 2018 4,132,671 $ 6.58 7.41 $ 25 Vested and expected to vest at December 31, 2018 4,132,671 $ 6.58 7.41 $ 25 Exercisable at December 31, 2018 2,423,061 $ 7.29 6.74 $ 25 The intrinsic value of a stock option is the difference between the market price of the common stock at the measurement date and the exercise price of the option. 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, 2018 2017 2015 EIP Risk-free interest rate 2.55% - 3.06% 1.87% - 2.23% Expected dividend yield 0% 0% Expected volatility 83% 79% - 86% Expected term (years) 5.50 - 6.08 5.50 - 6.08 2015 ESPP Risk-free interest rate 2.14% - 2.81% 1.05% - 1.77% Expected dividend yield 0% 0% Expected volatility 77% - 92% 79% - 102% 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, 2018 2017 Research and development $ 2,676 $ 2,428 General and administrative 3,034 3,286 Total $ 5,710 $ 5,714 The weighted-average grant date fair value of stock options granted to employees during the year ended December 31, 2018 was $2.98 per share. The total grant date fair value of stock options that vested during the year ended December 31, 2018 was $3.6 million . As of December 31, 2018 , total unrecognized share-based compensation expense related to unvested employee stock options of the Company was approximately $5.4 million . This unrecognized compensation cost is expected to be recognized over a weighted-average period of approximately 2.31 years. As of December 31, 2018 , total unrecognized compensation expense related to the Company’s ESPP was approximately $0.8 million . This unrecognized compensation cost is expected to be recognized over approximately 0.70 years. Common Stock Warrants A summary of warrant activity for the year ended December 31, 2018 is presented below: Warrants Weighted Average Exercise Price Total Intrinsic Value Outstanding at December 31, 2017 17,331 11.54 $ — Issued 12,499,997 6.81 — Exercised — — — Canceled — — — Outstanding at December 31, 2018 12,517,328 6.82 $ — The intrinsic value of a common stock warrant is the difference between the market price of the common stock at the measurement date and the exercise price of the warrant.

