Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2016	Mar. 14, 2017	Jun. 30, 2016
Document and Entity Information
Entity Registrant Name	Aclaris Therapeutics, Inc.
Entity Central Index Key	0001557746
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		26,088,866
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	FY
Entity Public Float			$ 156.5

CONSOLIIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 30,171	$ 9,851
Marketable securities	107,051	75,017
Prepaid expenses and other current assets	1,334	1,656
Total current assets	138,556	86,524
Marketable securities	36,912	7,170
Property and equipment, net	481	360
Deferred offering costs	116	0
Other assets	20	22
Total assets	176,085	94,076
Current liabilities:
Accounts payable	2,845	810
Accrued expenses	3,378	745
Total current liabilities	6,223	1,555
Other liabilities	372
Total liabilities	6,595	1,555
Stockholders' Equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized and no shares issued or outstanding at December 31, 2016 and December 31, 2015
Common stock, $0.00001 par value; 100,000,000 shares authorized at December 31, 2016 and December 31, 2015; 26,059,181 and 20,157,503 shares issued and outstanding at December 31, 2016 and December 31, 2015, respectively
Additional paid-in capital	260,671	135,503
Accumulated other comprehensive loss	(269)	(149)
Accumulated deficit	(90,912)	(42,833)
Total stockholders’ equity	169,490	92,521
Total liabilities and stockholders’ equity	$ 176,085	$ 94,076

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Consolidated Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	26,059,181	20,157,503
Common stock, shares outstanding	26,059,181	20,157,503

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	$ 33,476	$ 15,339	$ 6,507
General and administrative	15,091	5,328	2,026
Total operating expenses	48,567	20,667	8,533
Loss from operations	(48,567)	(20,667)	(8,533)
Other income, net	488	104	16
Net loss	(48,079)	(20,563)	(8,517)
Accretion of convertible preferred stock		(2,566)	(2,054)
Net loss attributable to common stockholders	$ (48,079)	$ (23,129)	$ (10,571)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (2.25)	$ (3.79)	$ (6.15)
Weighted average common shares outstanding, basic and diluted (in shares)	21,415,733	6,107,042	1,720,082
Other comprehensive loss:
Unrealized gain (loss) on marketable securities, net of tax of $0	$ 105	$ (148)	$ (9)
Foreign currency translation adjustments	(225)	5
Total other comprehensive loss	(120)	(143)	(9)
Comprehensive loss	$ (48,199)	$ (20,706)	$ (8,526)

CONSOLIDATED STATEMENT OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock Private Placement [Member]	Common Stock Follow On Public Offering [Member]	Common Stock	Additional Paid-In Capital Private Placement [Member]	Additional Paid-In Capital Follow On Public Offering [Member]	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Private Placement [Member]	Follow On Public Offering [Member]	Total
Balance at Dec. 31, 2013											$ 23,000
Balance (in shares) at Dec. 31, 2013											20,890,000
Increase (Decrease) in Temporary Equity
Issuance of convertible preferred stock, net of issuance costs											$ 11,623
Issuance of convertible preferred stock (in shares)											6,451,057
Accretion of convertible preferred stock to redemption value											$ 2,054
Balance at Dec. 31, 2014											$ 36,677
Balance (in shares) at Dec. 31, 2014											27,341,057
Balance at Dec. 31, 2013							$ 3	$ (9,166)			$ (9,163)
Balance (in shares) at Dec. 31, 2013			2,730,427
Increase (Decrease) in Stockholders' Equity
Unrealized gain (loss) on marketable securities, net of tax of $0							(9)				(9)
Equity Impact of Purchase Put Option								(1,039)			(1,039)
Stock-based compensation expense						$ 27					27
Accretion of convertible preferred stock, APIC effect						(27)
Accretion of convertible preferred stock, equity effect								(2,027)			(2,054)
Net loss								(8,517)			(8,517)
Balance at Dec. 31, 2014							(6)	(20,749)			(20,755)
Balance (in shares) at Dec. 31, 2014			2,730,427
Increase (Decrease) in Temporary Equity
Issuance of convertible preferred stock, net of issuance costs											$ 39,864
Issuance of convertible preferred stock (in shares)											12,944,984
Accretion of convertible preferred stock to redemption value											$ 1,764
Issuance of common stock upon conversion of convertible preferred stock											$ (78,305)
Conversion of convertible preferred stock into permanent equity (in shares)											(40,286,041)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock						56,550					$ 56,550
Number of shares issued			5,750,000
Issuance of stock upon conversion						78,305					78,305
Issuance of stock upon conversion, shares			11,677,076
Unrealized gain (loss) on marketable securities, net of tax of $0							(148)				(148)
Foreign currency translation adjustment							5				5
Stock-based compensation expense						891					891
Accretion of convertible preferred stock, APIC effect						(243)
Accretion of convertible preferred stock, equity effect								(1,521)			(1,764)
Net loss								(20,563)			(20,563)
Balance at Dec. 31, 2015						135,503	(149)	(42,833)			$ 92,521
Balance (in shares) at Dec. 31, 2015			20,157,503								20,157,503
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in connection with Vixen acquisition						2,355					$ 2,355
Issuance of common stock in connection with Vixen acquisition, shares			159,420
Issuance of common stock				$ 18,547	$ 98,158				$ 18,547	$ 98,158
Number of shares issued	1,081,082	4,600,000
Exercise of stock options and vesting of RSUs						4					$ 4
Exercise of stock options and vesting of RSUs, shares			61,176								51,980
Unrealized gain (loss) on marketable securities, net of tax of $0							105				$ 105
Foreign currency translation adjustment							(225)				(225)
Stock-based compensation expense						6,104					6,104
Net loss								(48,079)			(48,079)
Balance at Dec. 31, 2016						$ 260,671	$ (269)	$ (90,912)			$ 169,490
Balance (in shares) at Dec. 31, 2016			26,059,181								26,059,181

CONSOLIDATED STATEMENT OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Follow On Public Offering [Member]
Offering costs incurred	$ 6,492
IPO
Offering costs incurred		$ 2,272
Private Placement [Member]
Offering costs incurred	$ 1,453
Series B convertible preferred stock
Temporary equity, issuance costs			$ 60
Series C convertible preferred stock
Temporary equity, issuance costs		$ 136

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (48,079)	$ (20,563)	$ (8,517)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	120	90	12
Stock-based compensation expense	6,104	891	27
Write-down of property and equipment held for sale	216	289
Non-cash charges related to Vixen acquisition	2,784
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(8)	(1,269)	(152)
Accounts payable	1,810	(359)	819
Accrued expenses	2,450	552	175
Net cash used in operating activities	(34,603)	(20,369)	(7,636)
Cash flows from investing activities:
Purchases of property and equipment	(232)	(507)	(417)
Purchases of marketable securities	(148,764)	(82,513)	(5,035)
Proceeds from sales and maturities of marketable securities	87,093	6,069	3,673
Net cash used in investing activities	(61,903)	(76,951)	(1,779)
Cash flows from financing activities:
Proceeds from issuance of common stock in connection with private placement, net of issuance costs	18,547
Proceeds from follow-on public offering, net of issuance costs	98,158
Proceeds from initial public offering, net of offering costs		56,550
Proceeds from issuance of convertible preferred stock, net of issuance costs		39,864	10,584
Proceeds from the exercise of employee stock options	121
Net cash provided by financing activities	116,826	96,414	10,584
Net increase (decrease) in cash and cash equivalents	20,320	(906)	1,169
Cash and cash equivalents at beginning of period	9,851	10,757	9,588
Cash and cash equivalents at end of period	30,171	9,851	10,757
Supplemental disclosures of non-cash investing and financing activities:
Additions to property and equipment included in accounts payable	11	2	91
Fair value of stock issued in connection with Vixen acquisition	2,355
Offering costs included in accounts payable	$ 250
Accretion of convertible preferred stock to redemption value		$ 1,764	2,054
Fair value of preferred stock purchased put option on date of issuance			$ 1,039

Organization and Nature of Business	12 Months Ended
Organization and Nature of Business	Dec. 31, 2016
Organization and Nature of Business
Organization and Nature of Business	1. Organization and Nature of Business Aclaris Therapeutics, Inc. was incorporated under the laws of the State of Delaware in 2012. On July 17, 2015, Aclaris Therapeutics International Limited (“ATIL”) was established under the laws of the United Kingdom as a wholly-owned subsidiary of Aclaris Therapeutics, Inc. On March 24, 2016, Vixen Pharmaceuticals, Inc. (“Vixen”) became a wholly-owned subsidiary of Aclaris Therapeutics, Inc. (see Note 12). Aclaris Therapeutics, Inc., together with ATIL and Vixen, are referred to collectively as the “Company”. The Company is a clinical‑stage biotechnology company focused on identifying, developing and commercializing innovative and differentiated drugs to address significant unmet needs in dermatology. The Company’s lead drug candidate, A-101 40% Topical Solution, is a proprietary high‑concentration formulation of hydrogen peroxide topical solution that the Company is developing as a prescription treatment for seborrheic keratosis (“SK”), a common non‑malignant skin tumor. The Company has completed three Phase 3 clinical trials of A-101 40% Topical Solution in patients with SK, and submitted a New Drug Application (“NDA”) to the U.S. Food and Drug Administration (“FDA”) in February 2017. Initial Public Offering On October 6, 2015, the Company’s registration statement on Form S-1 relating to its initial public offering of its common stock (the “IPO”) was declared effective by the Securities and Exchange Commission (“SEC”). The Company’s common stock began trading on the NASDAQ Global Select Market on October 7, 2015. The IPO closed on October 13, 2015, and 5,000,000 shares of common stock were sold at a price to the public of $11.00 per share, for aggregate gross proceeds of $55,000. In addition, upon the closing of the IPO, all of the Company’s outstanding convertible preferred stock was converted into an aggregate total of 11,677,076 shares of common stock. The conversion of the convertible preferred stock was a non-cash transaction which has been excluded from the Consolidated Statements of Cash Flows. On October 12, 2015, the underwriters of the IPO exercised in full their option to purchase additional shares, and on October 13, 2015, the Company sold 750,000 additional shares of common stock at a price to the public of $11.00 per share, for aggregate gross proceeds of $8,250. The Company paid underwriting discounts and commissions of $4,428 to the underwriters in connection with the IPO, including the underwriters’ exercise of their option to purchase additional shares. In addition, the Company incurred expenses of $2,272 in connection with the IPO. The net offering proceeds received by the Company, after deducting underwriting discounts, commissions and offering expenses, were $56,550. Private Placement On June 2, 2016, pursuant to a securities purchase agreement with certain accredited investors dated May 27, 2016, the Company closed a private placement in which it sold an aggregate of 1,081,082 shares of common stock at a price of $18.50 per share, for gross proceeds of $20,000. The Company incurred placement agent fees of $1,300 and expenses of $153 in connection with the private placement. The net offering proceeds received by the Company, after deducting placement agent fees and transaction expenses, were $18,547. Follow-On Offering On November 13, 2016, the Company’s registration statement on Form S-3 was declared effective by the SEC. On November 17, 2016, the Company entered into an underwriting agreement with representatives of the underwriters, to issue and sell 4,000,000 shares of common stock pursuant to the registration statement filed on Form S-3 (the “Follow-On Offering”). The shares of common stock were sold to the public at a price of $22.75 per share, for gross proceeds of $91,000. On November 17, 2016, the underwriters of the Follow-On Offering exercised in full their option to purchase 600,000 additional shares of common stock at a price to the public of $22.75 per share, for gross proceeds of $13,650. The Company paid underwriting discounts and commissions of $6,279 to the underwriters in connection with the Follow-On Offering, including the underwriters’ exercise of their option to purchase additional shares. In addition, the Company incurred expenses of $188 in connection with the Follow-On Offering. The net offering proceeds received by the Company, after deducting underwriting discounts, commissions and offering expenses, were $98,158. Liquidity The Company’s consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. At December 31, 2016, the Company had cash, cash equivalents and marketable securities of $174,134 and an accumulated deficit of $90,912. The Company has not generated any product revenues and has not achieved profitable operations. There is no assurance that profitable operations will ever be achieved, and, if achieved, will be sustained on a continuing basis. In addition, development activities, clinical and pre-clinical testing, and commercialization of the Company’s drug candidates will require significant additional financing. The Company expects that its cash, cash equivalents and marketable securities as of December 31, 2016, will be sufficient to fund its operations for a period greater than 12 months from the date of issuance of these consolidated financial statements based on its current operating assumptions. The future viability of the Company is dependent on its ability to generate cash from operating activities or to raise additional capital to finance its operations. The Company’s failure to raise capital as and when needed could have a negative impact on its financial condition and ability to pursue its business strategies.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2016

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The financial statements include the consolidated accounts of the Company and its wholly-owned subsidiaries, ATIL and Vixen. All intercompany transactions have been eliminated.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, research and development expenses and the valuation of stock-based awards.

Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expenses include salaries, stock-based compensation and benefits of employees, fees paid under licensing agreements, fees paid under a third party assignment agreement and other operational costs related to the Company’s research and development activities, including depreciation expenses and the cost of research and development contracts which the Company has entered into with outside vendors to conduct both preclinical studies and clinical trials. Significant judgment and estimates are made in determining the amount of research and development costs recognized in each reporting period. The Company analyzes the progress of its preclinical studies and clinical trials, completion of milestone events, invoices received and contracted costs when estimating research and development costs. Actual results could differ from the Company’s estimates. The Company’s historical estimates for research and development costs have not been materially different from the actual costs.

Foreign Currency Translation

The reporting currency of the Company is the U.S. Dollar. The functional currency of ATIL, the Company’s wholly-owned subsidiary, is the British Pound. Assets and liabilities of ATIL are translated into U.S. Dollars based on exchange rates at the end of each reporting period. Revenues and expenses are translated at average exchange rates during the reporting period. Gains and losses arising from the translation of assets and liabilities are included as a component of accumulated other comprehensive loss within the Company’s consolidated balance sheet. Gains and losses resulting from foreign currency transactions are reflected within the Company’s consolidated statements of operations. The Company has not utilized foreign currency hedging strategies to mitigate the effect of its foreign currency exposure.

Stock-Based Compensation

The Company measures the compensation expense of stock-based awards granted to employees and directors using the grant date fair value of the award. The Company has issued stock options and restricted stock unit (“RSU”) awards with service-based vesting conditions, as well as with performance-based vesting conditions. The Company has not issued awards that include market-based conditions. For service-based awards the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. For performance-based awards the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period beginning in the period that it becomes probable the performance conditions will occur. At each balance sheet date, the Company evaluates whether any performance conditions related to a performance-based award have changed. The effect of any change in performance conditions would be recognized as a cumulative catch-up adjustment in the period such change occurs, and any remaining unrecognized compensation expense would be recognized on a straight-line basis over the remaining requisite service period. The impact of forfeitures is recognized in the period in which they occur.

The Company initially measures the compensation expense of stock-based awards granted to consultants using the grant date fair value of the award. Compensation expense is recognized over the period during which services are rendered by such consultants. At the end of each financial reporting period prior to completion of services being rendered, the compensation expense related to these awards is remeasured using the then current fair value of the Company’s common stock for RSUs, or based upon updated assumptions in the Black-Scholes option pricing model for stock option awards.

The Company classifies stock-based compensation expense in its statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified.

The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company estimates its expected stock volatility based on the historical volatility of a set of peer companies, which are publicly traded, and expects to continue to do so until it has adequate historical data regarding the volatility of its own publicly-traded stock price. The expected term of the Company’s stock options has been determined using the “simplified” method for awards that qualify as “plain vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. The Company uses an expected dividend yield of zero based on the fact that the Company has never paid cash dividends and does not expect to pay cash dividends in the future. Prior to the IPO, the Company valued its common stock using a hybrid method to estimate its enterprise value. The hybrid method used was a probability-weighted expected return method which was a scenario-based methodology that estimated the fair value of the Company’s common stock based upon an analysis of future values for the Company assuming various outcomes. The hybrid method used calculated equity values using an option pricing model in one or more of scenarios, and also considered the rights of each class of stock.

The fair value of each RSU is measured using the closing price of the Company’s common stock on the date of grant.

Patent Costs

All patent related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more likely than not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Reverse Stock Split

On September 24, 2015, the Company effected a 1‑for‑3.45 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s then-outstanding convertible preferred stock. Accordingly, all share and per share amounts for all periods presented in these consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios.

Accretion of Convertible Preferred Stock

Accretion of convertible preferred stock included the accretion of accruing dividends on and issuance costs of the Company’s Series A, B and C convertible preferred stock. The carrying values of the Series A and Series B convertible preferred stock were accreted to their respective redemption values, using the effective interest method, from the date of issuance through August 28, 2015. In connection with the closing of the Company’s Series C convertible preferred stock financing on August 28, 2015, the redemption rights of the Series A and B convertible preferred stock were removed. Subsequent to August 28, 2015, the Company was no longer required to record the accumulated undeclared dividends on its balance sheet, but was thereafter required to deduct accumulated undeclared dividends as part of its earnings per share calculation. On October 13, 2015, in connection with the Company’s IPO, all of the Company’s convertible preferred stock was converted to common stock.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. Comprehensive loss is comprised of net loss, foreign currency translation adjustments and unrealized gains (losses) on marketable securities.

Net Loss per Share

Basic net loss per share is computed using the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed using the sum of the weighted average number of common shares outstanding during the period, plus the weighted average number of potential shares of common stock from the assumed exercise of stock options, and the assumed vesting of RSUs and restricted stock granted by the Company upon its formation, if dilutive. Prior to the IPO, the Company applied the two-class method of calculating its basic and diluted net loss per share attributable to common stockholders since its convertible preferred stock and common stock were participating securities. The Company’s convertible preferred stock contractually entitled the holders of such shares to participate in dividends, but not in losses, of the Company. Since the Company was in a net loss position, and preferred stockholders did not participate in losses, basic and diluted net loss per share was the same for each of the periods presented.

Cash Equivalents

The Company considers all short term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which have consisted of money market accounts, commercial paper and corporate debt securities with original maturities of less than three months, are stated at fair value.

Marketable Securities

Marketable securities with original maturities of greater than three months and remaining maturities of less than one year from the balance sheet date are classified as short term. Marketable securities with remaining maturities of greater than one year from the balance sheet date are classified as long term.

The Company classifies all of its marketable securities as available-for-sale securities. The Company’s marketable securities are measured and reported at fair value using quoted prices in markets that are not active for identical or similar securities. Unrealized gains and losses are reported as a separate component of stockholders’ equity (deficit). The cost of securities sold is determined on a specific identification basis, and realized gains and losses, if any, are included in other income, net within the consolidated statement of operations and comprehensive loss. If any adjustment to fair value reflects a decline in the value of the investment, the Company considers available evidence to evaluate the extent to which the decline is “other than temporary” and reduces the investment to fair value through a charge to the statement of operations and comprehensive loss.

Assets Held for Sale

In order for an asset to be classified as held for sale, several criteria must be achieved. These criteria include, among others, an active program to market an asset and locate a buyer, as well as the probable disposition of the asset within one year. Upon being classified as held for sale, the recoverability of the carrying value of an asset must be assessed and evaluated. After the valuation process is completed, the held for sale asset is reported at the lower of its carrying value or fair value less cost to sell, and no additional depreciation expense is recognized related to the asset. Once an asset is classified as held for sale, all of its historical balance sheet information is included in prepaid expenses and other current assets in the accompanying consolidated balance sheets. During the year ended December 31, 2015, the Company determined that several pieces of machinery used in the Company’s scale-up operations would no longer be part of the Company’s future operations. The Company engaged a third-party to market the assets and locate a buyer in the fourth quarter of 2015. During the year ended December 31, 2016, the Company was unable to locate a buyer for the machinery and, therefore, wrote the remaining value of the machinery down to zero. The Company recorded impairment charges of $216 and $289 in the years ended December 31, 2016 and 2015, respectively. The impairment charges are included in research and development expense on the Company’s consolidated statement of operations and comprehensive loss. As of December 31, 2016 and 2015, $0 and $216 in assets were classified as held for sale, respectively.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

Level 1 — Quoted prices in active markets for identical assets or liabilities.

Level 2 — Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above. The carrying value of the Company’s accounts payable and accrued expenses approximate fair value due to the short-term nature of these liabilities.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company holds all cash, cash equivalents and marketable securities balances at one accredited financial institution, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third party manufacturers to supply products for research and development activities of its programs, including preclinical and clinical testing. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and other components.

Deferred Offering Costs

The Company recorded legal, accounting and other third-party fees associated directly with the filing of its registration statement on Form S-3 in November 2016, as deferred offering costs (non-current). These deferred offering costs are recorded in stockholders’ equity as a reduction of the proceeds generated from offerings consummated under the Form S-3 on a pro rata basis. The Company may also record legal, accounting and other third-party fees directly associated with in-process equity financings as deferred offering costs (non-current) until such financings are completed. The deferred costs related to an in-process equity financing are recorded in stockholders’ equity as a reduction of the proceeds generated from the related offering when it is completed. Deferred offering costs of $116 and $0 were recorded as of December 31, 2016 and 2015, respectively.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the useful life of the asset. Computer equipment is depreciated over three years. Manufacturing equipment is depreciated over five years. Furniture and fixtures are depreciated over five years. Leasehold improvements are depreciated over the shorter of the lease term or their useful life. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.

Impairment of Long Lived Assets

Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows.

Segment Data

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is identifying, developing and commercializing innovative and differentiated drugs to address significant unmet needs in dermatology. No revenue has been generated since inception, and all tangible assets are held in the United States.

Recently Issued and Adopted Accounting Pronouncements

In January 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2017-01, Business Combinations-Clarifying the Definition of a Business (Topic 805). The amendments in this ASU provide a screen to determine when a set of acquired assets and/or activities is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired, or disposed of, is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. The amendments in this ASU will reduce the number of transactions that meet the definition of a business. ASU 2017-01 is effective for annual reporting periods beginning after December 15, 2017, including interim periods within those years, and early adoption will be permitted. The Company is assessing the potential impact of ASU 2017-01 on its consolidated financial statements.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326). This ASU introduces a new model for recognizing credit losses on financial instruments based upon estimated expected credit losses. ASU 2016-13 will apply to loans, accounts receivable, financial assets measured at amortized cost and at fair value through other comprehensive income, loan commitments and certain off-balance sheet credit exposures. ASU 2016-13 is effective for annual reporting periods beginning after December 15, 2019, including interim periods within those years, and early adoption will be permitted. The Company is assessing the potential impact of ASU 2016-13 on its consolidated financial statements.

