Cidara Therapeutics (CDTX) 10-K 15 Mar 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Feb. 28, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	CDTX
Entity Registrant Name	Cidara Therapeutics, Inc.
Entity Central Index Key	1,610,618
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		16,801,184
Entity Public Float			$ 118.6

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 85,367	$ 62,562
Short-term investments	19,252	44,952
Prepaid expenses and other current assets	779	704
Total current assets	105,398	108,218
Property and equipment, net	1,374	1,684
Other assets	190	72
Total assets	106,962	109,974
Current liabilities:
Accounts payable	2,909	3,095
Accrued liabilities	3,338	1,415
Accrued compensation and benefits	2,662	1,464
Total current liabilities	8,909	5,974
Term loan, less debt issuance costs	9,794	0
Other long-term liabilities	80	88
Total liabilities	18,783	6,062
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized and no shares issued or outstanding at December 31, 2016 and 2015, respectively	0	0
Common stock, $0.0001 par value; 200,000,000 shares authorized at December 31, 2016 and 2015; 16,837,126 and 16,773,232 shares issued and outstanding, respectively, at December 31, 2016; 13,942,520 and 13,786,285 shares issued and outstanding, respectively, at December 31, 2015	2	1
Additional paid-in capital	181,840	149,416
Accumulated other comprehensive loss	(1)	(8)
Accumulated deficit	(93,662)	(45,497)
Total stockholders' equity	88,179	103,912
Total liabilities and stockholders' equity	$ 106,962	$ 109,974

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	16,837,126	13,942,520
Common stock, shares outstanding (in shares)	16,771,314	13,786,285

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development	$ 35,699	$ 23,475	$ 6,710
Cost of in-process research and development acquired	0	0	1,607
General and administrative	12,737	8,838	3,306
Total operating expenses	48,436	32,313	11,623
Loss from operations	(48,436)	(32,313)	(11,623)
Other income (expense):
Interest income (expense), net	271	120	(88)
Change in fair value of convertible notes payable	0	0	(183)
Total other income (expense)	271	120	(271)
Net loss	(48,165)	(32,193)	(11,894)
Other comprehensive income (loss):
Unrealized gain (loss) on short-term investments	7	(8)	0
Comprehensive loss	$ (48,158)	$ (32,201)	$ (11,894)
Basic and diluted net loss per share (USD per share)	$ (3.32)	$ (3.25)	$ (14.51)
Shares used to compute basic and diluted net loss per share (in shares)	14,488,987	9,920,382	819,868

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	IPO	IPOSeries A Convertible Preferred Stock	IPOSeries B Convertible Preferred Stock	Common Stock	Common StockIPO	Additional Paid-In Capital	Additional Paid-In CapitalIPO	Accumulated Deficit	Other Comprehensive Income (Loss)
Balance, beginning (in shares) at Dec. 31, 2013		0					366,552
Balance, beginning at Dec. 31, 2013	$ (1,398)	$ 0					$ 0		$ 12		$ (1,410)	$ 0
Issuance of stock (in shares)		89,360,118
Issuance of stock	0	$ 29,866							0
Conversion of Series A and Series B convertible preferred upon initial public offering (in shares)		8,165,963
Conversion of Series A and Series B convertible preferred upon initial public offering	0	$ 2,682							0
Issuance of common stock for in-process research and development (in shares)							703,092
Issuance of common stock for in-process research and development	1,607								1,607
Stock-based compensation	232								232
Vesting of restricted shares (in shares)							61,913
Vesting of restricted shares	5								5
Issuance of common stock for exercise of stock options (in shares)							1,181
Issuance of common stock for exercise of stock options	3								3
Issuance of warrants in connection with term loan	0
Unrealized gain (loss) on short-term investments	0
Net loss	(11,894)										(11,894)
Balance, ending (in shares) at Dec. 31, 2014		97,526,081	0				1,132,738
Balance, ending at Dec. 31, 2014	(11,445)	$ 32,548	$ 0				$ 0		1,859		(13,304)	0
Issuance of stock (in shares)			94,533,183				4,800,000
Issuance of stock	69,271		$ 41,921						69,271
Conversion of Series A and Series B convertible preferred upon initial public offering (in shares)					(97,526,081)	(94,533,183)		7,561,380
Conversion of Series A and Series B convertible preferred upon initial public offering				$ 74,469	$ (32,548)	$ (41,921)		$ 1		$ 74,468
Stock-based compensation	3,033								3,033
Vesting of restricted shares (in shares)							249,465
Vesting of restricted shares	499								499
Issuance of common stock for exercise of stock options (in shares)							23,538
Issuance of common stock for exercise of stock options	61								61
Issuance of common stock under Employee Stock Purchase Plan (in shares)							19,164
Issuance of common stock under Employee Stock Purchase Plan	225								225
Issuance of warrants in connection with term loan	0
Unrealized gain (loss) on short-term investments	(8)											(8)
Net loss	(32,193)										(32,193)
Balance, ending (in shares) at Dec. 31, 2015		0	0				13,786,285
Balance, ending at Dec. 31, 2015	103,912	$ 0	$ 0				$ 1		149,416		(45,497)	(8)
Issuance of stock (in shares)							2,752,637
Issuance of stock	26,622						$ 1		26,621
Stock-based compensation	4,344								4,344
Vesting of restricted shares (in shares)							90,423
Vesting of restricted shares	$ 197								197
Issuance of common stock for exercise of stock options (in shares)	83,353						83,353
Issuance of common stock for exercise of stock options	$ 525								525
Issuance of common stock under Employee Stock Purchase Plan (in shares)							58,616
Issuance of common stock under Employee Stock Purchase Plan	562								562
Issuance of warrants in connection with term loan	175								175
Unrealized gain (loss) on short-term investments	7											7
Net loss	(48,165)										(48,165)
Balance, ending (in shares) at Dec. 31, 2016							16,771,314
Balance, ending at Dec. 31, 2016	$ 88,179						$ 2		$ 181,840		$ (93,662)	$ (1)

Consolidated Statements of Con6

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Issuance costs	$ 0	$ 0	$ 233
Series A Convertible Preferred Stock
Issuance costs			$ 159
Series B Convertible Preferred Stock
Issuance costs		$ 99