Significant Agreements and Cont

Significant Agreements and Contracts	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [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), the 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 was intended to support 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, 2018 , the Company did not recognize any reductions to research and development expenses for costs eligible for reimbursement under the Subaward Agreement. As of December 31, 2018 , there were no billed or unbilled accounts receivable 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. The Company will no longer be seeking funding under the Subaward Agreement relating to CD201. Partnership Grant for the Development of Cloudbreak Antibody-Drug Conjugates In May 2018, the Company and Rutgers University were awarded a five year, $5.5 million partnership grant from the NIAID. The grant will fund continued research and development of the Company's Cloudbreak platform to identify novel immunotherapy agents for the treatment and prevention of serious and life-threatening viral infections and multi-drug resistant Gram-negative bacterial infections in high-risk populations. The Company began work under this grant in July 2018 but has not billed Rutgers University for any work performed to date, nor recognized any potential reimbursements in the statement of operations for the year ended December 31, 2018 as the subaward agreement between the Company and Rutgers University has not yet been executed.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
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 and the provision for income taxes (in thousands): Years Ended December 31, 2018 2017 2016 Federal income taxes at 21% for 2018 and 34% for 2017 and 2016 $ (12,393 ) $ (18,947 ) $ (16,334 ) State income tax, net of federal benefit — — (1 ) Tax effect on nondeductible expenses (278 ) 3,389 1,650 Research credits (4,737 ) (8,125 ) (3,538 ) Rate change — — 267 Change in valuation allowance 16,421 5,133 14,996 Reserve for uncertain tax positions 1,184 1,451 2,883 Tax Cuts and Jobs Act — 17,334 — Other (197 ) (235 ) 77 Income tax expense $ — $ — $ — Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2018 2017 Deferred tax assets: Net operating losses $ 38,268 $ 26,364 Research credits 14,007 10,232 Intangibles 241 265 Other 2,488 1,722 Total deferred tax assets 55,004 38,583 Less valuation allowance (55,004 ) (38,583 ) Income tax expense $ — $ — At December 31, 2018 , the Company had federal and state net operating loss carryforwards of approximately $179.1 million and $132 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 $17 million and state research and development credit carryforwards totaling $2.4 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 2029. 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 $55.0 million and $38.6 million as of December 31, 2018 and 2017 , 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 made a reasonable estimate of the effects on their existing deferred tax balances. At December 31, 2017 the Company recognized a provisional amount of $17.3 million which was included as a component of income tax expense from continuing operations offset with valuation allowances. As of December 31, 2018, the Company has completed its assessment of the impact of the Tax Cuts and Jobs Act with no additional impact recorded in the current year. 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, 2018 and 2017 , the unrecognized tax benefits recorded were approximately $16.5 million and $10.8 million , respectively. Approximately $13.4 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 2018 , 2017 and 2016 is as follows (in thousands): Years Ended December 31, 2018 2017 2016 Balance as of the beginning of the year $ 10,756 $ 4,642 $ 356 Increases related to current year tax positions 1,224 2,149 921 Increases related to prior year tax positions 4,544 3,965 3,365 Balance as of the end of the year $ 16,524 $ 10,756 $ 4,642 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, 2018
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, 2018 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. On June 29, 2018 the Company entered into a Fourth Amendment to its lease which extended the term of the lease by an additional 36 months and increases base rent to $70,000 per month effective January 1, 2019. The Company has also been granted an option, exercisable prior to September 30, 2019, to expand its leased premises on the same terms as the current lease, subject to compliance with specified conditions. The lease expires in December 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 January. 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, 2018 are summarized as follows (in thousands): 2019 836 2020 861 2021 887 Total minimum lease payments $ 2,584 Rent expense was $776,000 and $704,000 for the years ended December 31, 2018 and 2017 , 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.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter 2018 Operating expenses $ 16,810 $ 15,152 $ 14,725 $ 16,598 Other income (expense) 61 (1,154 ) 1,106 4,256 Net loss (16,749 ) (16,306 ) (13,619 ) (12,342 ) Basic and diluted net loss per share $ (0.80 ) $ (1.13 ) $ (0.49 ) $ (0.44 ) Shares used to compute basic and diluted net loss per share 20,894,353 23,592,763 27,705,472 27,780,212 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