In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting. This ASU requires all tax effects of share-based payment settlements to be recorded through the income statement. Currently, tax benefits in excess of compensation cost, or “windfalls”, are recorded in equity, and tax deficiencies, or “shortfalls”, are recorded to equity to the extent of previous windfalls, and then to the income statement. In addition, under the new guidance, companies will be permitted to make a policy election to recognize the impact of forfeitures either when they occur, or on an estimated basis. Finally, this update simplifies withholding requirements to allow companies to withhold up to an employee’s maximum tax rate without resulting in liability classification for the award. ASU 2016-09 is effective for annual reporting periods beginning after December 15, 2016, and early adoption is permitted. The Company has adopted the provisions of this standard early, the impact of which on its consolidated financial statements was not significant.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). The new standard establishes a right-of-use (“ROU”) model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. ASU 2016-02 is effective for annual periods beginning after December 15, 2018, including interim periods within those annual periods, with early adoption permitted. A modified retrospective transition approach is required for lessees for capital and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. The Company is currently evaluating the potential impact of the adoption of this standard.

In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. The amendments in this update revise the accounting related to the classification and measurement of investments in equity securities and the presentation of certain fair value changes for financial liabilities measured at fair value. The amendments are effective for annual reporting periods beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the potential impact of the adoption of this standard.

In November 2015, the FASB issued ASU 2015- 17, Balance Sheet Classification of Deferred Taxes. The amendments in this update simplify the presentation of deferred income taxes to require that deferred tax liabilities and assets are classified as noncurrent in a statement of financial position. The amendments are effective for annual reporting periods beginning after December 15, 2016 and interim reporting periods within those annual periods. Early application is permitted. The Company has adopted the provisions of this standard early, the impact of which on its consolidated financial statements was not significant.

Fair Value of Financial Assets and Liabilities

12 Months Ended

Dec. 31, 2016

Fair Value of Financial Assets and Liabilities

Fair Value of Financial Assets and Liabilities

3. Fair Value of Financial Assets and Liabilities

The following tables present information about the fair value measurements of the Company’s financial assets and liabilities which are measured at fair value on a recurring basis, and indicate the level of the fair value hierarchy utilized to determine such fair values:


	December 31, 2016
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	11,522	$	12,691	$	—	$	24,213
Marketable securities		—		143,963		—		143,963
Total	$	11,522	$	156,654	$	—	$	168,176


	December 31, 2015
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	8,810	$	250	$	—	$	9,060
Marketable securities		—		82,187		—		82,187
Total	$	8,810	$	82,437	$	—	$	91,247

As of December 31, 2016 and 2015, the Company’s cash equivalents consisted of investments with maturities of less than three months and included a money market fund which was valued based upon Level 1 inputs, and commercial paper and corporate debt securities which were valued based upon Level 2 inputs. In determining the fair value of its Level 2 investments the Company relied on quoted prices for identical securities in markets that are not active. These quoted prices were obtained by the Company with the assistance of a third‑party pricing service based on available trade, bid and other observable market data for identical securities. Quarterly, the Company compares the quoted prices obtained from the third‑party pricing service to other available independent pricing information to validate the reasonableness of the quoted prices provided. The Company evaluates whether adjustments to third-party pricing is necessary and, historically, the Company has not made adjustments to quoted prices obtained from the third-party pricing service third‑party pricing are necessary. During the years ended December 31, 2016 and 2015, there were no transfers between Level 1, Level 2 and Level 3.

As of December 31, 2016 and 2015, the fair value of the Company’s available-for-sale marketable securities by type of security was as follows:


	December 31, 2016
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gain		Loss		Value

Marketable securities:
Corporate debt securities	$	51,352	$	—	$	(59)	$	51,293
Commercial paper		20,463		—		—		20,463
Asset-backed securities		28,692		6		(1)		28,697
U.S. government agency debt securities		43,505		8		(3)		43,510
Total marketable securities	$	144,012	$	14	$	(63)	$	143,963


	December 31, 2015
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gain		Loss		Value
Marketable securities:
Corporate debt securities	$	46,270	$	—	$	(125)	$	46,145
Commercial paper		9,789		—		—		9,789
Asset-backed securities		6,234		—		(14)		6,220
U.S. government agency debt securities		20,048		—		(15)		20,033
Total marketable securities	$	82,341	$	—	$	(154)	$	82,187

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2016

Property and Equipment, Net

Property and Equipment, Net

4. Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
	2016		2015
Computer equipment	$	310	$	262
Manufacturing equipment		149		101
Furniture and fixtures		115		39
Leasehold improvements		33		—
Property and equipment, gross		607		402
Accumulated depreciation		(126)		(42)
Property and equipment, net	$	481	$	360

Depreciation expense was $120, $90 and $12 for the years ended December 31, 2016, 2015 and 2014, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2016

Accrued Expenses

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following:


	December 31,
	2016		2015
Research and development expenses	$	1,166	$	123
Employee compensation expenses		1,732		—
Licensing fees		—		250
Vixen contract payable		100		—
Professional fees		77		283
Other		303		89
Total accrued expenses	$	3,378	$	745

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2016
Stockholders' Equity
Stockholders' Equity	6. Stockholders’ Equity Preferred Stock As of December 31, 2016 and 2015, the Company’s amended and restated certificate of incorporation authorized the Company to issue 10,000,000 shares of undesignated preferred stock. There were no shares of preferred stock outstanding as of December 31, 2016 and 2015. The Company previously issued Series A, Series B and Series C convertible preferred stock (collectively, the “Preferred Stock”). Through August 28, 2015, the Company had issued an aggregate of 11,677,076 shares of Preferred Stock in the Series A, Series B and Series C offerings. Upon the closing of the Company’s IPO in October 2015, all of the then outstanding Preferred Stock was converted into an aggregate total of 11,677,076 shares of common stock. Also in connection with the IPO, the Company amended and restated its certificate of incorporation and authorized 10,000,000 shares of undesignated preferred stock. Common Stock As of December 31, 2016 and 2015, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 100,000,000 shares of $0.00001 par value common stock. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the board of directors, if any, subject to any preferential dividend rights of any series of preferred stock that may be outstanding. No dividends had been declared through December 31, 2016. Restricted Common Stock In July 2012, the Company issued 2,730,427 shares of restricted common stock with time-based vesting to its founders in connection with the formation of the Company. Unvested shares of restricted common stock could not be sold or transferred by the holders of those shares. Of the shares issued in July 2012, 1,918,834 shares were subject to vesting pursuant to restricted stock agreements with 25% vesting in July 2013 and the remaining 75% vesting in equal monthly installments over a three-year period thereafter. Upon the Company’s IPO in October 2015, all remaining unvested shares of restricted common stock vested immediately. The estimated grant‑date fair value of the restricted common stock issued was $0.00001 per share, equal to the par value of each share issued. The aggregate fair value of restricted common stock that vested during the years ended December 31, 2016, 2015 and 2014 was $0, $6,423 and $448, respectively. As of December 31, 2016 and 2015, no shares were subject to repurchase.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 4.E)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21488-112644

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(31))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 4.C)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(d))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23285-112656

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Preferred Stock
-URI http://asc.fasb.org/extlink&oid=6521494

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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Reference 16: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644

+ Details

Stock-Based Awards

12 Months Ended

Dec. 31, 2016

Stock-Based Awards

Stock-Based Awards

7. Stock‑Based Awards

2015 Equity Incentive Plan

On September 15, 2015, the Company’s board of directors adopted the 2015 Equity Incentive Plan (the “2015 Plan”), and on September 16, 2015, the Company’s stockholders approved the 2015 Plan. The 2015 Plan became effective in connection with the Company’s IPO in October 2015. At the time the 2015 Plan became effective, no further grants may be made under the Company’s 2012 Equity Compensation Plan, as amended and restated (the “2012 Plan”). The 2015 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, RSUs, performance stock awards, cash based awards and other stock-based awards. The number of shares initially reserved for the issuance of awards under the 2015 Plan was 1,643,872. The number of shares of common stock that may be issued under the 2015 Plan will automatically increase on January 1 of each year, beginning on January 1, 2016 and ending on January 1, 2025, in an amount equal to the lesser of (i) 4.0% of the shares of the Company’s common stock outstanding on December 31 of the preceding calendar year or (ii) an amount determined by the Company’s board of directors. The shares of common stock underlying any awards that expire, are otherwise terminated, settled in cash or repurchased by the Company under the 2015 Plan and the 2012 Plan will be added back to the shares of common stock available for issuance under the 2015 Plan. As of December 31, 2016, 607,556 shares remained available for grant under the 2015 Plan. As of January 1, 2017, the number of shares of common stock available for issuance under the 2015 Plan was automatically increased by 1,042,367 shares. The 2015 Plan is administered by the Company’s board of directors or, at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock options may not be greater than ten years. The Company has granted stock‑based awards that vest subject to the satisfaction of a service requirement (“service‑based awards”), as well as awards that vest subject to the satisfaction of specific performance-based conditions (“performance-based awards”).

2012 Equity Compensation Plan

Upon the 2015 Plan becoming effective, no further grants can be made under the 2012 Plan. The Company granted a total of 1,140,524 stock options under the 2012 Plan, of which 1,049,667 and 1,140,524 were outstanding as of December 31, 2016, and 2015, respectively. Stock options granted under the 2012 Plan vest over four years and expire after ten years. As required, the exercise price for the stock options granted under the 2012 Plan was not less than the fair value of common shares as determined by the Company as of the date of grant.

Stock Option Valuation

The weighted average assumptions the Company used to estimate the fair value of stock options granted during the years ended December 31, 2016, 2015 and 2014 were as follows:


	Year Ended December 31,
	2016		2015		2014

Risk-free interest rate	2.06	%	1.78	%	1.87	%
Expected term (in years)	6.5		6.3		6.4
Expected volatility	94.86	%	93.90	%	113.90	%
Expected dividend yield	0	%	0	%	0	%

The Company recognizes compensation expense for awards over their vesting period. Compensation expense for awards includes the impact of forfeiture in the period when they occur.

Stock Options

The following table summarizes stock option activity for the years ended December 31, 2016, 2015 and 2014:


					Weighted
			Weighted		Average
			Average		Remaining	Aggregate
	Number		Exercise		Contractual	Intrinsic
	of Shares		Price		Term	Value
					(in years)
Outstanding as of December 31, 2013	—			—	—		—
Granted	500,262		$	1.22
Exercised	—			—
Forfeited and canceled	—			—
Outstanding as of December 31, 2014	500,262			1.22	9.77	$	305
Granted	1,238,262			18.08
Exercised	—			—
Forfeited and canceled	—			—
Outstanding as of December 31, 2015	1,738,524			13.23	9.51		24,722
Granted	1,083,919			27.12
Exercised	(51,980)			2.37
Forfeited and canceled	(68,113)			15.71
Outstanding as of December 31, 2016	2,702,350		$	18.94	9.05	$	24,434
Options vested and expected to vest as of December 31, 2016	2,702,350		$	18.94	9.05	$	24,434
Options exercisable as of December 31, 2016	575,149	(1)	$	10.93	8.42	$	9,512

(1)

All options granted under the 2012 Plan are exercisable immediately, subject to a repurchase right in the Company’s favor that lapses as the option vests. This amount reflects the number of shares under options that were vested, as opposed to exercisable, as of December 31, 2016.