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net loss	$ (48,165)	$ (32,193)	$ (11,894)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	732	461	179
Stock-based compensation	4,344	3,033	232
Non-cash interest expense	17	0	66
Amortization of discount or premium on short-term investments	(176)	(42)	0
Change in fair value of convertible notes payable	0	0	183
Amortization of debt issue costs	5	22	23
Deferred rent	(8)	54	34
Purchase of in-process research and development	0	0	1,607
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(76)	(487)	(204)
Accounts payable and accrued liabilities	1,913	2,143	1,746
Accrued compensation	1,760	1,050	414
Other assets	(117)	0	(96)
Net cash used in operating activities	(39,771)	(25,959)	(7,710)
Investing activities:
Purchases of short-term investments	(69,617)	(54,918)	0
Maturities of short-term investments	95,500	10,000	0
Purchases of property and equipment	(401)	(1,170)	(991)
Net cash provided by (used in) investing activities	25,482	(46,088)	(991)
Financing activities:
Proceeds form issuance of common stock, net of offering costs	26,622	69,505	0
Proceeds from issuance of Term Loan, net of offering costs	9,947	0	0
Proceeds from issuance of convertible notes payable, net of offering costs	0	0	930
Proceeds from exercise of stock options	525	387	749
Deferred initial public offering costs	0	0	(233)
Net cash provided by financing activities	37,094	111,813	31,312
Net increase in cash and cash equivalents	22,805	39,766	22,611
Cash and cash equivalents at beginning of year	62,562	22,796	185
Cash and cash equivalents at end of year	85,367	62,562	22,796
Non-cash investing activity:
Property and equipment acquired but not yet paid	21	113	51
Non-cash financing activities:
Deferred initial public offering costs	0	234	146
Conversion of convertible notes payable and accrued interest to Series A convertible preferred shares	0	0	2,682
Issuance of warrants to purchase common stock upon execution of term loan	175	0	0
Vesting of early exercised stock options	197	499	0
Purchase of shares pursuant to Employee Stock Purchase Plan	562	0	0
Series A Convertible Preferred Stock
Financing activities:
Proceeds from issuance of convertible preferred stock	0	0	29,866
Deferred initial public offering costs			(159)
Non-cash financing activities:
Conversion of convertible preferred stock to common upon initial public offering	0	32,548	0
Series B Convertible Preferred Stock
Financing activities:
Proceeds from issuance of convertible preferred stock	0	41,921	0
Deferred initial public offering costs		(99)
Non-cash financing activities:
Conversion of convertible preferred stock to common upon initial public offering	$ 0	$ 41,921	$ 0

The Company and Basis of Presen

The Company and Basis of Presentation	12 Months Ended
	Dec. 31, 2016
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 initial product portfolio is comprised of proprietary product candidates for the treatment of serious fungal and bacterial infections. In March 2016, the Company formed a wholly-owned subsidiary, Cidara Therapeutics UK Limited, in England for the purpose of developing its product candidates in Europe. Basis of Presentation The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The Company has experienced net losses and negative cash flows from operating activities since its inception. At December 31, 2016 , the Company had an accumulated deficit of $93.7 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. The Company plans to continue to fund its losses from operations and capital funding needs through debt and equity financing, through government funding or through collaborations or partnerships with other entities. Debt or equity financing or collaborations and partnerships with other entities may not be available on a timely basis on terms acceptable to the Company, or at all. If the Company is not able to secure adequate additional funding, the Company may be forced to d elay, reduce or eliminate its research and development programs or future commercialization efforts, or to make reductions in spending, extend payment terms with suppliers, liquidate or grant rights to assets where possible, or suspend or curtail planned programs. 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 subsidiary. All significant intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates —The preparation of financial statements in conformity with U.S. generally accepted accounting principles, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The Company evaluates its estimates and assumptions on an ongoing basis. The most significant estimates in the Company’s consolidated financial statements relate to estimating the fair value of the Company’s common shares used to account for share-based compensation and certain accruals, including those related to preclinical and clinical activities. Although the estimates are based on the Company’s knowledge of current events, comparable companies, and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. Segment Information —Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Cash and Cash Equivalents —The Company considers all short-term investments purchased with a maturity of three months or less when acquired to be cash equivalents. Investments Available-for-Sale — Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive income (loss). The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. The amortization of premiums and accretion of discounts is included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. Securities with maturity dates of 12 months or less from the date of purchase are classified as short-term investments and securities with maturity dates of more than 12 months are classified as long-term investments. Property and Equipment — We carry our 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 and 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. Research and Development Costs —Research and development expenses consist of wages, benefits and stock-based compensation charges for research and development employees, scientific consultant fees, facilities and overhead expenses, laboratory supplies, manufacturing expenses, and preclinical and clinical trial costs. The Company accrues 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 marketable securities. Comprehensive gains (losses) have been reflected in the 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, restricted stock grants, and employee stock purchase plan rights by estimating the fair value on the date of grant using the Black-Scholes option pricing model. For awards subject to time-based vesting conditions, stock-based compensation expense is recognized ratably over the requisite service period of the awards. The Company accounts for stock options granted to non-employees using the fair value approach. These option grants are subject to periodic revaluation over their vesting terms. Net Loss Per Share —Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of convertible preferred stock, convertible notes payable, unvested restricted common stock subject to repurchase, and options outstanding under the Company’s stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in common stock equivalent shares): December 31, 2016 2015 Common stock options issued and outstanding 2,295,393 1,437,583 Common stock warrants 17,331 — Common stock subject to repurchase 63,894 156,235 Total 2,376,618 1,593,818 Fair Value of Financial Instruments — The Company follows authoritative guidance with respect to fair value reporting issued by the FASB for financial assets and liabilities, which defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The Company’s financial instruments consist of cash and cash equivalents, marketable securities, prepaid expenses, accounts payable, accrued liabilities and long-term debt. Fair value estimates of these instruments are made at a specific point in time based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, prepaid expenses, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. The fair value of short-term investments is based upon market prices quoted on the last day of the fiscal period or other observable market inputs. The Company believes that the fair value of long-term debt approximates its carrying value. Recently Issued Accounting Standards — During 2014, the FASB issued Accounting Standards Update (“ASU”) 2014-15, “ Presentation of Financial Statements—Going Concern, ” which requires management to assess an entity’s ability to continue as a going concern and to provide related footnote disclosure in certain circumstances. The update is effective for annual reporting periods ending after December 15, 2016 and interim periods thereafter. The Company adopted ASU 2014-15 in the fourth quarter of 2016. The adoption of this guidance did not have a material impact on the Company's consolidated financial statements. During 2015, the FASB issued ASU 2015-03, " Interest - Imputation of Interest: Simplifying the Presentation of Debt Issuance Costs ," which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The updated guidance is effective or interim and annual periods beginning after December 15, 2015. The Company adopted ASU 2015-03 in 2016. The adoption of this guidance did not have a material impact on the Company's consolidated financial statements. During 2015, the FASB issued 2015-17, " Income Taxes: Balance Sheet Classification of Deferred Assets ," which requires reporting entities to classify deferred income taxes as non-current on the consolidated balance sheets and simplifies the presentation of deferred income taxes. The updated guidance is effective for annual reporting periods beginning after December 15, 2016, and early adoption is permitted. The Company early adopted ASU 2015-17 in the fourth quarter of 2016. the adoption of this guidance did not have a material impact on the Company's consolidated financial statements. During 2016, the FASB issued ASU 2016-09, " Compensation – Stock Compensation: Improvements to Employee Share-Based Payment Accounting ,” which simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The updated guidance is effective for interim and annual periods beginning after December 15, 2016, and early adoption is permitted. The Company early adopted ASU 2016-09 in the fourth quarter of 2016. The adoption of this guidance did not have a material impact on the Company's consolidated financial statements. During 2014, the FASB issued ASU 2014-09, "Revenue from Contracts with Customers," which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2015-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Although the Company does not have any revenue contracts, in the event the Company signs a collaboration or other revenue generating contract during 2017 we would anticipate early adopting this standard using the full retrospective method of adoption so that, in the event we enter into any revenue contracts, the contracts will be accounted for under the new guidance from inception of the contract. During 2016, the FASB issued ASU 2016-01, “ Recognition and Measurement of Financial Assets and Financial Liabilities ,” which eliminates the requirement for public companies to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet. The standard also requires public entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes. Furthermore, the standard requires presentation of assets and liabilities by measurement category and form of financial asset on the balance sheet or accompanying notes to the financial statements. The updated guidance is effective for interim and annual periods beginning after December 15, 2017, and early adoption is permitted. The Company is currently assessing the impact that this standard will have on its consolidated financial statements. During 2016, the FASB issued ASU 2016-02, “ 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 is currently assessing the impact that this standard will have on its consolidated financial statements. During 2016, the FASB issued ASU 2016-15, " Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments, " which addresses the presentation and classification of certain cash receipts and payments in the statement of cash flows. The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2017, and early adoption is permitted. The adoption of this guidance is not expected to have a material impact on the Company's consolidated financial statements.

