Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2015	Mar. 23, 2016	Jun. 30, 2015
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, 2015
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	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		20,157,503
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Entity Public Float			$ 0

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 9,851	$ 10,757
Marketable securities	75,017	5,373
Prepaid expenses and other current assets	1,656	204
Total current assets	86,524	16,334
Marketable securities	7,170	518
Property and equipment, net	360	515
Other assets	22	10
Total assets	94,076	17,377
Current liabilities:
Accounts payable	810	1,263
Accrued expenses	745	188
Total current liabilities	1,555	1,451
Deferred rent		4
Total liabilities	$ 1,555	$ 1,455
Commitments and contingencies (Note 10)
Convertible preferred stock (Series A, B and C), $0.00001 par value; 34,090,000 shares authorized at December 31, 2014; 27,341,057 shares issued and outstanding at December 31, 2014; aggregate liquidation preference of $35,882 at December 31, 2014		$ 36,677
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 100,000,000 and 77,000,000 shares authorized and no shares issued at December 31, 2015; no shares authorized at December 31, 2014
Additional paid-in capital	$ 135,503
Accumulated other comprehensive loss	(149)	$ (6)
Accumulated deficit	(42,833)	(20,749)
Total stockholders’ equity (deficit)	92,521	(20,755)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 94,076	$ 17,377

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Consolidated Balance Sheets
Convertible preferred stock, par value (in dollars per share)		$ 0.00001
Convertible preferred stock, shares authorized		34,090,000
Convertible preferred stock, shares issued		27,341,057
Convertible preferred stock, shares outstanding		27,341,057
Liquidation Preference		$ 35,882
Preferred stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized	100,000,000	77,000,000
Common stock, shares issued	20,157,503	2,730,427
Common stock, shares outstanding	20,157,503	2,730,427

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating expenses:
Research and development	$ 15,339	$ 6,507	$ 3,488
General and administrative	5,328	2,026	1,769
Total operating expenses	20,667	8,533	5,257
Loss from operations	(20,667)	(8,533)	(5,257)
Interest income	104	16	21
Net loss	(20,563)	(8,517)	(5,236)
Accretion of convertible preferred stock	(2,566)	(2,054)	(1,740)
Net loss attributable to common stockholders	$ (23,129)	$ (10,571)	$ (6,976)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (3.79)	$ (6.15)	$ (6.45)
Weighted average common shares outstanding, basic and diluted (in shares)	6,107,042	1,720,082	1,081,347
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities, net of tax of $0	$ (148)	$ (9)	$ 3
Foreign currency translation adjustments	5
Total other comprehensive income (loss)	(143)	(9)	3
Comprehensive loss	$ (20,706)	$ (8,526)	$ (5,233)

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balance at Dec. 31, 2012					$ 21,260
Balance (in shares) at Dec. 31, 2012					20,890,000
Increase (Decrease) in Temporary Equity
Accretion of convertible preferred stock to redemption value					$ 1,740
Balance at Dec. 31, 2013					$ 23,000
Balance (in shares) at Dec. 31, 2013					20,890,000
Balance at Dec. 31, 2012				$ (2,190)	$ (2,190)
Balance (in shares) at Dec. 31, 2012	2,730,427
Increase (Decrease) in Stockholders' Equity
Unrealized gain (loss) on marketable securities			$ 3		3
Accretion of convertible preferred stock, equity effect				(1,740)	(1,740)
Net loss				(5,236)	(5,236)
Balance at Dec. 31, 2013			3	(9,166)	(9,163)
Balance (in shares) at Dec. 31, 2013	2,730,427
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
Increase (Decrease) in Stockholders' Equity
Unrealized gain (loss) on marketable securities			(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				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
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)
Accretion of convertible preferred stock to redemption value					$ 1,764
Increase (Decrease) in Stockholders' Equity
Stock Issued During Period, Value, New Issues		56,550			56,550
Stock Issued During Period, Shares, New Issues	5,750,000
Stock Issued During Period, Value, Conversion of Convertible Securities		78,305			78,305
Stock Issued During Period, Shares, Conversion of Convertible Securities	11,677,076
Unrealized gain (loss) on marketable securities			(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

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014
Issuance costs		$ 2,272
Temporary equity, issuance costs		$ 136	$ 60
Series B convertible preferred stock
Temporary equity, issuance costs	$ 60