The weighted average grant date fair value of stock options granted during the years ended December 31, 2016, 2015 and 2014 was $21.16, $13.84 and $1.38 per share, respectively.

The intrinsic value of a stock option is calculated as the difference between the exercise price of the stock option and the fair value of the underlying common stock, and cannot be less than zero.

Restricted Stock Units

The following table summarizes RSU activity for the years ended December 31, 2016 and 2015. The Company did not grant RSUs during the year ended December 31, 2014.


		Weighted
		Average
		Grant Date
	Number	Fair Value
	of Shares	Per Share
Outstanding as of December 31, 2014	—		—
Granted	53,800	$	28.68
Vested	—
Forfeited and cancelled	—
Outstanding as of December 31, 2015	53,800		28.68
Granted	180,764		27.16
Vested	(12,950)		28.68
Forfeited and cancelled	(2,000)		28.68
Outstanding as of December 31, 2016	219,614	$	27.43

Stock‑Based Compensation

The following table summarizes stock-based compensation expense recorded by the Company for the years ended December 31, 2016, 2015 and 2014:



	Year Ended December 31,
	2016		2015		2014
Research and development	$	2,291	$	257	$	10
General and administrative		3,813		634		17
	$	6,104	$	891	$	27

As of December 31, 2016, the Company had unrecognized stock‑based compensation expense for stock options and RSUs of $34,349 and $5,790, respectively, which is expected to be recognized over weighted average periods of 3.49 years and 2.83 years, respectively.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Net Loss per Share

12 Months Ended

Dec. 31, 2016

Net Loss per Share

Net Loss per Share

8. Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:


	Year Ended
	December 31,
	2016		2015		2014
Numerator:
Net loss	$	(48,079)	$	(20,563)	$	(8,517)
Accretion of redeemable convertible preferred stock		—		(2,566)		(2,054)
Net loss attributable to common stockholders	$	(48,079)	$	(23,129)	$	(10,571)
Denominator:
Weighted average shares of common stock outstanding		21,415,733		6,637,678		2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding		—		(530,636)		(1,010,345)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted		21,415,733		6,107,042		1,720,082
Net loss per share attributable to common stockholders, basic and diluted	$	(2.25)	$	(3.79)	$	(6.15)

To calculate net loss attributable to common stockholders the Company reduced the net loss for the accretion of issuance costs and cumulative dividends accrued but not paid through August 28, 2015, and the remaining cumulative dividends accrued but not paid through October 13, 2015, the date on which all convertible preferred stock converted to common stock.

The Company’s potential dilutive securities, which included stock options, RSUs, preferred stock, and shares of restricted common stock that were issued but not yet vested, have been excluded from the computation of diluted net loss per share since the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following table presents potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders for the years ended December 31, 2016, 2015 and 2014. All share amounts presented in the table below represent the total number outstanding as of December 31.


	2016	2015	2014

Stock options to purchase common stock	2,702,350	1,738,524	500,262
Restricted stock unit awards	219,614	53,800	—
Unvested restricted common stock	—	—	759,538
Convertible preferred stock (as converted to common stock)	—	—	7,924,919
	2,921,964	1,792,324	9,184,719

Commitments and Contingencies

12 Months Ended

Dec. 31, 2016

Commitments and Contingencies

Commitments and Contingencies

9. Commitments and Contingencies

Agreements for Office Space

In August 2013, the Company entered into a sublease agreement for its office space with related parties (see Note 11), with a term ending on November 30, 2016. As part of an amendment to the sublease agreement entered into in December 2014, the Company increased the amount of office space to be subleased and agreed to new monthly sublease terms commencing in January 2015. On August 14, 2015, the Company further amended its sublease agreement to increase the square footage of the space and to extend the term of the sublease to November 2019. Effective December 1, 2015, the Company further amended its sublease agreement to increase the square footage and agreed to new monthly sublease terms.

In November 2016, the Company entered into a lease agreement with a third-party for additional office space in the same building as its headquarters with a term beginning in February 2017, and ending in November 2019.

Rent expense was $254, $119 and $66 for the years ended December 31, 2016, 2015 and 2014, respectively. The Company recognizes rent expense on a straight-line basis over the term of the agreement and has accrued for rent expense incurred but not yet paid.

As of December 31, 2016, future minimum lease payments under the sublease were as follows:


Year Ending December 31,
2017	$	350
2018		363
2019		339
2020		—
2021		—
Total	$	1,052

Stock Purchase Agreement with Vixen Pharmaceuticals, Inc

Pursuant to the stock purchase agreement with Vixen the Company is obligated to make annual payments of $100 on March 24th of each year, through March 24, 2022, with such amounts being creditable against specified future payments.

License and Collaboration Agreement with JAKPharm LLC and Key Organics, LTD

Pursuant to a commercial license agreement with JAKPharm LLC (“JAKPharm”) and Key Organics, LTD (“Key Organics” and collectively, “Licensors”) for the development and commercialization of products containing specified compounds developed by the Licensors, the Company is obligated to make annual maintenance payments of $50 per year, which will be creditable against any payments made in such calendar year.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2016 or 2015.

Supply Agreement

In January 2015, the Company executed a clinical and commercial supply agreement with a third party for the manufacture and assembly of certain components for the product applicator that the Company used to dispense A-101 40% Topical Solution in Phase 3 clinical trials, and intends to use for the commercial drug product. The agreement has a term of three years and automatically renews for consecutive one-year terms. If the agreement is terminated by the Company without cause or by the third party for cause prior to the FDA’s approval of A-101 40% Topical Solution, the Company will owe a termination fee equal to $375. If the agreement is terminated by the Company without cause or by the third party for cause after the FDA approval of A-101 40% Topical Solution, the Company will owe a termination fee equal to $275. The Company’s obligation to pay the termination fee expires after the third anniversary date of the FDA’s approval of A-101 40% Topical Solution.

Income Taxes

12 Months Ended

Dec. 31, 2016

Income Taxes

Income Taxes

10. Income Taxes

During the years ended December 31, 2016, 2015 and 2014, the Company recorded no income tax benefits for the net operating losses incurred in each year, due to its uncertainty of realizing a benefit from those items.

Loss before income taxes is allocated as follows:


	Year Ended December 31,
	2016		2015		2014
U.S. operations	$	(40,597)	$	(11,823)	$	(8,517)
Foreign operations		(7,482)		(8,740)		—
Loss before income taxes	$	(48,079)	$	(20,563)	$	(8,517)

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended December 31,
	2016		2015		2014
Federal statutory income tax rate	(34.0)	%	(34.0)	%	(34.0)	%
State taxes, net of federal benefit	(5.2)		(3.8)		(6.6)
Foreign rate differential	3.2		6.0		—
Permanent differences	1.8		—		—
Research and development tax credits	(2.0)		(1.5)		(1.0)
Change in deferred tax asset valuation allowance	36.2		33.3		41.6
Effective income tax rate	—	%	—	%	—	%

Net deferred tax assets as of December 31, 2016 and 2015 consisted of the following:


		December 31,
	2016		2015
Deferred tax assets:
Net operating loss carryforwards	$	16,836	$	5,750
Capitalized start up costs		8,840		4,401
Research and development tax credit carryforwards		1,480		500
Capitalized research and development expenses		594		611
Intangible asset		1,403		1,650
Stock‑based compensation expenses		2,629		373
Property and equipment		199		—
Other		2		1
Total deferred tax assets		31,983		13,286
Deferred tax liabilities:
Section 481(a) adjustment		(1,257)		—
Other		—		—
Total deferred tax liabilities		(1,257)		—
Valuation allowance		(30,726)		(13,286)
Net deferred tax assets	$	—	$	—

As of December 31, 2016, the Company had federal and state net operating loss carryforwards of $38,137 for each, which begin to expire in 2032. As of December 31, 2016, the Company also had federal and state research and development tax credit carryforwards of $1,488, which begin to expire in 2032. The Company also has $7,972 of loss carry forwards in the United Kingdom, which can be carried forward indefinitely. Utilization of the net operating loss carryforwards and research and development tax credit carryforwards in the United States may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that may have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long term tax exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of December 31, 2016 and 2015. Management reevaluates the positive and negative evidence at each reporting period.

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2016, 2015, and 2014 related primarily to the increases in net operating loss carryforwards, capitalized start-up costs, and research and development tax credit carryforwards and were as follows:


		Year Ended December 31,
		2016		2015		2014
Valuation allowance at beginning of year	$	(13,286)	$	(6,444)	$	(2,899)
Decreases recorded as benefit to income tax provision		—		—		—
Increases recorded to income tax provision		(17,440)		(6,842)		(3,545)
Valuation allowance as of end of year	$	(30,726)	$	(13,286)	$	(6,444)

During the year ended December 31, 2015, the Company recorded unrecognized tax benefits in the amount of $4,440 related to start-up costs that were previously deducted beginning in the initial return filing period ended December 31, 2012. During the year ended December 31, 2016, the Company filed a method of accounting change with the IRS related to the start-up costs, and reversed the related unrecognized tax position. The following table summarizes the changes in the Company’s unrecognized tax benefits:


	Year ended December 31,
	2016		2015		2014
Unrecognized tax benefits at beginning of year	$	(4,400)	$	—	$	—
Increases related to prior year tax provisions				(2,624)		—
Decreases related to prior year tax provisions		4,400		—		—
Increases related to current year tax provisions				(1,776)		—
Unrecognized tax benefits as of end of year	$	—	$	(4,400)	$	—

The total amount of unrecognized tax benefits that, if recognized, would impact the Company’s effective tax rate were $0 as of both December 31, 2016 and 2015. The Company accrues interest and penalties related to unrecognized tax benefits in income tax expense in the consolidated statements of operations and comprehensive loss. During each of the years ended December 31, 2016, 2015 and 2014, the Company recognized expense/(benefit) of $0 related to interest and penalties.

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 federal and state jurisdictions, where applicable. There are currently no pending income tax examinations. The Company’s tax years are still open under statute from 2012 to the present. All open years may be examined to the extent that tax credit or net operating loss carryforwards are used in future periods. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision.

Related Party Transactions

12 Months Ended

Dec. 31, 2016

Related Party Transactions

Related Party Transactions

11. Related Party Transactions

In August 2013, the Company entered into a sublease agreement with NeXeption, Inc. (“NeXeption”), which was subsequently amended in December 2014, August 2015 and October 2016. In August 2015, pursuant to an Assignment and Assumption Agreement, NeXeption assigned all interests, rights, duties and obligations under the sublease to NST Consulting, LLC, a wholly-owned subsidiary of NST, LLC. Mr. Stephen Tullman, the chairman of the Company’s board of directors, was an executive officer of NeXeption and is also the manager of NST Consulting, LLC and NST, LLC. Total payments made under the sublease during the years ended December 31, 2016, 2015 and 2014, were $387, $124 and $66, respectively.

In February 2014, the Company entered into a services agreement with NST, LLC (the “NST Services Agreement”), pursuant to which NST, LLC provided certain pharmaceutical development, management and other administrative services to the Company. Under the same agreement, the Company also provided services to another company under common control with the Company and NST, LLC and was reimbursed by NST, LLC for those services. In addition to Mr. Tullman’s role as manager of NST, LLC, several of the Company’s executive officers are members of NST, LLC.