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
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 Company has experienced net losses and negative cash flows from operating activities since its inception. At December 31, 2018 , the Company had an accumulated deficit of $218.7 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.
Basis of Consolidation	Basis of Consolidation —The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. 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 stock options, the fair value of the Company's contingent forward purchase obligations, and certain accruals, including those related to nonclinical 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 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 “Tax Act”), which among other provisions, reduced the U.S. corporate tax rate from 35% to 21%, effective January 1, 2018. Due to the timing of the enactment and the complexity involved in applying the provisions of the Tax Act, the Company made reasonable estimates of the effects and recorded provisional amounts, offset with valuation allowances, in its financial statements as of December 31, 2017. At December 31, 2018, the Company has completed its assessment of the impact of the Tax Cuts and Jobs Act and has reflected the impact in the current year. At December 31, 2018, there were no material changes from the provisional amounts recorded for the year ended December 31, 2017.
Revenue Recognition	Revenue Recognition —The Company recognizes revenues when customers obtain control of promised goods or services, in an amount that reflects the consideration which it expects to receive in exchange for those goods or services. The Company recognizes revenues following the five step model prescribed under Accounting Standards Update ("ASU") No. 2014-09 ("ASU 2014-09"): (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenues when (or as) the Company satisfies the performance obligation. 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.
Grant Funding and Research and Development Costs	Grant Funding —The Company has received research and development funding through a grant from CARB-X, a public-private partnership focused on antibacterials. The Company has also been awarded a partnership grant with Rutgers University from the NIAID. The Company has evaluated the terms of the grants 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 nonclinical and clinical trial costs. The Company accrues nonclinical 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 short-term investments. Comprehensive 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. The Company recognizes forfeitures related to stock-based compensation as they occur.
Net Loss Per Share	Net Loss Per Share —Basic net loss per share is calculated by dividing the net loss allocable to common shares 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 allocable to common shares 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 warrants, Series X Convertible Preferred stock, unvested restricted common stock subject to repurchase, and RSUs and options outstanding under the Company’s stock option plans. 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 ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance 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, contingent forward purchase obligations, 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 fair value of contingent forward purchase obligations is based on a probability-weighted valuation approach (See Note 4). The Company believes that the fair value of long-term debt approximates its carrying value.
Recently Issued Accounting Standards	Recently Issued Accounting Standards — During 2016, the FASB issued ASU 2016-02, “Leases,” 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 2018, the FASB issued ASU 2018-07, "Improvements to Nonemployee Share-Based Payment Accounting," which expanded the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from non-employees. Under the ASU, the guidance on such payments to nonemployees is aligned with the accounting for share-based payments granted to employees, including the measurement of equity-classified awards, which is fixed at the grant date under the new guidance. The updated guidance is effective for interim and annual periods beginning after December 15, 2018, and early adoption is permitted. The Company is currently assessing the impact that this standard will have on its consolidated financial statements. During 2018, the FASB issued ASU 2018-13, "Changes to the Disclosure Requirements for Fair Value Measurement," which modifies certain disclosure requirements on fair value measurements. The updated guidance is effective for interim and annual periods beginning after December 15, 2019, and early adoption is permitted. The Company is currently assessing the impact that this standard will have on its consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 Common stock warrants 12,517,328 17,331 Series X Convertible Preferred stock 4,452,310 — Common stock options, RSUs and PRSUs issued and outstanding 4,392,671 3,099,173 Common stock subject to repurchase — 9,305 Total 21,362,309 3,125,809

Short-Term Investments (Tables)

Short-Term Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Securities	The Company did not have any available-for-sale securities at December 31, 2018 . The following table summarizes the available-for-sale securities held at 2017 (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

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 Assets: Money market funds $ 74,077 $ 74,077 $ — $ — Total assets at fair value $ 74,077 $ 74,077 $ — $ — Liabilities: Contingent forward purchase obligations $ 411 $ — $ — $ 411 Total liabilities at fair value $ 411 $ — $ — $ 411 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 $ —

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following (in thousands): December 31, 2018 2017 Laboratory equipment $ 2,114 $ 2,051 Leasehold improvements 425 425 Computer hardware and software 455 327 Office equipment 119 119 Furniture and fixtures 142 142 3,255 3,064 Less accumulated depreciation and amortization (2,543 ) (2,020 ) Total $ 712 $ 1,044

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Future Principal Payments Due	As of December 31, 2018 , future principal payments due under the Term A Loan are as follows (in thousands): Year ended: December 31, 2019 $ 1,667 December 31, 2020 4,000 December 31, 2021 4,000 December 31, 2022 333 Total future principal payments due under the Term A Loan $ 10,000

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance is as follows (in common stock equivalent shares): Years ended December 31, 2018 2017 Common stock warrants 12,517,328 17,331 Series X Convertible Preferred stock 4,452,310 — Stock options, RSUs and PRSUs issued and outstanding 4,392,671 3,099,173 Authorized for future stock awards 669,873 1,006,307 Awards available under the ESPP 706,242 380,875 Total 22,738,424 4,503,686