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (20,563)	$ (8,517)	$ (5,236)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	90	12	11
Stock-based compensation expense	891	27
Deferred rent, amortization of deferred credits	(5)
Deferred rent, amortization of deferred charges		1	3
Write-down of property and equipment held for sale	289
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,269)	(152)	7
Accounts payable	(359)	819	303
Accrued expenses	557	174	(8)
Net cash used in operating activities	(20,369)	(7,636)	(4,920)
Cash flows from investing activities:
Purchases of property and equipment	(507)	(417)
Purchases of marketable securities	(82,513)	(5,035)	(4,535)
Proceeds from sales and maturities of marketable securities	6,069	3,673
Net cash used in investing activities	(76,951)	(1,779)	(4,535)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	39,864	10,584
Proceeds from initial public offering, net of offering costs	56,550
Net cash provided by financing activities	96,414	10,584
Net (decrease) increase in cash and cash equivalents	(906)	1,169	(9,455)
Cash and cash equivalents at beginning of period	10,757	9,588	19,043
Cash and cash equivalents at end of period	9,851	10,757	9,588
Supplemental disclosures of non-cash investing and financing activities:
Additions to property and equipment purchases included in accounts payable	2	91
Accretion of convertible preferred stock to redemption value	$ 1,764	2,054	$ 1,740
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, 2015
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. (together with ATIL referred to as the “Company”). The Company is a clinical‑stage specialty pharmaceutical 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, is a proprietary high‑concentration 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 2 clinical trials of A-101 in patients with SK. 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. 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 (see Note 6). 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. 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, 2015, the Company had cash, cash equivalents and marketable securities of $92,038 and an accumulated deficit of $42,833. 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 products will require significant additional financing. The Company expects that its cash, cash equivalents and marketable securities as of December 31, 2015 will be sufficient to fund its operations for a period greater than 12 months 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, 2015

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 subsidiary, ATIL. 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 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 or income. Gains and losses resulting from foreign currency transactions are reflected within the Company’s results of operations. The Company has not utilized any 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 and recognizes compensation expense for share-based awards expected to vest on a straight-line basis over their requisite service period, which is generally the vesting period of the respective award. The Company has issued stock options and restricted stock unit awards with service-based vesting conditions.

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 is remeasured using the then current fair value of the stock-based award, based on updated assumption inputs in the Black-Scholes option pricing model.

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 Company recognizes compensation expense for only the portion of awards that are expected to vest. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre vesting forfeitures for service based awards. The impact of a forfeiture rate adjustment will be recognized in full in the period of adjustment, and if the actual forfeiture rate is materially different from the Company’s estimate, the Company may be required to record adjustments to stock-based compensation expense in future periods.

The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. Prior to the IPO, the Company was a private company and lacked company specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing 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. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. Prior to the IPO, the Company valued its common stock using a hybrid method which used market approaches to estimate enterprise value. The hybrid method used was a probability-weighted expected return method which is 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 restricted stock unit award is measured as the aggregate difference between the purchase price per share of the award, if any, and the fair value per share 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 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 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.

Accretion of Convertible Preferred Stock

Accretion of convertible preferred stock includes 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 per share calculation (see Note 6). 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 and, if dilutive, the weighted average number of potential shares of common stock, including the assumed exercise of stock options and unvested restricted stock. Prior to the IPO, the Company applied the two-class method to calculate its basic and diluted net loss per share attributable to common stockholders, as its convertible preferred stock and common stock are participating securities. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to common stockholders. However, the two-class method does not impact the net loss per share of common stock as the Company was in a net loss position for each of the periods presented and preferred stockholders do not participate in losses.

The Company’s convertible preferred stock contractually entitles the holders of such shares to participate in dividends but does not contractually require the holders of such shares to participate in losses of the Company. Similarly, restricted stock awards granted by the Company entitle the holder of such awards to dividends declared or paid by the board of directors, regardless of whether such awards are unvested, as if such shares were outstanding common shares at the time of the dividend. However, the unvested restricted stock awards are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

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 consist of money market accounts 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 are included in other income (expense) within the 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, and believes it is probable that the sale of the assets will occur sometime in 2016. The Company utilized the third-party seller’s estimate of the fair value of the machinery. During the year ended December 31, 2015, the Company recorded an impairment charge of $289 to write the assets down to their net realizable value. The impairment charge is included in research and development expense on the Company’s consolidated statement of operations and comprehensive loss. As of December 31, 2015, $216 in assets were classified as held for sale.