Short-Term Investments

Short-Term Investments	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Short-Term Investments	SHORT-TERM INVESTMENTS The following table summarizes the available-for-sale securities held at December 31, 2016 and 2015 (in thousands): As of December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Commercial paper $ 19,253 $ 1 $ (2 ) $ 19,252 Total $ 19,253 $ 1 $ (2 ) $ 19,252 As of December 31, 2015 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Certificates of deposit $ 20,000 $ — $ — $ 20,000 Commercial paper 24,960 — (8 ) 24,952 Total $ 44,960 $ — $ (8 ) $ 44,952 All available-for-sale securities held at December 31, 2016 and 2015 mature in less than one year. Unrealized gains and losses on available-for-sale securities are included as a component of other comprehensive loss. The securities in unrealized loss positions have not been in a continuous unrealized loss position for 12 months or longer. The Company does not intend to sell the investments and it is not more likely than not that the Company will be required to sell the investments before recovery of their amortized cost bases which may be at maturity. The Company reviews its investments to identify and evaluate investments that have an indication of possible other-than-temporary impairment. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition and near-term prospects of the investee, and the Company’s intent and ability to hold the investment for a period of time sufficient to allow for any anticipated recovery in market value.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
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 that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-tier fair value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions, which reflect those that a market participant would use. At December 31, 2016 and 2015, the Company held commercial paper, which is valued using observable market inputs including reported trades, broker/dealer quotes, bids and/or offers, and securities of money market funds, which invested in short-term U.S. Treasury securities, the prices of which were available from quoted prices in active markets. At December 31, 2015, the Company held certificates of deposit, which are valued at cost. 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, 2016 Assets: Cash equivalents and money market funds $ 84,830 $ 84,830 $ — $ — Commercial paper 19,252 — 19,252 — Total assets at fair value $ 104,082 $ 84,830 $ 19,252 $ — December 31, 2015 Assets: Cash equivalents and money market funds $ 12,353 $ 12,353 $ — $ — Certificates of deposit included in cash and cash equivalents 50,000 — 50,000 — Certificates of deposit included in short-term investments 20,000 — 20,000 — Commercial paper 24,952 — 24,952 — Total assets at fair value $ 107,305 $ 12,353 $ 94,952 $ —

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Property and Equipment	PROPERTY AND EQUIPMENT Property and equipment consisted of the following (in thousands): December 31, 2016 2015 Laboratory equipment $ 1,771 $ 1,438 Leasehold improvements 425 425 Computer hardware and software 295 242 Office equipment 111 111 Furniture and fixtures 142 105 2,744 2,321 Less accumulated depreciation and amortization (1,370 ) (637 ) Total $ 1,374 $ 1,684 Depreciation and amortization of property and equipment of $732,000 and $461,000 were recorded for the years ended December 31, 2016 and 2015 , respectively.