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 : Number of Outstanding at December 31, 2017 227,500 RSUs and PRSUs granted 55,000 RSUs and PRSUs vested (2,500 ) RSUs and PRSUs canceled (20,000 ) Outstanding at December 31, 2018 260,000
Schedule of Stock Option Activity	The following table summarizes stock option activity during the year ended December 31, 2018 : Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Life in Years Total Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2017 3,099,173 $ 7.74 8.10 $ 2,264 Options granted 1,436,250 4.22 Options exercised (89,031 ) 2.29 Options canceled (313,721 ) 8.41 Outstanding at December 31, 2018 4,132,671 $ 6.58 7.41 $ 25 Vested and expected to vest at December 31, 2018 4,132,671 $ 6.58 7.41 $ 25 Exercisable at December 31, 2018 2,423,061 $ 7.29 6.74 $ 25
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, 2018 2017 2015 EIP Risk-free interest rate 2.55% - 3.06% 1.87% - 2.23% Expected dividend yield 0% 0% Expected volatility 83% 79% - 86% Expected term (years) 5.50 - 6.08 5.50 - 6.08 2015 ESPP Risk-free interest rate 2.14% - 2.81% 1.05% - 1.77% Expected dividend yield 0% 0% Expected volatility 77% - 92% 79% - 102% 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, 2018 2017 Research and development $ 2,676 $ 2,428 General and administrative 3,034 3,286 Total $ 5,710 $ 5,714
Summary of Warrant Activity	A summary of warrant activity for the year ended December 31, 2018 is presented below: Warrants Weighted Average Exercise Price Total Intrinsic Value Outstanding at December 31, 2017 17,331 11.54 $ — Issued 12,499,997 6.81 — Exercised — — — Canceled — — — Outstanding at December 31, 2018 12,517,328 6.82 $ —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
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 and the provision for income taxes (in thousands): Years Ended December 31, 2018 2017 2016 Federal income taxes at 21% for 2018 and 34% for 2017 and 2016 $ (12,393 ) $ (18,947 ) $ (16,334 ) State income tax, net of federal benefit — — (1 ) Tax effect on nondeductible expenses (278 ) 3,389 1,650 Research credits (4,737 ) (8,125 ) (3,538 ) Rate change — — 267 Change in valuation allowance 16,421 5,133 14,996 Reserve for uncertain tax positions 1,184 1,451 2,883 Tax Cuts and Jobs Act — 17,334 — Other (197 ) (235 ) 77 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, 2018 2017 Deferred tax assets: Net operating losses $ 38,268 $ 26,364 Research credits 14,007 10,232 Intangibles 241 265 Other 2,488 1,722 Total deferred tax assets 55,004 38,583 Less valuation allowance (55,004 ) (38,583 ) 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 2018 , 2017 and 2016 is as follows (in thousands): Years Ended December 31, 2018 2017 2016 Balance as of the beginning of the year $ 10,756 $ 4,642 $ 356 Increases related to current year tax positions 1,224 2,149 921 Increases related to prior year tax positions 4,544 3,965 3,365 Balance as of the end of the year $ 16,524 $ 10,756 $ 4,642

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 are summarized as follows (in thousands): 2019 836 2020 861 2021 887 Total minimum lease payments $ 2,584

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Data (Unaudited)	First Quarter Second Quarter Third Quarter Fourth Quarter 2018 Operating expenses $ 16,810 $ 15,152 $ 14,725 $ 16,598 Other income (expense) 61 (1,154 ) 1,106 4,256 Net loss (16,749 ) (16,306 ) (13,619 ) (12,342 ) Basic and diluted net loss per share $ (0.80 ) $ (1.13 ) $ (0.49 ) $ (0.44 ) Shares used to compute basic and diluted net loss per share 20,894,353 23,592,763 27,705,472 27,780,212 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

The Company and Basis of Pres_2

The Company and Basis of Presentation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 218,735	$ 149,390
Cash and cash equivalents	$ 74,562	$ 60,813	$ 85,367	$ 62,562
Number of operating segments | segment	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018
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 Accoun_5

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, 2018	Dec. 31, 2017
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)	21,362,309	3,125,809
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)	12,517,328	17,331
Series X Convertible Preferred stock
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)	4,452,310	0
Common stock options, RSUs and PRSUs 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)	4,392,671	3,099,173
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)	0	9,305

Short-Term Investments (Details

Short-Term Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,509
Unrealized Gains	0
Unrealized Losses	(8)
Fair Value	$ 14,501	$ 0
Maturity of available-for-sale securities (less than) (term)	1 year
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,509
Unrealized Gains	0
Unrealized Losses	(8)
Fair Value	$ 14,501