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 capitalizes certain legal, accounting and other third party fees that are directly associated with in-process equity financings as deferred offering costs (non-current) until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. The Company did not record any deferred offering costs as of December 31, 2015 or 2014.

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 seven years. 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 November 2015, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“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.

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 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.

Fair Value of Financial Assets and Liabilities

12 Months Ended

Dec. 31, 2015

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 Company’s assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values:


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


	Fair Value Measurements as of December 31,
	2014 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	10,012	$	—	$	—	$	10,012
Marketable securities		—		5,891		—		5,891
	$	10,012	$	5,891	$	—	$	15,903

As of December 31, 2015, the Company’s cash equivalents consisted of money market funds and corporate debt securities with original maturities of less than three months. As of December 31, 2014, the Company’s cash equivalents consisted of money market funds. The Company valued its money market funds based on Level 1 inputs. In determining the fair value of its corporate debt securities, commercial paper, asset-backed securities and U.S. government agency debt securities as of December 31, 2015 and 2014, the Company relied on quoted prices for identical securities in markets that are not active, a Level 2 input. 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. During the years ended December 31, 2015 and 2014, there were no transfers between Level 1, Level 2 and Level 3.

As of December 31, 2015 and 2014, the fair value of the Company’s available-for-sale marketable securities by type of security was as follows:


	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


	December 31, 2014
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gain		Loss		Value
Marketable securities:
Corporate debt securities	$	5,096	$	—	$	(6)	$	5,090
U.S. government agency debt securities		801		—		—		801
Total marketable securities	$	5,897	$	—	$	(6)	$	5,891

As of December 31, 2015 and 2014, the Company’s investments in corporate debt securities had credit ratings of A and above and remaining maturities of less than 15 months and less than 13 months, respectively.

- 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, 2015

Property and Equipment, Net

Property and Equipment, Net

4. Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
	2015		2014
Computer equipment	$	262	$	36
Manufacturing equipment		101		—
Construction in progress		—		506
Furniture and fixtures		39		—
		402		542
Less: Accumulated depreciation		(42)		(27)
	$	360	$	515

Depreciation expense was $90, $12 and $11 for the years ended December 31, 2015, 2014 and 2013, respectively. The company also recorded a $289 write-down of manufacturing equipment held for sale to its net realizable value during the year ended December 31, 2015.

Accrued Expenses

12 Months Ended

Dec. 31, 2015

Accrued Expenses

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following:


	December 31,
	2015		2014
Clinical trial expenses	$	123	$	163
Licensing fees		250		—
Professional fees		283		—
Other		89		25
	$	745	$	188

Convertible Preferred Stock

12 Months Ended

Dec. 31, 2015

Convertible Preferred Stock.

Convertible Preferred Stock

6. Convertible Preferred Stock

The Company issued Series A, Series B and Series C convertible preferred stock (collectively, the “Preferred Stock”). As of December 31, 2014, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 34,090,000 shares of Preferred Stock, $0.00001 par value.

In September 2014, the Company entered into a stock purchase agreement pursuant to which the Company agreed to sell to the investors an initial issuance (the “First Tranche”) of 6,451,057 shares of Series B convertible preferred stock (the “Series B preferred stock”) at $1.65 per share for gross proceeds of $10,644. Per the terms of that stock purchase agreement, upon the successful attainment of two specified milestones, the Company was entitled to call a second tranche of 6,451,057 shares of Series B preferred stock at $1.65 per share (the “purchased put option”). The Company had the right, but not the obligation, to exercise its purchased put option after successful attainment of the specified milestones as confirmed by a vote of five‑sixths of the members of the Company’s board of directors and 60% of voting stockholders of the Company. The two milestones related to (i) the successful achievement of the primary efficacy endpoint and demonstrated safety of a specified Phase 2b clinical trial of A-101 in patients with SK, and (ii) the occurrence of an end of Phase 2 meeting with the U.S. Food and Drug Administration (“FDA”), as a result of which the FDA did not raise any objection to the Company proceeding to a Phase 3 clinical trial of A-101 in patients with SK.

In connection with the initial issuance of Series B preferred stock in September 2014, the Company recorded the First Tranche transaction, net of issuance costs of $60, and the $1,039 issuance‑date fair value of the purchased put option. The purchased put option was recorded as a charge to accumulated deficit within stockholders’ deficit and as an increase to the carrying value of Series B preferred stock based on the Company’s conclusion that the purchased put option met the equity classification criteria at time of issuance as the purchased put option (i) was a freestanding financial instrument that did not require the Company to issue shares that are potentially redeemable and (ii) required gross physical settlement in all circumstances.