Debt

Debt	12 Months Ended
	Dec. 31, 2016
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, including the Company’s achievement of specified milestones in the Loan Agreement (the “Milestones”), the Company may, at its sole discretion through April 3, 2018 , borrow from the Lender up to an additional $10.0 million (the "Term B Loan", and together with Term A Loan, the "Term Loans"). The Loan Agreement also includes an operating covenant which requires the Company to achieve the Milestones on or before March 31, 2018 . The milestone event for the Term B Loan is the achievement of positive data from a Phase 2 clinical trial of CD101 Topical or CD101 IV. The Company’s obligations under the Loan Agreement are secured by a first priority security interest in substantially all of the Company’s current and future assets, other than its intellectual property, which is subject to a double negative pledge. The Term Loans mature on October 3, 2020 (the "Maturity Date"). Payments under the Term Loans will be interest-only through April 2, 2018 , which will be extended by six months if the Term B milestone event is achieved. The interest-only period will be followed by 30 equal monthly payments of principal and interest; provided that there will be 24 equal monthly payments if the Term B milestone amount is achieved. The Term Loans will bear interest at a variable annual rate equal to the greater of (i) 4.5% or (ii) the Lender’s prime interest rate plus 1.0% . At December 31, 2016, the Term Loans bear interest at 4.75% . The Company may prepay the borrowed amounts, provided that the Company will be obligated to pay a prepayment fee equal to (i) 2.0% of the applicable principal amount of the Term Loan if the prepayment occurs before the first anniversary of the applicable funding date, and (ii) 1.0% of the applicable principal amount of the Term Loan if the prepayment occurs after the first anniversary of the funding date of such Term Loan but on or prior to the second anniversary of the funding date of such Term Loan. Pursuant to the Loan Agreement, on October 3, 2016, the Company issued to the Lender a warrant to purchase an aggregate of up to 17,331 shares of the Company’s common stock at an exercise price of $11.54 per share. If the Company borrows additional amounts under the Loan Agreement, it will, in connection with any such borrowing, issue the Lender an additional warrant to purchase that number of shares of the Company’s common stock as is equal to 2.0% of the additional principal amount borrowed divided by the exercise price. The exercise price shall be equal to the 30 -day average closing price of the Company’s common stock, calculated as of the date immediately prior to the date of such additional borrowing. The warrants are immediately exercisable and will expire ten years from the date of the grant. While any amounts are outstanding under the Loan Agreement, the Company is subject to a number of affirmative and restrictive covenants, including covenants regarding dispositions of property, business combinations or acquisitions, incurring additional indebtedness and transactions with affiliates, among other customary covenants. The Company is also restricted from paying dividends or making other distributions or payments on its capital stock, subject to limited exceptions. Upon the occurrence of certain events, including but not limited to the Company’s failure to satisfy its payment obligations under the Loan Agreement, the breach of certain of its other covenants under the Loan Agreement, including the receipt of positive Phase 2 clinical data from either the CD101 topical or CD101 IV programs by March 31, 2018 , or the occurrence of a material adverse change, the collateral agent will have the right, among other remedies, to declare all principal and interest and other amounts due to the Lender under the Loan Agreement immediately due and payable. As of December 31, 2016 , future principal payments due under the Term A Loan are as follows (in thousands): Year ended: December 31, 2017 $ — December 31, 2018 2,667 December 31, 2019 4,000 December 31, 2020 3,333 Total future principal payments due under the Term A Loan $ 10,000 The fair value of the warrants to purchase common stock issued in connection with Term Loan A was estimated on the date of issuance using the Black-Scholes valuation model and recorded to additional paid-in capital. The fair value of the warrants on the date of issuance as well as the debt issue costs incurred in connection with the entry into the Loan Agreement are presented as a direct deduction from the carrying amount of the term loan on the consolidated balance sheet and will be amortized utilizing the effective interest method over the term of the loan. Amortization of the fair value of the warrants and debt issue costs was $ 17,000 and $ 5,000 , respectively, and each was recognized as a component of interest expense for the year ended December 31, 2016.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Stockholders' Equity	STOCKHOLDERS’ EQUITY Preferred Stock — Under the amended and restated certificate of incorporation, the Company’s board of directors has the authority, without further action by the stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each such series, to fix the rights, preferences and privileges of the shares of each wholly unissued series and any qualifications, limitations or restrictions thereon and to increase or decrease the number of shares of any such series, but not below the number of shares of such series then outstanding. The Company had 10,000,000 shares of preferred stock authorized and no shares of preferred stock issued or outstanding at December 31, 2016 . Common Stock —The Company had 200,000,000 shares of common stock authorized as of December 31, 2016 . 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. Common Stock Reserved for Future Issuance Common stock reserved for future issuance is as follows (in common stock equivalent shares): Years ended December 31, 2016 2015 Common stock warrants 17,331 — Stock options issued and outstanding 2,295,393 1,437,583 Authorized for future stock awards under the Company's option plans 1,404,933 1,788,396 Awards available under the ESPP 306,813 226,004 Total 4,024,470 3,451,983

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2016
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, restricted stock units, 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 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"). In addition, 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, or (ii) 490,336 shares. 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 under the ESPP are limited to 15% of the employee’s eligible compensation. During the year ended December 31, 2016 , 58,616 shares were issued pursuant to the ESPP. Restricted Stock The Company permits early exercise of certain stock options. Any unvested shares are restricted and subject to repurchase by the Company until the conditions for vesting are met. At December 31, 2016 and 2015 , the liabilities for the cash received from the early exercise of stock options were $144,000 and $341,000 , respectively, and were classified in accrued liabilities on the balance sheet. The Company reduces the liability as the underlying shares vest in accordance with the vesting terms outlined in the stock option agreements which, generally, is 4 years . At December 31, 2016 , 63,894 unvested shares were subject to repurchase by the Company. Stock Options The following table summarizes stock option activity during the year ended December 31, 2016 : Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Life in Years Total Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2015 1,437,583 $ 6.19 8.94 $ 15,774 Options granted 947,025 10.16 Options exercised (83,353 ) 6.30 Options canceled (5,862 ) 5.97 Outstanding at December 31, 2016 2,295,393 $ 7.82 8.20 $ 6,774 Vested and expected to vest at December 31, 2016 2,295,393 $ 7.82 8.20 $ 6,774 Exercisable at December 31, 2016 878,658 $ 7.05 8.15 $ 3,444 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, 2016 2015 2015 EIP Risk-free interest rate 1.14% - 2.09% 1.53% - 1.91% Expected dividend yield 0% 0% Expected volatility 80% - 82% 78% - 80% Expected term (years) 5.50 - 6.08 5.00 - 6.08 2015 ESPP Risk-free interest rate 0.48% - 1.08% 0.35% - 0.94% Expected dividend yield 0% 0% Expected volatility 80% - 107% 65% - 101% Expected term (years) 0.50 - 2.00 0.50 - 2.00 Stock-based compensation expense recognized for stock options and the ESPP has been reported in the statements of operations and comprehensive loss as follows (in thousands): Years ended December 31, 2016 2015 Research and development $ 2,005 $ 1,586 General and administrative 2,339 1,447 Total $ 4,344 $ 3,033 The weighted-average grant date fair value of stock options granted to employees during the year ended December 31, 2016 was $6.99 per share. The total grant date fair value of stock options that vested during the year ended December 31, 2016 was $3.6 million . As of December 31, 2016 , total unrecognized share-based compensation expense related to unvested employee stock options of the Company was approximately $7.8 million . This unrecognized compensation cost is expected to be recognized over a weighted-average period of approximately 2.14 years. As of December 31, 2016 , total unrecognized compensation expense related to the Company’s ESPP was approximately $0.6 million . This unrecognized compensation cost is expected to be recognized over approximately 1.9 years.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The Company accounts for income taxes under ASC 740. Deferred income tax assets and liabilities are determined based upon differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The following table provides a reconciliation between income taxes computed at the federal statutory rate of 34% and the provision for income taxes (in thousands): Years Ended December 31, 2016 2015 2014 Federal income taxes at 34% $ (16,334 ) $ (10,946 ) $ (4,044 ) State income tax, net of federal benefit (1 ) (1,821 ) (672 ) Tax effect on nondeductible expenses 1,650 341 132 Research credits (3,538 ) (676 ) (265 ) Rate change 267 — — Change in valuation allowance 14,996 13,084 4,849 Reserve for uncertain tax positions 2,883 — — Other 77 18 — Income tax expense $ — $ — $ — Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2016 2015 Deferred tax assets: Net operating losses $ 27,309 $ 15,646 Research credits 3,646 987 Intangibles 466 590 Other 2,030 1,231 Total deferred tax assets 33,451 18,454 Less valuation allowance (33,451 ) (18,454 ) Income tax expense $ — $ — At December 31, 2016 , the Company had federal and state net operating loss carryforwards of approximately $79.5 million and $39.1 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 $4.3 million and state research and development credit carryforwards totaling $0.9 million . The federal research and development credit and orphan drug credit carryforwards begin to expire in 2033, unless previously utilized. The state research and development credit carryforwards begin to expire in 2018. Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use the existing deferred tax assets. Based on the weight of all evidence, including a history of operating losses, management has determined that it is more likely than not that the net deferred tax assets will not be realized. A valuation allowance of $33.5 million and $18.5 million as of December 31, 2016 and 2015 , 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 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, 2016 and 2015 , the unrecognized tax benefits recorded were approximately $4.6 million and $0.4 million , respectively. Approximately $3.2 million of the unrecognized tax benefits would reduce our 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 2016, 2015 and 2014 is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Balance as of the beginning of the year $ 356 $ 108 $ 6 Increases related to current year tax positions 921 248 102 Increases related to prior year tax positions 3,365 — — Balance as of the end of the year $ 4,642 $ 356 $ 108 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, 2016
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, 2016 which will have, individually or in the aggregate, a material adverse effect on its business, liquidity, financial position, or results of operations. Litigation, however, is subject to inherent uncertainties, and an adverse result in such matters may arise from time to time that may harm the Company’s business. Lease Obligations —In June 2014, the Company entered into an operating lease agreement for laboratory and office space in San Diego, California. Amendments for additional space were entered into in February 2015, March 2015 and August 2015. The lease expires in December 2018 with options for two individual two -year extensions. The lease is subject to charges for common area maintenance and other costs, and base rent is subject to 3% annual increases every July. Rent expense is being recorded on a straight-line basis over the life of the lease. Future minimum payments required under the lease as of December 31, 2016 are summarized as follows (in thousands): 2017 $ 724 2018 746 Total minimum lease payments $ 1,470 Rent expense was $733,000 and $581,000 for the years ended December 31, 2016 and 2015 , 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, 2016
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter 2016 Operating expenses $ 9,885 $ 11,862 $ 12,336 $ 14,353 Other income (expense) 96 107 109 (41 ) Net loss (9,789 ) (11,755 ) (12,227 ) (14,394 ) Basic and diluted net loss per share $ (0.71 ) $ (0.85 ) $ (0.88 ) $ (0.88 ) Shares used to compute basic and diluted net loss per share 13,807,825 13,871,938 13,910,145 16,352,046 2015 Operating expenses $ 6,732 $ 6,446 $ 9,207 $ 9,928 Other income (expense) (5 ) 32 33 60 Net loss (6,737 ) (6,414 ) (9,174 ) (9,868 ) Basic and diluted net loss per share $ (5.92 ) $ (0.59 ) $ (0.67 ) $ (0.72 ) Shares used to compute basic and diluted net loss per share 1,138,911 10,957,150 13,674,568 13,731,519