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	May 21, 2018USD ($)closing	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent forward purchase obligations	$ 4,300,000	$ 411,000
Change in fair value of contingent forward purchase obligation		$ 3,851,000	$ 0	$ 0
Registered direct offering
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Aggregate value of shares authorized to be sold	$ 120,000,000
Number of direct offering closings | closing	3

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	May 21, 2018	Dec. 31, 2017
Assets:
Short-term investments	$ 0		$ 14,501
Assets at fair value	74,077		74,657
Liabilities:
Contingent forward purchase obligations	411	$ 4,300
Total liabilities at fair value	411
LEVEL 1
Assets:
Assets at fair value	74,077		11,556
Liabilities:
Contingent forward purchase obligations	0
Total liabilities at fair value	0
LEVEL 2
Assets:
Assets at fair value	0		63,101
Liabilities:
Contingent forward purchase obligations	0
Total liabilities at fair value	0
LEVEL 3
Assets:
Assets at fair value	0		0
Liabilities:
Contingent forward purchase obligations	411
Total liabilities at fair value	411
Money market funds
Assets:
Assets	74,077		11,556
Money market funds | LEVEL 1
Assets:
Assets	74,077		11,556
Money market funds | LEVEL 2
Assets:
Assets	0		0
Money market funds | LEVEL 3
Assets:
Assets	$ 0		0
U.S. Treasury reverse repurchase agreements
Assets:
Assets			48,000
U.S. Treasury reverse repurchase agreements | LEVEL 1
Assets:
Assets			0
U.S. Treasury reverse repurchase agreements | LEVEL 2
Assets:
Assets			48,000
U.S. Treasury reverse repurchase agreements | LEVEL 3
Assets:
Assets			0
Corporate debt
Assets:
Short-term investments			15,101
Corporate debt | LEVEL 1
Assets:
Short-term investments			0
Corporate debt | LEVEL 2
Assets:
Short-term investments			15,101
Corporate debt | LEVEL 3
Assets:
Short-term investments			$ 0

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,255	$ 3,064
Less accumulated depreciation and amortization	(2,543)	(2,020)
Total	712	1,044
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,114	2,051
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	455	327
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	119	119
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Depreciation and amortization of property and equipment	$ 523	$ 667	$ 732

Debt - Additional Information (

Debt - Additional Information (Details) - USD ($)	Jul. 27, 2018	Oct. 03, 2016	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Shares of common stock issued upon exercise of warrant (in shares)		17,331
Warrants exercise price (in dollars per share)		$ 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
Prepayment fee percentage in year one		2.00%
Prepayment fee percentage in year two		1.00%
Stated interest rate	4.50%		6.25%
Term Loan | Loan Agreement | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.75%
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			$ 56,000	$ 78,000
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, 2018USD ($)
Year ended:
December 31, 2019	$ 1,667
December 31, 2020	4,000
December 31, 2021	4,000
December 31, 2022	333
Total future principal payments due under the Term A Loan	$ 10,000