The fair value of the purchased put option was determined on the date of its issuance using the Black‑Scholes option‑pricing model with the following assumptions and inputs: risk‑free interest rate of 0.08%, expected term of nine months, expected volatility of 80.0%, no expected dividends and fair value of underlying instruments of $1.65. The fair value calculation also included an estimate of a 60% probability of occurrence of the successful attainment of the specified milestones that triggered the Company’s ability to exercise the purchased put option, as well as an estimate of a 60% probability of the Company exercising the purchased put option, if it became exercisable.

On August 28, 2015, the Company issued 12,944,984 shares of Series C convertible preferred stock (“Series C preferred stock”) at a price of $3.09 per share for gross proceeds of $40,000. In connection with the closing of the Series C preferred stock financing, the terms of a qualified public offering requiring the conversion of all shares of the Company’s Preferred Stock into common stock were changed and the Series B preferred stock purchase agreement was amended to terminate the Company’s purchased put option with respect to a second tranche of Series B preferred stock.

The Preferred Stock was subject to redemption under certain deemed liquidation events, and as such, the Preferred Stock was considered contingently redeemable for accounting purposes. Accordingly, the Preferred Stock was recorded within temporary equity in the consolidated financial statements. The Company has not adjusted the Preferred Stock to its redemption amount at each reporting period, as the redemption of such Preferred Stock was not deemed probable of occurrence during the periods presented. The redemption of the Preferred Stock was not considered probable as the redemption was contingent on the occurrence of such deemed liquidation events which the Company concluded were not probable for the periods presented.

Preferred Stock consisted of the following at December 31, 2014:


	December 31, 2014
		Preferred					Common
	Preferred	Shares					Stock Issuable
	Shares	Issued and	Carrying		Liquidation		Upon
	Authorized	Outstanding	Value		Preference		Conversion
Series A redeemable convertible preferred stock	20,890,000	20,890,000	$	24,879	$	25,023	6,055,060
Series B redeemable convertible preferred stock	13,200,000	6,451,057		11,798		10,859	1,869,859
	34,090,000	27,341,057	$	36,677	$	35,882	7,924,919

The holders of the Preferred Stock had the following rights and preferences prior to their conversion under the Company’s IPO:

Dividends

The holders of Preferred Stock were entitled to receive, on a pari passu basis, cumulative dividends, in cash, at the rate of 8% per year on the applicable Original Issue Price (as defined below) and accrued but unpaid dividends. Dividends accrued on a daily basis, whether or not earned or declared, irrespective of the availability of profits or surplus and compounded annually on the anniversary of the date of original issuance. Dividends on the Preferred Stock were payable upon redemption of the Preferred Stock or upon liquidation. The Original Issue Price for Series A, Series B, and Series C convertible preferred stock was $1.00, $1.65, and $3.09, respectively, per share, subject to appropriate adjustment in the event of any stock dividend, stock split, combination or recapitalization affecting the Preferred Stock. In addition, if dividends had been declared on shares of common stock, the Company was required to declare at the same time a dividend payable to the holders of Preferred Stock equivalent to the dividend amount they would have received if each preferred share were converted into common stock. The Company was not permitted to pay dividends to common stockholders until all dividends accrued or declared but unpaid on the Preferred Stock had been paid in full.

Liquidation Preference

In the event of any liquidation dissolution or winding up of the Company, either voluntary or involuntary, or in the event of Deemed Liquidation Event (as defined below), holders of Preferred Stock were entitled to receive, in preference to all other stockholders, and to the extent available, an amount equal to the Original Issue Price, adjusted for any stock dividends, stock splits or recapitalizations, plus any accruing dividend accrued but unpaid, whether or not earned or declared. In the event that proceeds were not sufficient to permit payment in full to these holders, the proceeds would have been ratably distributed among the holders of Preferred Stock on a pari passu basis to the full preferential amount each such holder was otherwise entitled to receive.

After payments had been made in full to the holders of Preferred Stock, then, to the extent available, holders of the common stock and Preferred Stock were entitled to participate in the distribution of the remaining assets, pro rata based on the number of shares of common stock held by each (on an as-converted to common basis).