The NST Services Agreement was amended in January 2015 pursuant to which NST, LLC assigned all interests, rights, duties and obligations under the NST Services Agreement to NST Consulting, LLC. Under the NST Services Agreement, as amended, NST Consulting, LLC provides services to the Company and the Company provides services to another company under common control with the Company and NST Consulting, LLC. The NST Services Agreement was further amended in August 2015, November 2015 and December 2016 to adjust the amount of services the Company is obligated to provide to NST Consulting, LLC and the amount of services NST Consulting, LLC is obligated to provide to the Company. The Company may offset any payments owed by the Company to NST Consulting, LLC against payments that are owed by NST Consulting, LLC to the Company for the provision of personnel, including consultants, to the Company.

During the years ended December 31, 2016, 2015 and 2014 amounts included in the consolidated statement of operations for the NST Services Agreement are summarized in the following table:


	Year Ended
	December 31,
	2016		2015		2014
Services provided by NST Consulting, LLC	$	323	$	455	$	467
Services provided to NST Consulting, LLC		(56)		(294)		(158)
General and administrative expense, net	$	267	$	161	$	309

Services provided by NST Consulting, LLC	$	246	$	52	$	—
Services provided to NST Consulting, LLC		(97)		(259)		(255)
Research and development expense, net	$	149	$	(207)	$	(255)

Services provided by NST Consulting, LLC	$	569	$	507	$	467
Services provided to NST Consulting, LLC		(153)		(553)		(413)
Total, net	$	416	$	(46)	$	54


Net payments made to (received from) NST	$	325	$	(46)	$	54

The Company had $91 and $0 payable to NST Consulting, LLC under the NST Services Agreement as of December 31, 2016, and December 31, 2015, respectively.

Agreements Related to Intellectual Property	12 Months Ended
Agreements Related to Intellectual Property	Dec. 31, 2016
Agreements Related to Intellectual Property
Agreements Related to Intellectual Property	12. Agreements Related to Intellectual Property Assignment Agreement and Finder’s Services Agreement In August 2012, the Company entered into an assignment agreement with the Estate of Mickey Miller (the “Miller Estate”) under which the Company acquired some of the intellectual property rights covering A-101. The assignment of intellectual property rights covers specified know-how, along with modifications of, improvements to and variations on A-101 that meet defined chemical properties. Under the agreement, the Company has the sole and exclusive right, but not the duty, to develop, obtain regulatory approval for and commercialize A-101 in various countries throughout the world. The Company is required to use commercially reasonable efforts to develop and commercialize at least one product for at least one indication in the United States. In connection with obtaining the assignment of the intellectual property from the Miller Estate, the Company also entered into a separate finder’s services agreement with KPT Consulting, LLC. Under the terms of the assignment agreement and the finder’s services agreement, the Company made one-time milestone payments of $400 in 2013 upon the dosing of the first human subject with A-101 40% Topical Solution in the Company’s Phase 2 clinical trial. There are no remaining potential milestone payments under the assignment agreement. Under the finder’s services agreement, the Company made a one-time milestone payment of $300 in the year ended December 31, 2016 upon the dosing of the first human subject with A-101 40% Topical Solution in the Company’s Phase 3 clinical trial and is obligated to make additional milestone payments of up to $1,000 in the aggregate upon the achievement of specified development and regulatory milestones and up to $4,500 upon the achievement of specified commercial milestones. The Company recorded the $300 milestone payment as general and administrative expense in the year ended December 31, 2016. Under each of the assignment agreement and the finder’s services agreement, the Company is also obligated to pay royalties on sales of A-101 or related products, at low single-digit percentages of net sales, subject to reduction in specified circumstances. The Company has not made any royalty payments to date under either agreement. Both agreements will terminate upon the expiration of the last pending, viable patent claim of the patents acquired under the assignment agreement, but no sooner than 15 years from the effective date of the agreements. License Agreement with Rigel Pharmaceuticals, Inc. In August 2015, the Company entered into an exclusive, worldwide license and collaboration agreement with Rigel Pharmaceuticals, Inc. (“Rigel”) for the development and commercialization of products containing specified JAK inhibitors developed by Rigel. Under this agreement, the Company intends to develop these JAK inhibitors for the treatment of alopecia areata and potentially for other dermatological conditions. During the year ended December 31, 2015, the Company made an upfront non-refundable payment of $8,000 to Rigel. In addition, the Company has agreed to make aggregate payments of up to $80,000 upon the achievement of specified pre‑commercialization milestones, such as clinical trials and regulatory approvals. Further, the Company has agreed to pay up to an additional $10,000 to Rigel upon the achievement of a second set of development milestones. With respect to any products the Company commercializes under the agreement, the Company will pay Rigel quarterly tiered royalties on its annual net sales of each product at a high single‑digit percentage of annual net sales, subject to specified reductions, until the date that all of the patent rights for that product have expired, as determined on a country‑by‑country and product‑by‑product basis or, in specified countries under specified circumstances, ten years from the first commercial sale of such product. The agreement terminates on the date of expiration of all royalty obligations unless earlier terminated by either party for a material breach. The Company may also terminate the agreement without cause at any time upon advance written notice to Rigel. Rigel, after consultation with the Company, will be responsible for maintaining and prosecuting the patent rights, and the Company will have final decision making authority regarding such patent rights for a product in the United States and the European Union. To the extent that the Company and Rigel jointly develop intellectual property, the parties will confer and decide which party will be responsible for filing, prosecuting and maintaining those patent rights. The agreement also establishes a joint steering committee composed of an equal number of representatives for each party which will monitor progress in the development of products. The Company accounted for the transaction as an asset acquisition as the licensing arrangement did not meet the definition of a business pursuant to the guidance prescribed in ASC Topic 805, Business Combinations. Accordingly, the Company recorded the $8,000 upfront payment as research and development expense in the year ended December 31, 2015. The Company will record as expense any contingent milestone payments or royalties in the period in which such liabilities are incurred. The Company concluded that licensing arrangement with Rigel did not meet the definition of a business because the transaction principally resulted in its acquisition of intellectual property. As part of the transaction, the Company did not acquire any employees or tangible assets, or any processes, protocols or operating systems. In addition, at the time of the acquisition, there were no activities being conducted related to the licensed patents. The Company will expense the acquired intellectual property asset as of the acquisition date on the basis that costs of intangible assets that are purchased from others for use in research and development activities and that have no alternative future uses are research and development costs at the time the costs are incurred. License and Collaboration Agreement with JAKPharm LLC and Key Organics, LTD In November 2015, the Company entered into a commercial license agreement with JAKPharm and Key Organics for the development and commercialization of products containing specified compounds developed by the Licensors. During the year ended December 31, 2015, the Company expensed an upfront non-refundable payment of $250 to the Licensors. The Company will also make annual maintenance payments of $50 per year, which will be creditable against any payments made in such calendar year. In addition, the Company has agreed to make aggregate payments of up to $2,350 upon specified pre‑commercialization milestones, such as clinical trials and regulatory approvals. With respect to any products the Company commercializes under the agreement, the Company will pay the Licensors royalties on its annual net sales of each product at a low single‑digit percentage of annual net sales, until the date that all of the patent rights for that product have expired, as determined on a country-by-country and licensed product-by-licensed product basis or, in specified countries under specified circumstances, ten years from the first commercial sale of such product. The Company may terminate the agreement without cause with three months written notice to the Licensors. The Company accounted for the transaction as an asset acquisition as the licensing arrangement did not meet the definition of a business pursuant to the guidance prescribed in ASC Topic 805, Business Combinations. Accordingly, the Company recorded the $250 upfront payment as research and development expense in the year ended December 31, 2015. The Company will record as expense any contingent milestone payments or royalties in the period in which such liabilities are incurred. The Company concluded that licensing arrangement with the Licensors did not meet the definition of a business because the transaction principally resulted in its acquisition of intellectual property. As part of the transaction, the Company did not acquire any employees or tangible assets, or any processes, protocols or operating systems. In addition, at the time of the acquisition, there were no activities being conducted related to the licensed patents. The Company will expense the acquired intellectual property asset as of the acquisition date on the basis that costs of intangible assets that are purchased from others for use in research and development activities and that have no alternative future uses are research and development costs at the time the costs are incurred. Stock Purchase Agreement with Vixen Pharmaceuticals, Inc. and License Agreement with Columbia University On March 24, 2016, the Company entered into a stock purchase agreement (the “Vixen Agreement”) with Vixen, JAK1, LLC, JAK2, LLC and JAK3, LLC (all together with Vixen, the “Selling Stockholders”) and Shareholder Representative Services LLC, a Colorado limited liability company, solely in its capacity as the representative of the Selling Stockholders. Pursuant to the Vixen Agreement, the Company acquired all shares of Vixen’s capital stock from the Selling Stockholders (the “Vixen Acquisition”). Following the Vixen Acquisition, Vixen became a wholly-owned subsidiary of the Company. Pursuant to the Vixen Agreement, the Company paid $600 upfront and issued an aggregate of 159,420 shares of the Company’s common stock to the Selling Stockholders. The Company is obligated to make annual payments of $100 on March 24th of each year, through March 24, 2022, with such amounts being creditable against specified future payments that may be paid under the Vixen Agreement. The Company is obligated to make aggregate payments of up to $18,000 to the Selling Stockholders upon the achievement of specified pre-commercialization milestones for three products in the United States, the European Union and Japan, and aggregate payments of up to $22,500 upon the achievement of specified commercial milestones. With respect to any commercialized products covered by the Vixen Agreement, the Company is obligated to pay low single-digit royalties on net sales, subject to specified reductions, limitations and other adjustments, until the date that all of the patent rights for that product have expired, as determined on a country-by-country and product-by-product basis or, in specified circumstances, ten years from the first commercial sale of such product. If the Company sublicenses any of Vixen’s patent rights and know-how acquired pursuant to the Vixen Agreement, the Company will be obligated to pay a portion of any consideration the Company receives from such sublicenses in specified circumstances. As a result of the transaction with Vixen, the Company became party to the Exclusive License Agreement, by and between Vixen and the Trustees of Columbia University in the City of New York (“Columbia”), dated as of December 31, 2015 (the “License Agreement”). Under the License Agreement, the Company is obligated to pay Columbia an annual license fee of $10, subject to specified adjustments for patent expenses incurred by Columbia and creditable against any royalties that may be paid under the License Agreement. The Company is also obligated to pay up to an aggregate of $11,600 upon the achievement of specified commercial milestones, including specified levels of net sales of products covered by Columbia patent rights and/or know-how, and royalties at a sub-single-digit percentage of annual net sales of products covered by Columbia patent rights and/or know-how, subject to specified adjustments. If the Company sublicenses any of Columbia’s patent rights and know-how acquired pursuant to the License Agreement, it will be obligated to pay Columbia a portion of any consideration received from such sublicenses in specified circumstances. The royalties, as determined on a country-by-country and product-by-product basis, are payable until the date that all of the patent rights for that product have expired, the expiration of any market exclusivity period granted by a regulatory body or, in specified circumstances, ten years from the first commercial sale of such product. The License Agreement terminates on the date of expiration of all royalty obligations thereunder unless earlier terminated by either party for a material breach, subject to a specified cure period. The Company may also terminate the License Agreement without cause at any time upon advance written notice to Columbia. The Company accounted for the transaction with Vixen as an asset acquisition as the arrangement did not meet the definition of a business pursuant to the guidance prescribed in ASC Topic 805, Business Combinations. The Company concluded the transaction with Vixen did not meet the definition of a business because the transaction principally resulted in the acquisition of the License Agreement. The Company did not acquire tangible assets, processes, protocols or operating systems. In addition, at the time of the transaction, there were no activities being conducted related to the licensed patents. The Company expensed the acquired intellectual property as of the acquisition date on the basis that the cost of intangible assets purchased from others for use in research and development activities, and that have no alternative future uses, are expensed at the time the costs are incurred. Accordingly, the Company recorded the $600 upfront payment, the fair value of the shares of common stock issued of $2,355, and the present value of the six non-contingent annual payments as research and development expense in the year ended December 31, 2016. Additionally, the Company will record as expense any contingent milestone payments or royalties in the period in which such liabilities are incurred.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2016
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
401(k) Savings Plan	13. 401(k) Savings Plan The Company has a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Company contributions to the plan may be made at the discretion of the Company’s board of directors. The Company has elected to match 100% of employee contributions to the 401(k) Plan up to 4% of the employee’s earnings, subject to certain limitations. Company contributions under the 401(k) Plan were $176, $99 and $60 for the years ended December 31, 2016, 2015 and 2014, respectively.