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The Company has experienced net losses and negative cash flows from operating activities since its inception. At December 31, 2016 , the Company had an accumulated deficit of $93.7 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. The Company plans to continue to fund its losses from operations and capital funding needs through debt and equity financing, through government funding or through collaborations or partnerships with other entities. Debt or equity financing or collaborations and partnerships with other entities may not be available on a timely basis on terms acceptable to the Company, or at all. If the Company is not able to secure adequate additional funding, the Company may be forced to d elay, reduce or eliminate its research and development programs or future commercialization efforts, or to make reductions in spending, extend payment terms with suppliers, liquidate or grant rights to assets where possible, or suspend or curtail planned programs. Any of these actions could materially harm the Company’s business, results of operations and future prospects.
Basis of Consolidation	Basis of Consolidation — The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All significant intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates —The preparation of financial statements in conformity with U.S. generally accepted accounting principles, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The Company evaluates its estimates and assumptions on an ongoing basis. The most significant estimates in the Company’s consolidated financial statements relate to estimating the fair value of the Company’s common shares used to account for share-based compensation and certain accruals, including those related to preclinical and clinical activities. Although the estimates are based on the Company’s knowledge of current events, comparable companies, and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.
Segment Information	Segment Information —Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.
Cash and Cash Equivalents	Cash and Cash Equivalents —The Company considers all short-term investments purchased with a maturity of three months or less when acquired to be cash equivalents.
Investments Available-for-Sale	Investments Available-for-Sale — Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in accumulated other comprehensive income (loss). The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. The amortization of premiums and accretion of discounts is included in interest income. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income (expense). The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. Securities with maturity dates of 12 months or less from the date of purchase are classified as short-term investments and securities with maturity dates of more than 12 months are classified as long-term investments.
Property and Equipment	Property and Equipment — We carry our 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 and 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.
Research and Development Costs	Research and Development Costs —Research and development expenses consist of wages, benefits and stock-based compensation charges for research and development employees, scientific consultant fees, facilities and overhead expenses, laboratory supplies, manufacturing expenses, and preclinical and clinical trial costs. The Company accrues 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 marketable securities. Comprehensive gains (losses) have been reflected in the 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, restricted stock grants, and employee stock purchase plan rights by estimating the fair value on the date of grant using the Black-Scholes option pricing model. For awards subject to time-based vesting conditions, stock-based compensation expense is recognized ratably over the requisite service period of the awards. The Company accounts for stock options granted to non-employees using the fair value approach. These option grants are subject to periodic revaluation over their vesting terms.
Net Loss Per Share	Net Loss Per Share —Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of convertible preferred stock, convertible notes payable, unvested restricted common stock subject to repurchase, and options outstanding under the Company’s stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding.
Fair Value of Financial Instruments	Fair Value of Financial Instruments — The Company follows authoritative guidance with respect to fair value reporting issued by the FASB for financial assets and liabilities, which defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The Company’s financial instruments consist of cash and cash equivalents, marketable securities, prepaid expenses, accounts payable, accrued liabilities and long-term debt. Fair value estimates of these instruments are made at a specific point in time based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, prepaid expenses, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. The fair value of short-term investments is based upon market prices quoted on the last day of the fiscal period or other observable market inputs. The Company believes that the fair value of long-term debt approximates its carrying value.
Recently Issued Accounting Standards	Recently Issued Accounting Standards — During 2014, the FASB issued Accounting Standards Update (“ASU”) 2014-15, “ Presentation of Financial Statements—Going Concern, ” which requires management to assess an entity’s ability to continue as a going concern and to provide related footnote disclosure in certain circumstances. The update is effective for annual reporting periods ending after December 15, 2016 and interim periods thereafter. The Company adopted ASU 2014-15 in the fourth quarter of 2016. The adoption of this guidance did not have a material impact on the Company's consolidated financial statements. During 2015, the FASB issued ASU 2015-03, " Interest - Imputation of Interest: Simplifying the Presentation of Debt Issuance Costs ," which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The updated guidance is effective or interim and annual periods beginning after December 15, 2015. The Company adopted ASU 2015-03 in 2016. The adoption of this guidance did not have a material impact on the Company's consolidated financial statements. During 2015, the FASB issued 2015-17, " Income Taxes: Balance Sheet Classification of Deferred Assets ," which requires reporting entities to classify deferred income taxes as non-current on the consolidated balance sheets and simplifies the presentation of deferred income taxes. The updated guidance is effective for annual reporting periods beginning after December 15, 2016, and early adoption is permitted. The Company early adopted ASU 2015-17 in the fourth quarter of 2016. the adoption of this guidance did not have a material impact on the Company's consolidated financial statements. During 2016, the FASB issued ASU 2016-09, " Compensation – Stock Compensation: Improvements to Employee Share-Based Payment Accounting ,” which simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The updated guidance is effective for interim and annual periods beginning after December 15, 2016, and early adoption is permitted. The Company early adopted ASU 2016-09 in the fourth quarter of 2016. The adoption of this guidance did not have a material impact on the Company's consolidated financial statements. During 2014, the FASB issued ASU 2014-09, "Revenue from Contracts with Customers," which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. ASU 2015-09 outlines a five-step process for revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards, and also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Although the Company does not have any revenue contracts, in the event the Company signs a collaboration or other revenue generating contract during 2017 we would anticipate early adopting this standard using the full retrospective method of adoption so that, in the event we enter into any revenue contracts, the contracts will be accounted for under the new guidance from inception of the contract. During 2016, the FASB issued ASU 2016-01, “ Recognition and Measurement of Financial Assets and Financial Liabilities ,” which eliminates the requirement for public companies to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet. The standard also requires public entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes. Furthermore, the standard requires presentation of assets and liabilities by measurement category and form of financial asset on the balance sheet or accompanying notes to the financial statements. The updated guidance is effective for interim and annual periods beginning after December 15, 2017, and early adoption is permitted. The Company is currently assessing the impact that this standard will have on its consolidated financial statements. During 2016, the FASB issued ASU 2016-02, “ 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 is currently assessing the impact that this standard will have on its consolidated financial statements. During 2016, the FASB issued ASU 2016-15, " Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments, " which addresses the presentation and classification of certain cash receipts and payments in the statement of cash flows. The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2017, and early adoption is permitted. The adoption of this guidance is not expected to have a material impact on the Company's consolidated financial statements.