Unless the holders of at least 60% of the then outstanding shares of the Preferred Stock, voting together as a single class on an as-converted basis, elected otherwise, a Deemed Liquidation Event would have included a merger or consolidation (other than one in which stockholders of the Company own a majority by voting power of the outstanding shares of the surviving or acquiring corporation) or a sale, lease, transfer, exclusive license or other disposition of all or substantially all of the assets of the Company.

Conversion

Each share of Preferred Stock was convertible into common stock at the option of the stockholder at any time after the date of issuance. Each share of the Preferred Stock would have been converted into shares of common stock, at the applicable conversion ratio of each series of Preferred Stock then in effect, upon the earlier of (i) a qualified public offering with net proceeds of not less than $40,000 and a price of not less than $12.80 per share, subject to appropriate adjustment for any stock dividend, stock split, combination or other similar recapitalization, and (ii) the date specified by written consent or agreement of the holders of 60% of the then-outstanding shares of Preferred Stock voting together as a single class (on an as-converted basis).

The conversion ratio of each series of Preferred Stock was determined by dividing the Original Issue Price of each series of preferred stock by the Conversion Price of each series. The Conversion Price of each series was $3.45 for Series A, $5.6925 for Series B, and $10.6605 for Series C and was subject to adjustment as set forth in the Company's certificate of incorporation, as amended and restated. As of December 31, 2014, all outstanding shares of Series A, Series B, and Series C preferred stock were convertible into common stock on a 3.45-for-one basis.

Redemption

At the written election of the holders of at least 60% of the outstanding Series A preferred stock, voting together as a single class, the shares of Series A preferred stock outstanding could have been redeemed at any time on or after September 30, 2019, in three annual installments commencing sixty days after receipt of the required vote, at the Original Issue Price per share of Series A preferred stock plus all accruing dividends accrued thereon, whether or not declared, together with any other dividends declared but unpaid thereon.

At the written election of the holders of at least 60% of the outstanding Series B preferred stock, voting together as a single class, the shares of Series B preferred stock outstanding could have been redeemed at any time on or after September 30, 2019, in three annual installments commencing sixty days after receipt of the required vote, at the Original Issue Price per share of Series B preferred stock plus all accruing dividends accrued thereon, whether or not declared, together with any other dividends declared but unpaid thereon.

The Company would have redeemed the shares on a pro rata basis in accordance with the number of shares of Series A or Series B preferred stock held by each stockholder. No shares of Series A preferred stock shall be redeemed so long as any shares of Series B preferred stock remain issued and outstanding.

There was no redemption feature associated with the Series C preferred stock.

In connection with the closing of the Series C preferred stock financing, the redemption rights of the Series A and Series B preferred stock were removed as of August 25, 2015. As a result of the removal of the redemption rights the Company ceased recording accretion of the carrying values of Series A and Series B preferred stock to their respective redemption values through September 30, 2019, which had been the first required redemption date. The accretion for the year ended December 31, 2015 represents both the issuance costs and cumulative accrued but unpaid dividends through August 28, 2015. Subsequent to August 28, 2015, the Company was no longer required to record the accumulated undeclared dividends on its balance sheet, but is required to deduct accumulated undeclared dividends as part of its loss per share calculation.

Voting Rights

The holders of Preferred Stock were entitled to vote, together with the holders of common stock, on all matters submitted to stockholders for a vote. Holders of Preferred Stock had the right to vote the number of shares equal to the number of shares of common stock into which such Preferred Stock could convert on the record date for determination of stockholders entitled to vote. The holders of the majority of Preferred Stock, voting separately as a class, were entitled to elect three directors of the Company.

As discussed in Note 1, the Company completed its IPO in October 2015. Upon the closing of the IPO, all of the Company’s 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. No shares of preferred stock were outstanding at December 31, 2015.

Stockholders' Equity (Deficit)

12 Months Ended

Dec. 31, 2015

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)

7. Stockholders’ Equity (Deficit)

Common Stock

As of December 31, 2015 and 2014, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 100,000,000 shares and 77,000,000 shares, respectively, 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, 2015.

Restricted Common Stock

The Company had granted restricted common stock with time‑based vesting conditions. Unvested shares of restricted common stock may not have been sold or transferred by the holder. These restrictions lapsed according to the time‑based vesting conditions of each award and upon the Company’s initial public offering, all unvested shares of restricted common stock vested immediately.