Quarterly Financial Information (unaudited)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information [Text Block]

14. Quarterly Financial Information (unaudited)

This table summarizes the unaudited consolidated financial results of operations for the quarters ended:


	March 31,		June 30,		September 30,		December 31,
2016 Quarter Ended
Revenue	$	—	$	—	$	—	$	—
Operating expenses		13,139		12,989		10,812		11,627
Other income, net		100		118		118		152
Net loss		(13,039)		(12,871)		(10,694)		(11,475)
Net loss attributable to common stockholders	$	(13,039)	$	(12,871)	$	(10,694)	$	(11,475)
Net loss per share attributable to common stockholders, basic and diluted	$	(0.65)	$	(0.62)	$	(0.50)	$	(0.49)

2015 Quarter Ended
Revenue	$	—	$	—	$	—	$	—
Operating expenses		2,629		2,596		10,640		4,802
Other income, net		6		2		7		89
Net loss		(2,623)		(2,594)		(10,632)		(4,714)
Net loss attributable to common stockholders	$	(3,280)	$	(3,270)	$	(11,652)	$	(4,927)
Net loss per share attributable to common stockholders, basic and diluted	$	(1.61)	$	(1.52)	$	(5.12)	$	(0.28)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2016

Summary of Significant Accounting Policies

Basis of Presentation

Use of Estimates

Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Research and Development Costs

Foreign Currency Translation

Stock-Based Compensation

The fair value of each RSU is measured using the closing price of the Company’s common stock on the date of grant.

Patent Costs

Income Taxes

Reverse Stock Split

Accretion of Convertible Preferred Stock

Comprehensive Loss

Net Loss per Share

Cash Equivalents

Marketable Securities

Assets Held for Sale

Fair Value Measurements

Level 1 — Quoted prices in active markets for identical assets or liabilities.

Concentration of Credit Risk and of Significant Suppliers

Deferred Offering costs

Deferred Offering Costs

Property and Equipment

Impairment of Long-Lived Assets

Impairment of Long Lived Assets

Segment Data

Recently Issued and Adopted Accounting Pronouncements

Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2016

Fair Value of Financial Assets and Liabilities

Schedule of assets and liabilities measured at fair value on a recurring basis


	December 31, 2016
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	11,522	$	12,691	$	—	$	24,213
Marketable securities		—		143,963		—		143,963
Total	$	11,522	$	156,654	$	—	$	168,176


	December 31, 2015
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	8,810	$	250	$	—	$	9,060
Marketable securities		—		82,187		—		82,187
Total	$	8,810	$	82,437	$	—	$	91,247

Schedule of the fair value of available for sale marketable securities by type of security


	December 31, 2016
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gain		Loss		Value

Marketable securities:
Corporate debt securities	$	51,352	$	—	$	(59)	$	51,293
Commercial paper		20,463		—		—		20,463
Asset-backed securities		28,692		6		(1)		28,697
U.S. government agency debt securities		43,505		8		(3)		43,510
Total marketable securities	$	144,012	$	14	$	(63)	$	143,963


	December 31, 2015
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gain		Loss		Value
Marketable securities:
Corporate debt securities	$	46,270	$	—	$	(125)	$	46,145
Commercial paper		9,789		—		—		9,789
Asset-backed securities		6,234		—		(14)		6,220
U.S. government agency debt securities		20,048		—		(15)		20,033
Total marketable securities	$	82,341	$	—	$	(154)	$	82,187

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2016

Property and Equipment, Net

Schedule of property and equipment, net


	December 31,
	2016		2015
Computer equipment	$	310	$	262
Manufacturing equipment		149		101
Furniture and fixtures		115		39
Leasehold improvements		33		—
Property and equipment, gross		607		402
Accumulated depreciation		(126)		(42)
Property and equipment, net	$	481	$	360

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2016

Accrued Expenses

Schedule of accrued expenses


	December 31,
	2016		2015
Research and development expenses	$	1,166	$	123
Employee compensation expenses		1,732		—
Licensing fees		—		250
Vixen contract payable		100		—
Professional fees		77		283
Other		303		89
Total accrued expenses	$	3,378	$	745

Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2016

Stock-Based Awards

Assumptions used to determine fair value of stock options granted


	Year Ended December 31,
	2016		2015		2014

Risk-free interest rate	2.06	%	1.78	%	1.87	%
Expected term (in years)	6.5		6.3		6.4
Expected volatility	94.86	%	93.90	%	113.90	%
Expected dividend yield	0	%	0	%	0	%

Summary of stock option activity


					Weighted
			Weighted		Average
			Average		Remaining	Aggregate
	Number		Exercise		Contractual	Intrinsic
	of Shares		Price		Term	Value
					(in years)
Outstanding as of December 31, 2013	—			—	—		—
Granted	500,262		$	1.22
Exercised	—			—
Forfeited and canceled	—			—
Outstanding as of December 31, 2014	500,262			1.22	9.77	$	305
Granted	1,238,262			18.08
Exercised	—			—
Forfeited and canceled	—			—
Outstanding as of December 31, 2015	1,738,524			13.23	9.51		24,722
Granted	1,083,919			27.12
Exercised	(51,980)			2.37
Forfeited and canceled	(68,113)			15.71
Outstanding as of December 31, 2016	2,702,350		$	18.94	9.05	$	24,434
Options vested and expected to vest as of December 31, 2016	2,702,350		$	18.94	9.05	$	24,434
Options exercisable as of December 31, 2016	575,149	(1)	$	10.93	8.42	$	9,512

(1)

Summary of restricted stock activity


		Weighted
		Average
		Grant Date
	Number	Fair Value
	of Shares	Per Share
Outstanding as of December 31, 2014	—		—
Granted	53,800	$	28.68
Vested	—
Forfeited and cancelled	—
Outstanding as of December 31, 2015	53,800		28.68
Granted	180,764		27.16
Vested	(12,950)		28.68
Forfeited and cancelled	(2,000)		28.68
Outstanding as of December 31, 2016	219,614	$	27.43

Stock-based compensation expense



	Year Ended December 31,
	2016		2015		2014
Research and development	$	2,291	$	257	$	10
General and administrative		3,813		634		17
	$	6,104	$	891	$	27

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2016

Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders


	Year Ended
	December 31,
	2016		2015		2014
Numerator:
Net loss	$	(48,079)	$	(20,563)	$	(8,517)
Accretion of redeemable convertible preferred stock		—		(2,566)		(2,054)
Net loss attributable to common stockholders	$	(48,079)	$	(23,129)	$	(10,571)
Denominator:
Weighted average shares of common stock outstanding		21,415,733		6,637,678		2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding		—		(530,636)		(1,010,345)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted		21,415,733		6,107,042		1,720,082
Net loss per share attributable to common stockholders, basic and diluted	$	(2.25)	$	(3.79)	$	(6.15)

Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders


	2016	2015	2014

Stock options to purchase common stock	2,702,350	1,738,524	500,262
Restricted stock unit awards	219,614	53,800	—
Unvested restricted common stock	—	—	759,538
Convertible preferred stock (as converted to common stock)	—	—	7,924,919
	2,921,964	1,792,324	9,184,719

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2016

Commitments and Contingencies

Schedule of future minimum lease payments under the sublease


Year Ending December 31,
2017	$	350
2018		363
2019		339
2020		—
2021		—
Total	$	1,052

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Taxes

Schedule of loss before income taxes by jurisdiction


	Year Ended December 31,
	2016		2015		2014
U.S. operations	$	(40,597)	$	(11,823)	$	(8,517)
Foreign operations		(7,482)		(8,740)		—
Loss before income taxes	$	(48,079)	$	(20,563)	$	(8,517)

Reconciliation of statutory to effective rate


	Year Ended December 31,
	2016		2015		2014
Federal statutory income tax rate	(34.0)	%	(34.0)	%	(34.0)	%
State taxes, net of federal benefit	(5.2)		(3.8)		(6.6)
Foreign rate differential	3.2		6.0		—
Permanent differences	1.8		—		—
Research and development tax credits	(2.0)		(1.5)		(1.0)
Change in deferred tax asset valuation allowance	36.2		33.3		41.6
Effective income tax rate	—	%	—	%	—	%

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]


		December 31,
	2016		2015
Deferred tax assets:
Net operating loss carryforwards	$	16,836	$	5,750
Capitalized start up costs		8,840		4,401
Research and development tax credit carryforwards		1,480		500
Capitalized research and development expenses		594		611
Intangible asset		1,403		1,650
Stock‑based compensation expenses		2,629		373
Property and equipment		199		—
Other		2		1
Total deferred tax assets		31,983		13,286
Deferred tax liabilities:
Section 481(a) adjustment		(1,257)		—
Other		—		—
Total deferred tax liabilities		(1,257)		—
Valuation allowance		(30,726)		(13,286)
Net deferred tax assets	$	—	$	—

Changes in deferred tax asset valuation allowance


		Year Ended December 31,
		2016		2015		2014
Valuation allowance at beginning of year	$	(13,286)	$	(6,444)	$	(2,899)
Decreases recorded as benefit to income tax provision		—		—		—
Increases recorded to income tax provision		(17,440)		(6,842)		(3,545)
Valuation allowance as of end of year	$	(30,726)	$	(13,286)	$	(6,444)

Schedule of Changes in Unrecognized Tax Benefits


	Year ended December 31,
	2016		2015		2014
Unrecognized tax benefits at beginning of year	$	(4,400)	$	—	$	—
Increases related to prior year tax provisions				(2,624)		—
Decreases related to prior year tax provisions		4,400		—		—
Increases related to current year tax provisions				(1,776)		—
Unrecognized tax benefits as of end of year	$	—	$	(4,400)	$	—

Related Party Transactions (Tables)

12 Months Ended

Dec. 31, 2016

Related Party Transactions


	Year Ended
	December 31,
	2016		2015		2014
Services provided by NST Consulting, LLC	$	323	$	455	$	467
Services provided to NST Consulting, LLC		(56)		(294)		(158)
General and administrative expense, net	$	267	$	161	$	309