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details)	May 23, 2018USD ($)$ / sharesshares	May 21, 2018USD ($)closingday$ / sharesshares	Oct. 13, 2016USD ($)$ / sharesshares	May 31, 2018$ / sharesshares	Oct. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2018USD ($)vote_per_share$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)shares	Oct. 03, 2016$ / shares
Class of Stock [Line Items]
Recognition of beneficial conversion feature | $	$ 10,300,000					$ 10,329,000	$ 0	$ 0
Share price allowing the reduction of the aggregate offering size (in dollars per share) | $ / shares		$ 6.81
Weighted average share price allowing reduction of aggregate offering size (in dollars per share) | $ / shares				$ 6.27
Share price (in dollars per share) | $ / shares						$ 6.27
Number of common shares reduced by each preferred share sold (in shares)		10
Exercise price of warrant (in dollars per share) | $ / shares									$ 11.54
Term of warrants following closing of first closing of the offering		120 days
Preferred stock, shares authorized (in shares)						10,000,000	10,000,000
Preferred stock, par value (in dollars per share) | $ / shares						$ 0.0001	$ 0.0001
Preferred stock outstanding (in shares)						0
Common stock, shares authorized (in shares)						200,000,000	200,000,000
Number of votes for each share held | vote_per_share						1
Dividends in arrears or default | $						$ 0
Issuance of stock | $						6,440,000	$ 20,771,000	$ 26,622,000
Registered direct offering
Class of Stock [Line Items]
Aggregate value of shares authorized to be sold | $		$ 120,000,000
Number of direct offering closings | closing		3
Issuance of stock | $						$ 45,458,000
Registered direct offering, first closing
Class of Stock [Line Items]
Shares sold (in shares)	6,185,987
Offering price (in dollars per share) | $ / shares	$ 4.70
Registered direct offering, third closing
Class of Stock [Line Items]
Aggregate value of shares authorized to be sold | $		$ 20,000,000
Option fee paid by investors relating to third closing | $	$ 500,000
Threshold trading days | day		5
Registered direct offering, second closing
Class of Stock [Line Items]
Aggregate value of shares authorized to be sold | $		$ 50,000,000
Offering price (in dollars per share) | $ / shares		$ 4.70
Minimum value of shares purchased in order to participate in second closing | $		$ 1,000,000
Percent of the price per share of the volume weighted average price of common stock for the five trading days following the Company's public release of data		75.00%
Threshold trading days | day		5
Registered direct offering, first closing and First Private Placement
Class of Stock [Line Items]
Net proceeds | $	49,500,000
Second Private Placement
Class of Stock [Line Items]
Shares sold (in shares)		2,500,000
Offering price (in dollars per share) | $ / shares		$ 0.125
Private Placement
Class of Stock [Line Items]
Shares sold (in shares)					3,360,000
Offering price (in dollars per share) | $ / shares					$ 6
Net proceeds | $					$ 18,900,000
Controlled equity sales agreement with Cantor Fitzgerald & Co
Class of Stock [Line Items]
Shares sold (in shares)						847,937	240,178
Net proceeds | $						$ 6,400,000	$ 1,800,000
Series X Convertible Preferred Stock
Class of Stock [Line Items]
Beneficial conversion feature fair value | $	$ 10,300,000
Common stock issued for each preferred stock (in shares)		10		10
Preferred stock, shares authorized (in shares)				5,000,000		5,000,000	0
Preferred stock, par value (in dollars per share) | $ / shares				$ 0.0001		$ 0.0001	$ 0.0001
Preferred stock issued (in shares)						445,231	0
Preferred stock outstanding (in shares)						445,231	0
Maximum ownership following conversion				9.99%
Series X Convertible Preferred Stock | Registered direct offering
Class of Stock [Line Items]
Issuance of stock (in shares)						445,231
Series X Convertible Preferred Stock | Registered direct offering, first closing
Class of Stock [Line Items]
Shares sold (in shares)	445,231
Offering price (in dollars per share) | $ / shares	$ 47
Common stock warrants | First Private Placement
Class of Stock [Line Items]
Shares sold (in shares)	12,499,997
Offering price (in dollars per share) | $ / shares	$ 0.125
Exercise price of warrant (in dollars per share) | $ / shares		$ 6.81
Term of warrant		5 years
Common stock warrants | Second Private Placement
Class of Stock [Line Items]
Term of warrant		5 years
Common Stock
Class of Stock [Line Items]
Issuance of stock (in shares)			2,752,637			847,937	3,600,178	2,752,637
Shares issued, price per share (in dollars per share) | $ / shares			$ 10.10
Issuance of stock | $			$ 26,600,000				$ 0	$ 1,000
Common Stock | Registered direct offering
Class of Stock [Line Items]
Issuance of stock (in shares)						6,185,987
Issuance of stock | $						$ 1,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Total (in shares)	22,738,424	4,503,686
Common stock warrants
Class of Stock [Line Items]
Total (in shares)	12,517,328	17,331
Series X Convertible Preferred Stock
Class of Stock [Line Items]
Total (in shares)	4,452,310	0
Stock options, RSUs and PRSUs issued and outstanding
Class of Stock [Line Items]
Total (in shares)	4,392,671	3,099,173
Authorized for future stock awards
Class of Stock [Line Items]
Total (in shares)	669,873	1,006,307
Awards available under the ESPP
Class of Stock [Line Items]
Total (in shares)	706,242	380,875