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2016 2015 Common stock options issued and outstanding 2,295,393 1,437,583 Common stock warrants 17,331 — Common stock subject to repurchase 63,894 156,235 Total 2,376,618 1,593,818

Short-Term Investments (Tables)

Short-Term Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Securities	The following table summarizes the available-for-sale securities held at December 31, 2016 and 2015 (in thousands): As of December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Commercial paper $ 19,253 $ 1 $ (2 ) $ 19,252 Total $ 19,253 $ 1 $ (2 ) $ 19,252 As of December 31, 2015 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Certificates of deposit $ 20,000 $ — $ — $ 20,000 Commercial paper 24,960 — (8 ) 24,952 Total $ 44,960 $ — $ (8 ) $ 44,952

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2016 Assets: Cash equivalents and money market funds $ 84,830 $ 84,830 $ — $ — Commercial paper 19,252 — 19,252 — Total assets at fair value $ 104,082 $ 84,830 $ 19,252 $ — December 31, 2015 Assets: Cash equivalents and money market funds $ 12,353 $ 12,353 $ — $ — Certificates of deposit included in cash and cash equivalents 50,000 — 50,000 — Certificates of deposit included in short-term investments 20,000 — 20,000 — Commercial paper 24,952 — 24,952 — Total assets at fair value $ 107,305 $ 12,353 $ 94,952 $ —

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following (in thousands): December 31, 2016 2015 Laboratory equipment $ 1,771 $ 1,438 Leasehold improvements 425 425 Computer hardware and software 295 242 Office equipment 111 111 Furniture and fixtures 142 105 2,744 2,321 Less accumulated depreciation and amortization (1,370 ) (637 ) Total $ 1,374 $ 1,684

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule of Future Principal Payments Due	As of December 31, 2016 , future principal payments due under the Term A Loan are as follows (in thousands): Year ended: December 31, 2017 $ — December 31, 2018 2,667 December 31, 2019 4,000 December 31, 2020 3,333 Total future principal payments due under the Term A Loan $ 10,000

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Common Stock Reserved for Future Issuance	Common stock reserved for future issuance is as follows (in common stock equivalent shares): Years ended December 31, 2016 2015 Common stock warrants 17,331 — Stock options issued and outstanding 2,295,393 1,437,583 Authorized for future stock awards under the Company's option plans 1,404,933 1,788,396 Awards available under the ESPP 306,813 226,004 Total 4,024,470 3,451,983

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Stock Option Activity	The following table summarizes stock option activity during the year ended December 31, 2016 : Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Life in Years Total Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2015 1,437,583 $ 6.19 8.94 $ 15,774 Options granted 947,025 10.16 Options exercised (83,353 ) 6.30 Options canceled (5,862 ) 5.97 Outstanding at December 31, 2016 2,295,393 $ 7.82 8.20 $ 6,774 Vested and expected to vest at December 31, 2016 2,295,393 $ 7.82 8.20 $ 6,774 Exercisable at December 31, 2016 878,658 $ 7.05 8.15 $ 3,444
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, 2016 2015 2015 EIP Risk-free interest rate 1.14% - 2.09% 1.53% - 1.91% Expected dividend yield 0% 0% Expected volatility 80% - 82% 78% - 80% Expected term (years) 5.50 - 6.08 5.00 - 6.08 2015 ESPP Risk-free interest rate 0.48% - 1.08% 0.35% - 0.94% Expected dividend yield 0% 0% Expected volatility 80% - 107% 65% - 101% Expected term (years) 0.50 - 2.00 0.50 - 2.00
Summary of Stock-Based Compensation Expense	Stock-based compensation expense recognized for stock options and the ESPP has been reported in the statements of operations and comprehensive loss as follows (in thousands): Years ended December 31, 2016 2015 Research and development $ 2,005 $ 1,586 General and administrative 2,339 1,447 Total $ 4,344 $ 3,033

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Reconciliation Between Federal Statutory and Provision For Income Taxes	The following table provides a reconciliation between income taxes computed at the federal statutory rate of 34% and the provision for income taxes (in thousands): Years Ended December 31, 2016 2015 2014 Federal income taxes at 34% $ (16,334 ) $ (10,946 ) $ (4,044 ) State income tax, net of federal benefit (1 ) (1,821 ) (672 ) Tax effect on nondeductible expenses 1,650 341 132 Research credits (3,538 ) (676 ) (265 ) Rate change 267 — — Change in valuation allowance 14,996 13,084 4,849 Reserve for uncertain tax positions 2,883 — — Other 77 18 — Income tax expense $ — $ — $ —
Schedule of Components of Net Deferred Tax Assets	Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2016 2015 Deferred tax assets: Net operating losses $ 27,309 $ 15,646 Research credits 3,646 987 Intangibles 466 590 Other 2,030 1,231 Total deferred tax assets 33,451 18,454 Less valuation allowance (33,451 ) (18,454 ) 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 2016, 2015 and 2014 is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Balance as of the beginning of the year $ 356 $ 108 $ 6 Increases related to current year tax positions 921 248 102 Increases related to prior year tax positions 3,365 — — Balance as of the end of the year $ 4,642 $ 356 $ 108