In July 2012, the Company issued 2,730,427 shares of common stock to its founders in connection with the Company’s formation, of which 1,918,834 shares were subject to vesting pursuant to restricted stock agreements, with 25% of such shares vesting in July 2013 and the remaining 75% vesting in equal monthly installments over a three-year period thereafter. The estimated grant‑date fair value of these restricted common shares was $0.00001 per share, equal to the par value of each share. As of December 31, 2015 and 2014, 0 shares and 759,538 shares, respectively, were subject to repurchase.

The table below summarizes the Company’s restricted stock activity since January 1, 2015:


		Weighted
		Average Grant
	Number	Date Fair Value
	of Shares	Per Share
Unvested restricted common stock as of December 31, 2013	1,239,247	$	0.00001
Vested	(479,709)	$	0.00001
Unvested restricted common stock as of December 31, 2014	759,538	$	0.00001
Vested	(759,538)	$	0.00001
Unvested restricted common stock as of December 31, 2015	—	$	0.00001

The aggregate fair value of restricted stock awards that vested during the years ended December 31, 2015, 2014 and 2013 was $6,423, $448 and $281, respectively.

- 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 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(d),(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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 310
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 4.E)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74512-122707

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 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29-31)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 6: 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 7: 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 8: 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 9: 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 10: 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 11: 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 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section E

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section C

+ Details

Stock-Based Awards

12 Months Ended

Dec. 31, 2015

Stock-Based Awards

Stock-Based Awards

8. Stock‑Based Awards

2012 Equity Compensation Plan

The Company’s 2012 Equity Compensation Plan, as amended and restated (the “2012 Plan”), provides for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company. The 2012 Plan is administered by the 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, or their committee if so delegated, 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 generally grants stock‑based awards with service conditions only (“service‑based” awards).

Stock options granted under the 2012 Plan generally vest over four years and expire after ten years.

The total number of shares of common stock that may be issued under the 2012 Plan was 500,262 shares as of December 31, 2014. On August 25, 2015, the Company effected an increase in the number of shares of common stock reserved for issuance under the 2012 Plan from 500,262 shares to 1,539,169 shares.

As required by the 2012 Plan, the exercise price for stock options granted was not to be less than the fair value of common shares as determined by the Company as of the date of grant. The Company valued its common stock by taking into consideration its most recently available valuation of common shares performed by management and the board of directors as well as additional factors which may have changed since the date of the most recent contemporaneous valuation through the date of grant.

As of December 31, 2015, no shares remained available for grant under the 2012 Plan.

2015 Equity Incentive Plan

On September 15, 2015, the Company’s board of directors adopted and on September 16, 2015, the Company’s stockholders approved the 2015 Equity Incentive Plan (the “2015 Plan”), which became effective in connection with the IPO in October 2015. As of the time the 2015 Plan became effective, no further grants may be made under the 2012 Plan. The 2015 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit 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 2,784,395. 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.

Stock Option Valuation

The assumptions that the Company used to determine the fair value of the stock options granted to employees, non-employees and directors were as follows, presented on a weighted average basis:


	Year Ended		Year Ended
	December 31, 2015		December 31, 2014

Risk-free interest rate	1.78	%	1.87	%
Expected term (in years)	6.3		6.4
Expected volatility	93.9	%	113.9	%
Expected dividend yield	0	%	0	%

The Company recognizes compensation expense for only the portion of awards that are expected to vest. For the year ended December 31, 2015 and December 31, 2014 the Company applied an expected forfeiture rate of 0%. No awards were granted during the year ended December 31, 2013.

Stock Options

The following table summarizes stock option activity under the 2012 Plan and 2015 Plan from January 1, 2013 through December 31, 2015:


					Weighted
			Weighted		Average
			Average		Remaining	Aggregate
	Number		Exercise		Contractual	Intrinsic
	of Shares		Price		Term	Value
					(in years)
Outstanding as of January 1, 2013	—			—	—		—
Granted	—			—
Exercised	—			—
Forfeited and canceled	—			—
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
Options vested and expected to vest as of December 31, 2015	1,738,524		$	13.23	9.51	$	24,722
Options exercisable as of December 31, 2015	147,672	(1)	$	1.19	8.72	$	3,803

(1)

All options granted to date 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, 2015.

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

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock.