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,710,000	$ 5,714,000
Weighted average grant date fair values of stock options granted (USD per share)	$ 2.98
Grant date fair value of stock options, vested	$ 3,600,000
Unrecognized share-based compensation expense of unvested employee stock options	$ 5,400,000
Unvested stock options, unrecognized cost expected to be recognized (in years)	2 years 3 months 22 days
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)	158,066
Unvested stock options, unrecognized cost expected to be recognized (in years)	8 months 12 days
Unrecognized share-based compensation expense of unvested employee stock options	$ 800,000
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	$ 0	$ 21,000
Restricted Stock | Common stock subject to repurchase
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares	0
RSUs and PRSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 300,000
Unrecognized share-based compensation expense of unvested employee stock options	$ 1,000,000
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) - RSUs and PRSUs	12 Months Ended
	Dec. 31, 2018shares
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)	227,500
Granted (in shares)	55,000
Vested (in shares)	(2,500)
Canceled (in shares)	(20,000)
Outstanding, end of period (in shares)	260,000

Equity Incentive Plans - Summ_2

Equity Incentive Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Beginning balance (in shares)	3,099,173
Granted (in shares)	1,436,250
Exercised (in shares)	(89,031)
Canceled (in shares)	(313,721)
Ending balance (in shares)	4,132,671	3,099,173
Weighted Average Exercise Price
Beginning balance (USD per share)	$ 7.74
Granted (USD per share)	4.22
Exercised (USD per share)	2.29
Canceled (USD per share)	8.41
Ending balance (USD per share)	$ 6.58	$ 7.74
Stock Options, Additional Disclosures
Weighted average remaining contractual life, Outstanding	7 years 4 months 28 days	8 years 1 month 6 days
Total aggregate intrinsic value, Outstanding	$ 25	$ 2,264
Vested and expected to vest (in shares)	4,132,671
Weighted average exercise price of shares vested and expected to vest (USD per share)	$ 6.58
Weighted average remaining contractual life of shares vested and expected to vest (in years)	7 years 4 months 28 days
Total aggregate intrinsic value of shares vested and expected to vest	$ 25
Exercisable (in shares)	2,423,061
Weighted average exercise price of shares exercisable (USD per share)	$ 7.29
Weighted average remaining contractual life of shares exercisable (in years)	6 years 8 months 27 days
Total aggregate intrinsic value of shares exercisable	$ 25

Equity Incentive Plans - Summ_3

Equity Incentive Plans - Summary of Black-Scholes Option Pricing Model Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum (as a percentage)	2.14%	1.05%
Risk-free interest rate, maximum (as a percentage)	2.81%	1.77%
Expected dividend yield (as a percentage)	0.00%	0.00%
Expected volatility, minimum (as a percentage)	77.00%	79.00%
Expected volatility, maximum (as a percentage)	92.00%	102.00%
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)	2.55%	1.87%
Risk-free interest rate, maximum (as a percentage)	3.06%	2.23%
Expected volatility	83.00%
Expected dividend yield (as a percentage)	0.00%	0.00%
Expected volatility, minimum (as a percentage)		79.00%
Expected volatility, maximum (as a percentage)		86.00%
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 - Summ_4

Equity Incentive Plans - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,710	$ 5,714
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,676	2,428
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 3,034	$ 3,286