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2016 are summarized as follows (in thousands): 2017 $ 724 2018 746 Total minimum lease payments $ 1,470

Selected Quarterly Financial 29

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Data (Unaudited)	First Quarter Second Quarter Third Quarter Fourth Quarter 2016 Operating expenses $ 9,885 $ 11,862 $ 12,336 $ 14,353 Other income (expense) 96 107 109 (41 ) Net loss (9,789 ) (11,755 ) (12,227 ) (14,394 ) Basic and diluted net loss per share $ (0.71 ) $ (0.85 ) $ (0.88 ) $ (0.88 ) Shares used to compute basic and diluted net loss per share 13,807,825 13,871,938 13,910,145 16,352,046 2015 Operating expenses $ 6,732 $ 6,446 $ 9,207 $ 9,928 Other income (expense) (5 ) 32 33 60 Net loss (6,737 ) (6,414 ) (9,174 ) (9,868 ) Basic and diluted net loss per share $ (5.92 ) $ (0.59 ) $ (0.67 ) $ (0.72 ) Shares used to compute basic and diluted net loss per share 1,138,911 10,957,150 13,674,568 13,731,519

The Company and Basis of Pres30

The Company and Basis of Presentation (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)segment	Dec. 31, 2015USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit | $	$ 93,662	$ 45,497
Number of operating segments | segment	1

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2016
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 Accoun32

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, 2016	Dec. 31, 2015
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)	2,376,618	1,593,818
Common stock options 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)	2,295,393	1,437,583
Common stock warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	17,331	0
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)	63,894	156,235

Short-Term Investments (Details

Short-Term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 19,253	$ 44,960
Unrealized Gains	1	0
Unrealized Losses	(2)	(8)
Fair Value	19,252	44,952
Certificates of deposit
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		20,000
Unrealized Gains		0
Unrealized Losses		0
Fair Value		20,000
Commercial paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,253	24,960
Unrealized Gains	1	0
Unrealized Losses	(2)	(8)
Fair Value	$ 19,252	$ 24,952

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - Fair value measurements, nonrecurring - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of assets	$ 0	$ 0
Fair value of liabilities	$ 0	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - Fair value measurements, recurring basis - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets:
Total assets at fair value	$ 104,082	$ 107,305
Cash equivalents and money market funds
Assets:
Asset fair value	84,830	12,353
Certificates of deposit included in cash and cash equivalents
Assets:
Asset fair value		50,000
Certificates of deposit included in short-term investments
Assets:
Asset fair value		20,000
Commercial paper
Assets:
Asset fair value	19,252	24,952
LEVEL 1
Assets:
Total assets at fair value	84,830	12,353
LEVEL 1 | Cash equivalents and money market funds
Assets:
Asset fair value	84,830	12,353
LEVEL 1 | Certificates of deposit included in cash and cash equivalents
Assets:
Asset fair value		0
LEVEL 1 | Certificates of deposit included in short-term investments
Assets:
Asset fair value		0
LEVEL 1 | Commercial paper
Assets:
Asset fair value	0	0
LEVEL 2
Assets:
Total assets at fair value	19,252	94,952
LEVEL 2 | Cash equivalents and money market funds
Assets:
Asset fair value	0	0
LEVEL 2 | Certificates of deposit included in cash and cash equivalents
Assets:
Asset fair value		50,000
LEVEL 2 | Certificates of deposit included in short-term investments
Assets:
Asset fair value		20,000
LEVEL 2 | Commercial paper
Assets:
Asset fair value	19,252	24,952
LEVEL 3
Assets:
Total assets at fair value	0	0
LEVEL 3 | Cash equivalents and money market funds
Assets:
Asset fair value	0	0
LEVEL 3 | Certificates of deposit included in cash and cash equivalents
Assets:
Asset fair value		0
LEVEL 3 | Certificates of deposit included in short-term investments
Assets:
Asset fair value		0
LEVEL 3 | Commercial paper
Assets:
Asset fair value	$ 0	$ 0

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,744	$ 2,321
Less accumulated depreciation and amortization	(1,370)	(637)
Total	1,374	1,684
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,771	1,438
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	295	242
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	111	111
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 142	$ 105

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Depreciation and amortization of property and equipment	$ 732	$ 461	$ 179

Debt - Additional Information (

Debt - Additional Information (Details)	Oct. 03, 2016USD ($)payment$ / sharesshares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Debt Instrument [Line Items]
Shares of common stock issued upon exercise of warrant | shares	17,331
Warrants exercise price (in dollars per share) | $ / shares	$ 11.54
Percentage of principal of debt used to calculate number of shares issued by warrant	2.00%
Period of average closing price used to calculate number of shares issued by warrant	30 days
Warrant term	10 years
Amortization of debt issue costs		$ 5,000	$ 22,000	$ 23,000
Term Loan | Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000,000
Extension in interest only payments upon achieving milestone	6 months
Number of payments of principal and interest | payment	30
Number of payments of principal and interest upon achieving milestone | payment	24
Stated interest rate	4.50%	4.75%
Prepayment fee percentage in year one	2.00%
Prepayment fee percentage in year two	1.00%
Term Loan | Loan Agreement | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Term Loan | Term A Loan
Debt Instrument [Line Items]
Debt face amount	$ 10,000,000
Amortization of the fair value of the warrants		$ 17,000
Amortization of debt issue costs		$ 5,000
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, 2016USD ($)
Year ended:
December 31, 2017	$ 0
December 31, 2018	2,667
December 31, 2019	4,000
December 31, 2020	3,333
Total future principal payments due under the Term A Loan	$ 10,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details)	Oct. 13, 2016USD ($)$ / sharesshares	Dec. 31, 2016USD ($)vote_per_shareshares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)
Equity [Abstract]
Preferred stock, shares authorized (in shares)		10,000,000	10,000,000
Preferred stock, shares issued (in shares)		0	0
Preferred stock, shares outstanding (in shares)		0	0
Common stock, shares authorized (in shares)		200,000,000	200,000,000
Number of votes entitlement for each share held | vote_per_share		1
Preferred stock, amount of preferred dividends in arrears or default | $		$ 0
Class of Stock [Line Items]
Net proceeds | $		$ 26,622,000	$ 69,271,000	$ 0
Common Stock
Class of Stock [Line Items]
Issuance of stock (in shares)	2,752,637	2,752,637	4,800,000
Offering price (dollars per share) | $ / shares	$ 10.10
Net proceeds | $	$ 26,600,000	$ 1,000