Services provided by NST Consulting, LLC	$	246	$	52	$	—
Services provided to NST Consulting, LLC		(97)		(259)		(255)
Research and development expense, net	$	149	$	(207)	$	(255)

Services provided by NST Consulting, LLC	$	569	$	507	$	467
Services provided to NST Consulting, LLC		(153)		(553)		(413)
Total, net	$	416	$	(46)	$	54


Net payments made to (received from) NST	$	325	$	(46)	$	54

Quarterly Financial Information (unaudited) (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information [Table Text Block]


	March 31,		June 30,		September 30,		December 31,
2016 Quarter Ended
Revenue	$	—	$	—	$	—	$	—
Operating expenses		13,139		12,989		10,812		11,627
Other income, net		100		118		118		152
Net loss		(13,039)		(12,871)		(10,694)		(11,475)
Net loss attributable to common stockholders	$	(13,039)	$	(12,871)	$	(10,694)	$	(11,475)
Net loss per share attributable to common stockholders, basic and diluted	$	(0.65)	$	(0.62)	$	(0.50)	$	(0.49)

2015 Quarter Ended
Revenue	$	—	$	—	$	—	$	—
Operating expenses		2,629		2,596		10,640		4,802
Other income, net		6		2		7		89
Net loss		(2,623)		(2,594)		(10,632)		(4,714)
Net loss attributable to common stockholders	$	(3,280)	$	(3,270)	$	(11,652)	$	(4,927)
Net loss per share attributable to common stockholders, basic and diluted	$	(1.61)	$	(1.52)	$	(5.12)	$	(0.28)

Organization and Nature of Business - IPO, Stock Split, Liquidity (Details) $ / shares in Units, $ in Thousands					12 Months Ended
	Nov. 17, 2016 USD ($) $ / shares shares	Jun. 02, 2016 USD ($) $ / shares shares	Oct. 13, 2015 USD ($) $ / shares shares	Sep. 24, 2015	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Initial public offering
Number of shares issued \| shares	4,000,000
Issuance price (in dollars per share) \| $ / shares	$ 22.75
Gross proceeds	$ 91,000
Issuance of stock upon conversion, shares \| shares			11,677,076
Offering costs	188
Offering proceeds, net of discounts, commissions and expenses	$ 98,158
Proceeds from initial public offering, net of offering costs						$ 56,550
Proceeds from issuance of common stock in connection with private placement, net of issuance costs					$ 18,547
Reverse stock split				0.2899
Cash, cash equivalents and marketable securities					174,134
Proceeds from sale of stock, net of issuance costs					$ 98,158
IPO
Initial public offering
Number of shares issued \| shares			5,000,000
Issuance price (in dollars per share) \| $ / shares			$ 11.00
Gross proceeds			$ 55,000
Offering costs			2,272
Proceeds from initial public offering, net of offering costs			$ 56,550
Exercise of over-allotment option
Initial public offering
Number of shares issued \| shares	600,000		750,000
Issuance price (in dollars per share) \| $ / shares	$ 22.75		$ 11.00
Gross proceeds	$ 13,650		$ 8,250
Offering costs	$ 6,279		$ 4,428
Private Placement [Member]
Initial public offering
Number of shares issued \| shares		1,081,082
Issuance price (in dollars per share) \| $ / shares		$ 18.50
Gross proceeds		$ 20,000
Offering costs		153
Placement fees		1,300
Proceeds from issuance of common stock in connection with private placement, net of issuance costs		$ 18,547

Summary of Significant Accounting Policies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014
Assets Held for Sale
Assets held for sale, maximum holding period	1 year
Write-down of property and equipment held for sale	$ 216	$ 289
Assets held for sale	0	216
Deferred Offering Costs
Deferred offering costs	$ 116	0
Segment Reporting [Abstract]
Number of operating segments \| item	1
Research and Development Caption [Member]
Assets Held for Sale
Write-down of property and equipment held for sale	$ 216	$ 289
Computer equipment
Property and Equipment, Net
Depreciation period (in years)	3 years
Manufacturing equipment
Property and Equipment, Net
Depreciation period (in years)	5 years
Furniture and Fixtures [Member]
Property and Equipment, Net
Depreciation period (in years)	5 years
Employee, director and consultant stock options
Stock-Based Compensation
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%

Fair Value of Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Assets:
Marketable securities	$ 143,963	$ 82,187
Transfers from Level 1 to Level 2	0	0
Transfers from Level 2 to Level 1	0	0
Transfers into or out of Level 3	0	0
Recurring
Assets:
Cash equivalents	24,213	9,060
Marketable securities	143,963	82,187
Total assets measured at fair value	168,176	91,247
Recurring \| Level 1
Assets:
Cash equivalents	11,522	8,810
Total assets measured at fair value	11,522	8,810
Recurring \| Level 2
Assets:
Cash equivalents	12,691	250
Marketable securities	143,963	82,187
Total assets measured at fair value	$ 156,654	$ 82,437

Fair Value of Financial Assets and Liabilities - by type (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Marketable securities:
Amortized Cost	$ 144,012	$ 82,341
Gross Unrealized Gain	14
Gross Unrealized Loss	(63)	(154)
Fair Value	143,963	82,187
Corporate debt securities
Marketable securities:
Amortized Cost	51,352	46,270
Gross Unrealized Loss	(59)	(125)
Fair Value	51,293	46,145
Commercial paper
Marketable securities:
Amortized Cost	20,463	9,789
Fair Value	20,463	9,789
Asset-backed Securities [Member]
Marketable securities:
Amortized Cost	28,692	6,234
Gross Unrealized Gain	6
Gross Unrealized Loss	(1)	(14)
Fair Value	28,697	6,220
U.S. government agency debt securities
Marketable securities:
Amortized Cost	43,505	20,048
Gross Unrealized Gain	8
Gross Unrealized Loss	(3)	(15)
Fair Value	$ 43,510	$ 20,033

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Available-for-Sale Securities
-URI http://asc.fasb.org/extlink&oid=6505594

+ Details

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property and Equipment, net
Property and equipment	$ 607	$ 402
Accumulated depreciation	(126)	(42)
Property and equipment, net	481	360
Depreciation expense	120	90	$ 12
Write-down of property and equipment held for sale	216	289
Computer equipment
Property and Equipment, net
Property and equipment	310	262
Manufacturing equipment
Property and Equipment, net
Property and equipment	149	101
Furniture and Fixtures [Member]
Property and Equipment, net
Property and equipment	115	$ 39
Leasehold Improvements [Member]
Property and Equipment, net
Property and equipment	$ 33

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accrued Expenses
Research and development expenses	$ 1,166	$ 123
Employee compensation expenses	1,732
Licensing fees		250
Vixen contract payable.	100
Professional fees	77	283
Other	303	89
Total accrued expenses	$ 3,378	$ 745

Stockholders' Equity (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Oct. 13, 2015 shares	Dec. 31, 2016 USD ($) Vote $ / shares shares	Dec. 31, 2015 $ / shares shares	Aug. 28, 2015 shares
Stockholders' Equity
Preferred stock, shares authorized		10,000,000	10,000,000
Preferred stock, shares outstanding		0	0
Convertible preferred stock, shares outstanding				11,677,076
Issuance of stock upon conversion, shares	11,677,076
Common stock shares authorized		100,000,000	100,000,000
Common stock par value (in dollars per share) \| $ / shares		$ 0.00001	$ 0.00001
Number of votes per share \| Vote		1
Dividends declared \| $		$ 0

Stockholders' Equity - Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2012	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-based awards
Number of shares of stock issued to founders, including restricted stock	2,730,427
Number of shares of restricted stock issued	1,918,834
Granted, estimated grant-date fair value (in dollars per share)	$ 0.00001
Aggregate fair value of restricted stock awards vested during the year		$ 0	$ 6,423	$ 448
Restricted common stock \| Tranche One
Stock-based awards
Percentage of stock subject to vesting (as a percent)	25.00%
Vesting period (in years)	1 year
Restricted common stock \| Tranche Two
Stock-based awards
Percentage of stock subject to vesting (as a percent)	75.00%
Vesting period (in years)	3 years

Stock-Based Awards (Details) - shares		12 Months Ended			44 Months Ended
Stock-Based Awards (Details) - shares	Jan. 01, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 14, 2015	Oct. 31, 2015	Sep. 15, 2015
Stock-based awards
Options granted (in shares)		1,083,919	1,238,262	500,262
Options outstanding		2,702,350	1,738,524	500,262
Employee, director and consultant stock options
Stock Option Valuation
Risk-free interest rate (as a percent)		2.06%	1.78%	1.87%
Expected term (in years)		6 years 6 months	6 years 3 months 18 days	6 years 4 months 24 days
Expected volatility (as a percent)		94.86%	93.90%	113.90%
Expected dividend yield (as a percent)		0.00%	0.00%	0.00%
2012 Equity Compensation Plan
Stock-based awards
Number of shares available for grant						0
Term of award (in years)		10 years
Options granted (in shares)					1,140,524
Options outstanding		1,049,667	1,140,524
Vesting period (in years)		4 years
2015 Equity Incentive Plan
Stock-based awards
Number of shares authorized							1,643,872
Percentage increase to shares available for grant from common outstanding as of preceding December 31 (as a percent)		4.00%
Additional shares available	1,042,367
Number of shares available for grant		607,556
2015 Equity Incentive Plan \| Employee, director and consultant stock options
Stock-based awards
Exercise price as percentage of fair market value of common stock at grant date required, minimum		100.00%
2015 Equity Incentive Plan \| Employee, director and consultant stock options \| Maximum
Stock-based awards
Term of award (in years)		10 years

Stock-Based Awards - Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Options, Number of Shares
Number of Shares, beginning balance	1,738,524	500,262
Number of Shares, Granted	1,083,919	1,238,262	500,262
Number of Shares, Exercised	(51,980)
Number of Shares, Forfeited and canceled	(68,113)
Number of Shares, ending balance	2,702,350	1,738,524	500,262
Number of Shares, Options vested and expected to vest	2,702,350
Number of Shares, Options exercisable	575,149
Options, Weighted Average Exercise Price
Weighted Average Exercise Price, beginning balance (in dollars per share)	$ 13.23	$ 1.22
Weighted Average Exercise Price, Granted (in dollars per share)	27.12	18.08	$ 1.22
Weighted Average Exercise Price, Exercised (in dollars per share)	2.37
Weighted Average Exercise Price, Forfeited and canceled (in dollars per share)	15.71
Weighted Average Exercise Price, ending balance (in dollars per share)	18.94	$ 13.23	$ 1.22
Weighted Average Exercise Price, Options vested and expected to vest (in dollars per share)	18.94
Weighted Average Exercise Price, Options exercisable (in dollars per share)	$ 10.93
Options, Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term (in years)	9 years 18 days	9 years 6 months 4 days	9 years 9 months 7 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest (in years)	9 years 18 days
Weighted Average Remaining Contractual Term, Options exercisable (in years)	8 years 5 months 1 day
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 24,434	$ 24,722	$ 305
Aggregate Intrinsic Value, Options vested and expected to vest	24,434
Aggregate Intrinsic Value, Options exercisable	$ 9,512
Weighted average grant-date fair value of stock options granted (in dollars per share)	$ 21.16	$ 13.84	$ 1.38