Equity Incentive Plans - Summ_5

Equity Incentive Plans - Summary of Warrant Activity (Details) - Warrant - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Warrants
Outstanding at end of period (in shares)	12,517,328
Issued (in shares)	12,499,997
Exercised (in shares)	0
Canceled (in shares)	0
Outstanding at beginning of period (in shares)	17,331
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 11.54
Issued (in dollars per share)	6.81
Exercised (in dollars per share)	0
Canceled (in dollars per share)	0
Outstanding at end of period (in dollars per share)	$ 6.82
Total Intrinsic Value	$ 0	$ 0

Significant Agreements and Co_2

Significant Agreements and Contracts (Details) - Subaward Agreement - USD ($) $ in Millions	Mar. 30, 2017	May 31, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Grant Receivable, Duration Of Award		5 years
Grants Receivable		$ 5.5
CD201 product candidate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [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
Agreement termination, written notice period	30 days

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal income taxes at 21%	$ (12,393)	$ (18,947)	$ (16,334)
State income tax, net of federal benefit	0	0	(1)
Tax effect on nondeductible expenses	(278)	3,389	1,650
Research credits	(4,737)	(8,125)	(3,538)
Rate change	0	0	267
Change in valuation allowance	16,421	5,133	14,996
Reserve for uncertain tax positions	1,184	1,451	2,883
Tax Cuts and Jobs Act	0	17,334	0
Other	(197)	(235)	77
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating losses	$ 38,268	$ 26,364
Research credits	14,007	10,232
Intangibles	241	265
Other	2,488	1,722
Total deferred tax assets	55,004	38,583
Less valuation allowance	(55,004)	(38,583)
Income tax expense	$ 0	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Deferred tax assets, valuation allowance	$ 55,004	$ 38,583
Provisional income tax expense due to The Tax Cuts and Jobs Act	17,300
Unrecognized tax benefits	16,524	$ 10,756	$ 4,642	$ 356
Unrecognized tax benefits that would impact on effective tax rate	13,400
Federal
Income Tax Contingency [Line Items]
Net operating loss carryforwards	179,100
Tax credit carryforwards, research and development	17,000
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards	132,000
Tax credit carryforwards, research and development	$ 2,400

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecognized tax benefits
Balance as of the beginning of the year	$ 10,756	$ 4,642	$ 356
Increases related to current year tax positions	1,224	2,149	921
Increases related to prior year tax positions	4,544	3,965	3,365
Balance as of the end of the year	$ 16,524	$ 10,756	$ 4,642

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)optionclaim1	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
Number of claims and actions pending | claim1		0
Operating leases renewal term (in years)		2 years
Number of operating lease options for extension | option		2
Annual increase in base rent (as a percent)		3.00%
Lease rent expense		$ 776,000	$ 704,000
Contractual obligation, contract termination notice period		30 days
Scenario, Forecast
Loss Contingencies [Line Items]
Operating leases renewal term (in years)	36 months
Base Rent, Monthly Rate	$ 70,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payment (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,019	$ 836
2,020	861
2,021	887
Total minimum lease payments	$ 2,584

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Operating expenses	$ 16,598	$ 14,725	$ 15,152	$ 16,810	$ 13,459	$ 12,249	$ 16,615	$ 13,398	$ 63,285	$ 55,721	$ 48,436
Other income (expense)	4,256	1,106	(1,154)	61	31	(8)	(30)	0
Net loss	$ (12,342)	$ (13,619)	$ (16,306)	$ (16,749)	$ (13,428)	$ (12,257)	$ (16,645)	$ (13,398)	$ (59,016)	$ (55,728)	$ (48,165)
Basic and diluted net loss per common share (USD per share)	$ (0.44)	$ (0.49)	$ (1.13)	$ (0.80)	$ (0.69)	$ (0.73)	$ (0.99)	$ (0.80)	$ (2.76)	$ (3.18)	$ (3.32)
Shares used to compute basic and diluted net loss per common share (in shares)	27,780,212	27,705,472	23,592,763	20,894,353	19,489,375	16,864,211	16,831,960	16,795,366	25,142,976	17,500,853	14,488,987