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	4,024,470	3,451,983
Common stock warrants
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	17,331	0
Stock options issued and outstanding
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	2,295,393	1,437,583
Authorized for future stock awards under the Company's option plans
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	1,404,933	1,788,396
Awards available under the ESPP
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	306,813	226,004

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from exercise of stock options	$ 525	$ 387	$ 749
Weighted average grant date fair values of stock options granted (USD per share)	$ 6.99
Grant date fair value of stock options, vested	$ 3,600
Unrecognized share-based compensation expense of unvested employee stock options	$ 7,800
Unvested stock options, unrecognized cost expected to be recognized (in years)	2 years 1 month 21 days
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	2,376,618	1,593,818
Common stock subject to repurchase
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	63,894	156,235
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)	58,616
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting terms (in years)	4 years
Proceeds from exercise of stock options	$ 144	$ 341
Two Thousand Sixteen Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested stock options, unrecognized cost expected to be recognized (in years)	1 year 10 months 24 days
Unrecognized share-based compensation expense of unvested employee stock options	$ 600
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 under the Company's option plans
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 under the Company's option plans | 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 under the Company's option plans | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting terms (in years)	3 years
Authorized for future stock awards under the Company's option plans | 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 Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Beginning balance (in shares)	1,437,583
Granted (in shares)	947,025
Exercised (in shares)	(83,353)
Canceled (in shares)	(5,862)
Ending balance (in shares)	2,295,393	1,437,583
Weighted Average Exercise Price
Beginning balance (USD per share)	$ 6.19
Granted (USD per share)	10.16
Exercised (USD per share)	6.30
Canceled (USD per share)	5.97
Ending balance (USD per share)	$ 7.82	$ 6.19
Stock Options, Additional Disclosures
Weighted average remaining contractual life, Outstanding	8 years 2 months 12 days	8 years 11 months 9 days
Total aggregate intrinsic value, Outstanding	$ 6,774	$ 15,774
Vested and expected to vest (in shares)	2,295,393
Weighted average exercise price of shares vested and expected to vest (USD per share)	$ 7.82
Weighted average remaining contractual life of shares vested and expected to vest (in years)	8 years 2 months 12 days
Total aggregate intrinsic value of shares vested and expected to vest	$ 6,774
Exercisable (in shares)	878,658
Weighted average exercise price of shares exercisable (USD per share)	$ 7.05
Weighted average remaining contractual life of shares exercisable (in years)	8 years 1 month 24 days
Total aggregate intrinsic value of shares exercisable	$ 3,444

Equity Incentive Plans - Summ44

Equity Incentive Plans - Summary of Black-Scholes Option Pricing Model Assumptions (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum (as a percentage)	0.48%	0.35%
Risk-free interest rate, maximum (as a percentage)	1.08%	0.94%
Expected dividend yield (as a percentage)	0.00%	0.00%
Expected volatility, minimum (as a percentage)	80.00%	65.00%
Expected volatility, maximum (as a percentage)	107.00%	101.00%
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 under the Company's option plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum (as a percentage)	1.14%	1.53%
Risk-free interest rate, maximum (as a percentage)	2.09%	1.91%
Expected dividend yield (as a percentage)	0.00%	0.00%
Expected volatility, minimum (as a percentage)	80.00%	78.00%
Expected volatility, maximum (as a percentage)	82.00%	80.00%
Authorized for future stock awards under the Company's option plans | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years
Authorized for future stock awards under the Company's option plans | 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 - Summ45

Equity Incentive Plans - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 4,344	$ 3,033
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,005	1,586
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,339	$ 1,447

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Contingency [Line Items]
Effective income tax reconciliation at federal statutory rate (as a percent)	34.00%	34.00%	34.00%
Deferred tax assets, valuation allowance	$ 33,451	$ 18,454
Unrecognized tax benefits	4,642	$ 356	$ 108	$ 6
Unrecognized tax benefits that would impact on effective tax rate	3,200
Federal
Income Tax Contingency [Line Items]
Net operating loss carryforwards	79,500
Tax credit carryforwards, research and development	4,300
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards	39,100
Tax credit carryforwards, research and development	$ 900

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, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal income taxes at 34%	$ (16,334)	$ (10,946)	$ (4,044)
State income tax, net of federal benefit	(1)	(1,821)	(672)
Tax effect on nondeductible expenses	1,650	341	132
Research credits	(3,538)	(676)	(265)
Rate change	267	0	0
Change in valuation allowance	14,996	13,084	4,849
Reserve for uncertain tax positions	2,883	0	0
Other	77	18	0
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, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating losses	$ 27,309	$ 15,646
Research credits	3,646	987
Intangibles	466	590
Other	2,030	1,231
Total deferred tax assets	33,451	18,454
Less valuation allowance	(33,451)	(18,454)
Income tax expense	$ 0	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Unrecognized tax benefits
Balance as of the beginning of the year	$ 356	$ 108	$ 6
Increases related to current year tax positions	921	248	102
Increases related to prior year tax positions	3,365	0	0
Balance as of the end of the year	$ 4,642	$ 356	$ 108

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)Option1claim1	Dec. 31, 2015USD ($)
Commitments and Contingencies Disclosure [Abstract]
Number of claims and actions pending | claim1	0
Number of operating lease options for extension | Option1	2
Operating leases renewal term (in years)	2 years
Annual increase in base rent (as a percent)	3.00%
Lease rent expense | $	$ 733	$ 581
Contractual obligation, contract termination notice period	30 days

Commitments and Contingencies51

Commitments and Contingencies - Schedule of Future Minimum Lease Payment (Details) $ in Thousands	Dec. 31, 2016USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 724
2,018	746
Total minimum lease payments	$ 1,470

Selected Quarterly Financial 52

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Operating expenses	$ 14,353	$ 12,336	$ 11,862	$ 9,885	$ 9,928	$ 9,207	$ 6,446	$ 6,732	$ 48,436	$ 32,313	$ 11,623
Other income (expense)	(41)	109	107	96	60	33	32	(5)
Net loss	$ (14,394)	$ (12,227)	$ (11,755)	$ (9,789)	$ (9,868)	$ (9,174)	$ (6,414)	$ (6,737)	$ (48,165)	$ (32,193)	$ (11,894)
Basic and diluted net loss per share (USD per share)	$ (0.88)	$ (0.88)	$ (0.85)	$ (0.71)	$ (0.72)	$ (0.67)	$ (0.59)	$ (5.92)	$ (3.32)	$ (3.25)	$ (14.51)
Shares used to compute basic and diluted net loss per share (in shares)	16,352,046	13,910,145	13,871,938	13,807,825	13,731,519	13,674,568	10,957,150	1,138,911	14,488,987	9,920,382	819,868