Stock-Based Awards - RSUs (Details) - $ / shares	1 Months Ended	12 Months Ended
Stock-Based Awards - RSUs (Details) - $ / shares	Jul. 31, 2012	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
RSU, Weighted Average Grant Date Fair Value Per Unit
Granted, estimated grant-date fair value (in dollars per share)	$ 0.00001
Restricted Stock Units (RSUs) [Member]
RSU, Number of Units
Units outstanding, beginning of period		53,800
Granted		180,764	53,800	0
Number of shares, Vested		(12,950)
Forfeited and cancelled		(2,000)
Units outstanding, end of period		219,614	53,800
RSU, Weighted Average Grant Date Fair Value Per Unit
Weighted average grant date fair value, beginning balance (in dollars per share)		$ 28.68
Granted, estimated grant-date fair value (in dollars per share)		27.16	$ 28.68
Weighted average grant date fair value, vested (in dollars per share)		28.68
Forfeited and cancelled, estimated grant date fair value (in dollars per share)		28.68
Weighted average grant date fair value, ending balance (in dollars per share)		$ 27.43	$ 28.68

Stock-Based Awards - Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-based compensation expense
Stock-based compensation expense	$ 6,104	$ 891	$ 27
Unrecognized stock-based compensation cost, options	34,349
Unrecognized compensation, RSUs	5,790
Research and development expense.
Stock-based compensation expense
Stock-based compensation expense	2,291	257	10
General and administrative expense.
Stock-based compensation expense
Stock-based compensation expense	$ 3,813	$ 634	$ 17
Employee, director and consultant stock options
Stock-based compensation expense
Weighted average recognition period unrecognized stock-based compensation cost (in years)	3 years 5 months 27 days
Restricted Stock Units (RSUs) [Member]
Stock-based compensation expense
Weighted average recognition period unrecognized stock-based compensation cost (in years)	2 years 9 months 29 days

Net Loss per Share (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
Numerator:
Net loss	$ (11,475)	$ (10,694)	$ (12,871)	$ (13,039)	$ (4,714)	$ (10,632)	$ (2,594)	$ (2,623)	$ (48,079)	$ (20,563)	$ (8,517)
Accretion of convertible preferred stock										(2,566)	(2,054)
Net loss attributable to common stockholders	$ (11,475)	$ (10,694)	$ (12,871)	$ (13,039)	$ (4,927)	$ (11,652)	$ (3,270)	$ (3,280)	$ (48,079)	$ (23,129)	$ (10,571)
Denominator:
Weighted average shares of common stock outstanding (in shares)									21,415,733	6,637,678	2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding (in shares)										(530,636)	(1,010,345)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted (in shares)									21,415,733	6,107,042	1,720,082
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.49)	$ (0.50)	$ (0.62)	$ (0.65)	$ (0.28)	$ (5.12)	$ (1.52)	$ (1.61)	$ (2.25)	$ (3.79)	$ (6.15)

Net Loss per Share - Anti-dilution (Details) - shares	12 Months Ended
Net Loss per Share - Anti-dilution (Details) - shares	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	2,921,964	1,792,324	9,184,719
Employee, director and consultant stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	2,702,350	1,738,524	500,262
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	219,614	53,800
Restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders			759,538
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders			7,924,919

Commitments and Contingencies (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supply Agreement
Agreement term (in years)	3 years
Automatic renewal period (in years)		1 year
Termination fee, prior to FDA approval		$ 375
Termination fee, after FDA approval		275
Vixen [Member] \| Stock Purchase Agreement [Member]
Supply Agreement
Amount of required annual payment under the contract		100
JAKPharm and Key Organics [Member] \| License and collaboration agreement
Agreements for Office Space
Expenses incurred under related party transactions		50
Board of Directors Chairman [Member] \| Direct sublease agreement
Agreements for Office Space
Expenses incurred under related party transactions		254	$ 119	$ 66
Future minimum lease payments under the sublease
2017		350
2018		363
2019		339
Total		$ 1,052

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loss before income taxes
U.S. operations	$ (40,597)	$ (11,823)	$ (8,517)
Foreign operations	(7,482)	(8,740)
Loss before income taxes, Noncontrolling Interest, Total	$ (48,079)	$ (20,563)	$ (8,517)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate	(34.00%)	(34.00%)	(34.00%)
State taxes, net of federal benefit	(5.20%)	(3.80%)	(6.60%)
Foreign rate differential	3.20%	6.00%
Permanent differences	1.80%
Research and development tax credits	(2.00%)	(1.50%)	(1.00%)
Change in deferred tax asset valuation allowance	36.20%	33.30%	41.60%

Income Taxes - Deferred Assets and Liabilities, CFDs (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of net deferred tax assets
Net operating loss carryforwards	$ 16,836	$ 5,750
Capitalized start-up costs	8,840	4,401
Research and development tax credit carryforwards	1,480	500
Capitalized research and development expenses	594	611
Intangible assets	1,403	1,650
Stock‑based compensation expenses	2,629	373
Property and equipment	199
Other	2	1
Total deferred tax assets	31,983	13,286
Section 481 (a) adjustment	(1,257)
Total deferred tax liabilities	(1,257)
Valuation allowance	(30,726)	(13,286)	$ (6,444)	$ (2,899)
United Kingdom Tax Authority
Components of net deferred tax assets
Operating Loss Carryforwards	7,972
Federal
Components of net deferred tax assets
Research and development tax credit carryforwards		$ 1,488
Operating Loss Carryforwards	38,137
Federal \| Research Tax Credit Carryforward [Member]
Components of net deferred tax assets
Tax Credit Carryforward, Amount	1,488
State
Components of net deferred tax assets
Operating Loss Carryforwards	38,137
State \| Research Tax Credit Carryforward [Member]
Components of net deferred tax assets
Tax Credit Carryforward, Amount	$ 1,488

Income Taxes - Valuation Allowance and Unrecognized Benefits (Details) - USD ($) $ in Thousands	12 Months Ended			36 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Changes in valuation allowance for deferred tax assets
Valuation allowance at beginning of year	$ (13,286)	$ (6,444)	$ (2,899)	$ (2,899)
Increases recorded to income tax provision	(17,440)	(6,842)	(3,545)
Valuation allowance as of end of year	(30,726)	(13,286)	$ (6,444)	(30,726)
Unrecognized Tax Benefits
Unrecognized Tax Benefits, Beginning Balance	(4,400)
Increases related to prior year tax provisions		(2,624)
Decreases related to prior year tax provisions	4,400
Increases related to current year tax provisions		(1,776)
Unrecognized Tax Benefits, Ending Balance		(4,400)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 0	$ 0		0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense				$ 0

Related Party Transactions (Details) - Board of Directors Chairman [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Direct sublease agreement
Related Party Transactions
Expenses incurred under related party transactions	$ 254	$ 119	$ 66
Direct sublease agreement \| NST, LLC [Member]
Related Party Transactions
Expenses incurred under related party transactions	387	124	66
Services agreement \| NST, LLC [Member]
Related Party Transactions
Expenses incurred under related party transactions	569	507	467
Other revenue earned from related party transactions	(153)	(553)	(413)
Net expenses (revenues) from related party transactions	416	(46)	54
Amount due to related party	91	0
Payments to related party	325		54
Receipts from related party		(46)
Services agreement \| NST, LLC [Member] \| General and administrative expense.
Related Party Transactions
Expenses incurred under related party transactions	323	455	467
Other revenue earned from related party transactions	(56)	(294)	(158)
Net expenses (revenues) from related party transactions	267	161	309
Services agreement \| NST, LLC [Member] \| Research and development expense.
Related Party Transactions
Expenses incurred under related party transactions	246	52
Other revenue earned from related party transactions	(97)	(259)	(255)
Net expenses (revenues) from related party transactions	$ 149	$ (207)	$ (255)

Agreements Related to Intellectual Property (Details) $ in Thousands		1 Months Ended	12 Months Ended
	Mar. 24, 2016 USD ($) shares	Aug. 31, 2012	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
License Agreement
Upfront payment recorded as research and development expense			$ 33,476	$ 15,339	$ 6,507
Assignment Agreement and Finder's Services Agreement [Member] \| A-101
License Agreement
Number Of Products \| item			1
Milestone payment						$ 400
Maximum aggregate payments owed upon achievement of specified pre-commercialization milestones			$ 1,000
Maximum additional payments owed upon achievement of second set of development milestones			4,500
Term of Agreement, Minimum		15 years
Assignment Agreement and Finder's Services Agreement [Member] \| A-101 \| General and administrative expense.
License Agreement
Milestone payment			$ 300
Stock Purchase Agreement [Member]
License Agreement
Number Of Products \| item			3
Maximum aggregate payments owed upon achievement of specified pre-commercialization milestones			$ 18,000
Maximum additional payments owed upon achievement of second set of development milestones			$ 22,500
Term of Agreement, Minimum			10 years
Upfront payment recorded as research and development expense	$ 600
Entity stock issued in stock purchase \| shares	159,420
Stock Issued During Period, Value, Purchase of Assets			$ 2,355
Number of annual payments \| item			6
Stock Purchase Agreement [Member] \| Vixen [Member]
License Agreement
Amount Of Fixed Annual Payment			$ 100
License and collaboration agreement \| Rigel \| JAK inhibitors
License Agreement
Maximum aggregate payments owed upon achievement of specified pre-commercialization milestones			80,000
Maximum additional payments owed upon achievement of second set of development milestones			$ 10,000
Upfront payment recorded as research and development expense				8,000
Period from first commercial product sale that royalties are owed (in years)			10 years
Commercial License Agreement
License Agreement
Maximum additional payments owed upon achievement of second set of development milestones			$ 11,600
Term of Agreement, Minimum			10 years
Annual maintenance fee			$ 10
Commercial License Agreement \| JAKPharm and Key Organics [Member] \| Products Containing Specified Compounds [Member]
License Agreement
Maximum aggregate payments owed upon achievement of specified pre-commercialization milestones			$ 2,350
Upfront payment recorded as research and development expense				$ 250
Period from first commercial product sale that royalties are owed (in years)			10 years
Written termination notice period			3 months
Annual maintenance fee			$ 50

401(k) Savings Plan (Details) - USD ($) $ in Thousands	12 Months Ended
401(k) Savings Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Employer match of employee contributions (as a percent)	100.00%
Employee earnings subject to employer match (as a percent)	4.00%
Company contributions	$ 176	$ 99	$ 60

Quarterly Financial Information (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	$ 11,627	$ 10,812	$ 12,989	$ 13,139	$ 4,802	$ 10,640	$ 2,596	$ 2,629	$ 48,567	$ 20,667	$ 8,533
Other income, net	152	118	118	100	89	7	2	6
Net loss	(11,475)	(10,694)	(12,871)	(13,039)	(4,714)	(10,632)	(2,594)	(2,623)	(48,079)	(20,563)	(8,517)
Net loss attributable to common stockholders	$ (11,475)	$ (10,694)	$ (12,871)	$ (13,039)	$ (4,927)	$ (11,652)	$ (3,270)	$ (3,280)	$ (48,079)	$ (23,129)	$ (10,571)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.49)	$ (0.50)	$ (0.62)	$ (0.65)	$ (0.28)	$ (5.12)	$ (1.52)	$ (1.61)	$ (2.25)	$ (3.79)	$ (6.15)

Organization and Nature of Business (Details)	Dec. 31, 2016 item
A-101
Production information
Number of clinical trials completed	3