Restricted Stock Units

The Company did not grant any RSUs during the years ended December 31, 2014 and 2013. A summary of the status of the Company's RSUs at December 31, 2015 and of changes in RSUs outstanding under the 2015 Plan for the year ended December 31, 2015 is as follows:


		Weighted
		Average
		Grant Date
	Number	Fair Value
	of Shares	Per Share
Outstanding at December 31, 2014	—	$	—
Granted	53,800		28.68
Vested	—		—
Forfeited and cancelled	—		—
Outstanding at December 31, 2015	53,800	$	28.68

For awards that vest subject to the satisfaction of service requirements, compensation expense is measured based on the fair value of the RSUs on the date of grant and is recognized as expense on a straight-line basis, net of estimated forfeitures, over the requisite service period. All RSUs issued vest over time as stipulated in the individual RSU agreements. In the event of a change in control, the unvested RSUs will be accelerated and fully vested immediately prior to the change in control. There are no performance based features or market conditions.

Stock‑Based Compensation

For the years ended December 31, 2015, 2014 and 2013, the Company recorded stock-based compensation in the following expense categories of its statements of operations and comprehensive loss:


	Year Ended
	December 31,
	2015		2014		2013
Research and development	$	257	$	10	$	—
General and administrative		634		17		—
	$	891	$	27	$	—

As of December 31, 2015, the Company had an aggregate of $19,093 of unrecognized stock‑based compensation cost, which is expected to be recognized over weighted average periods of 3.51 years.

Net Loss per Share

12 Months Ended

Dec. 31, 2015

Net Loss per Share

Net Loss per Share

9. Net Loss per Share

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


	Year Ended
	December 31,
	2015		2014		2013
Numerator:
Net loss	$	(20,563)	$	(8,517)	$	(5,236)
Accretion of redeemable convertible preferred stock to redemption value		(2,566)		(2,054)		(1,740)
Net loss attributable to common stockholders	$	(23,129)	$	(10,571)	$	(6,976)
Denominator:
Weighted average shares of common stock outstanding		6,637,678		2,730,427		2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding		(530,636)		(1,010,345)		(1,649,080)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted		6,107,042		1,720,082		1,081,347
Net loss per share attributable to common stockholders, basic and diluted	$	(3.79)	$	(6.15)	$	(6.45)

To calculate net loss attributable to common stockholders for the period, 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 include stock options, RSUs, unvested restricted common stock and convertible preferred stock, have been excluded from the computation of diluted net loss per share as 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 potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated:


	Year Ended December 31,
	2015	2014	2013

Stock options to purchase common stock	1,738,524	500,262	—
Restricted stock unit awards	53,800	—	—
Unvested restricted common stock	—	759,538	1,239,247
Convertible preferred stock (as converted to common stock)	—	7,924,919	6,055,060
	1,792,324	9,184,719	7,294,307

Commitments and Contingencies

12 Months Ended

Dec. 31, 2015

Commitments and Contingencies

Commitments and Contingencies

10. Commitments and Contingencies

Sublease

In September 2013, the Company entered into a sublease agreement for its office space with related parties (see Note 12), 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. Rent expense under operating subleases was $119 and $66 for the years ended December 31, 2015 and 2014, respectively. The Company recognizes rent expense on a straight line basis over the sublease period and has accrued for rent expense incurred but not yet paid.

As of December 31, 2015, future minimum lease payments under the sublease were as follows:


Years Ending December 31,
2016	$	237
2017		263
2018		268
2019		251
2020		—
Total	$	1,019

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, 2014 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 intends to use to dispense A-101 in Phase 3 clinical trials and 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, 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, 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.

Income Taxes

12 Months Ended

Dec. 31, 2015

Income Taxes

Income Taxes

11. Income Taxes

During the years ended December 31, 2015, 2014 and 2013, 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,
	2015		2014		2013
U.S. operations	$	(11,823)	$	(8,517)	$	(5,236)
Foreign operations		(8,740)		—		—
Loss before income taxes	$	(20,563)	$	(8,517)	$	(5,236)

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,
	2015		2014		2013
Federal statutory income tax rate	(34.0)	%	(34.0)	%	(34.0)	%
State taxes, net of federal benefit	(3.8)		(6.6)		(6.6)
Foreign rate differential	6.0		—		—
Research and development tax credits	(1.5)		(1.0)		(1.6)
Change in deferred tax asset valuation allowance	33.3		41.6		42.2
Effective income tax rate	—	%	—	%	—	%

Net deferred tax assets as of December 31, 2015 and 2014 consisted of the following:


		December 31,
	2015		2014
Deferred tax assets:
Net operating loss carryforwards	$	5,750	$	5,606
Capitalized start up costs		4,401		—
Research and development tax credit carryforwards		500		203
Capitalized research and development expenses		611		620
Intangible asset		1,650		—
Stock‑based compensation expenses		373		11
Other		1		4
Total deferred tax assets		13,286		6,444
Deferred tax liabilities:
Other		—		—
Total deferred tax liabilities		—		—
Valuation allowance		(13,286)		(6,444)
Net deferred tax assets	$	—	$	—

As of December 31, 2015, the Company had federal and state net operating loss carryforwards of $13,917 for each, which begin to expire in 2032. As of December 31, 2015, the Company also had federal research and development tax credit carryforwards of $500, which begin to expire in 2032. The Company had no state research and development tax credit carryforwards. The Company also has $490 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, 2015 and 2014. 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, 2015, 2014, and 2013 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,
		2015		2014		2013
Valuation allowance at beginning of year	$	(6,444)	$	(2,899)	$	(690)
Decreases recorded as benefit to income tax provision		—		—		—
Increases recorded to income tax provision		(6,842)		(3,545)		(2,209)
Valuation allowance as of end of year	$	(13,286)	$	(6,444)	$	(2,899)

During 2015, the Company has 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. The following table summarizes the changes in the Company’s unrecognized tax benefits:


	Year ended December 31,
	2015		2014		2013
Unrecognized tax benefits at beginning of year	$	—	$	—	$	—
Increases related to prior year tax provisions		(2,624)		—		—
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, 2015 and 2014. 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, 2015, 2014 and 2013, 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
Related Party Transactions	Dec. 31, 2015
Related Party Transactions
Related Party Transactions	12. Related Party Transactions In September 2012, the Company entered into a sublease agreement for its leased office space in Malvern, Pennsylvania with Ceptaris Therapeutics ("Ceptaris"), a company that was acquired in September 2013. Upon the acquisition, the Company terminated the sublease agreement with Ceptaris and entered into a direct sublease agreement with NeXeption, Inc. ("NeXeption") for the leased space. A member of the Company's board of directors was an executive officer of Ceptaris and is a current executive officer of NeXeption. Total payments made during the years ended December 31, 2015, 2014 and 2013 under these sublease agreements were $124, $66, and $68, respectively (see Note 10). In November 2012, the Company entered into a services agreement with Ceptaris under which Ceptaris provided certain professional services, administrative support and office services to the Company. In September 2013, Ceptaris terminated the agreement in accordance with its terms. In September 2013, the Company entered into a second services agreement with Ceptaris under which Ceptaris provided certain pharmaceutical development and management services to the Company. In December 2013, Ceptaris terminated the agreement in accordance with its terms, effective February 4, 2014. Total payments made to Ceptaris in connection with these agreements during the years ended December 31, 2014 and 2013 were $10 and $166, respectively. In February 2014, the Company entered into a services agreement with NST, LLC (“NST”) under which NST provides certain pharmaceutical development, management and other administrative services to the Company. Certain officers of the Company are also founding partners of NST. Under the same agreement, the Company also provides services to NST and is reimbursed for those services. The Company may offset any payments owed by the Company to NST against payments that are owed by NST to the Company for the provision of NST personnel, including consultants, to the Company. During the year ended December 31, 2015 and 2014, gross expenses incurred by the Company under the services agreement totaled $507 and $467, respectively, and gross expenses charged to NST by the Company totaled $553 and $413, respectively. For the year ended December 31, 2015 and 2014, the Company recorded $161 and $309, respectively, of general and administrative expenses and $207 and $255, respectively, as a reduction of research and development expenses related to these transactions. During the year ended December 31, 2015 and 2014, payments made to NST by the Company totaled $74 and $131, respectively, and receipts received from NST by the Company totaled $120 and $77, respectively. Related to this agreement, no amounts were due to or due from NST at December 31, 2015 or 2014.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References + Details

Agreements Related to Intellectual Property	12 Months Ended
Agreements Related to Intellectual Property	Dec. 31, 2015
Agreements Related to Intellectual Property
Agreements Related to Intellectual Property	13. 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, or 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 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 February 2016 upon the dosing of the first human subject with A-101 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. 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 Accounting Standards Codification 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 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. 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 Accounting Standards Codification 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.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2015
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
401(k) Savings Plan	14. 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 $99, $60 and $51 for the year ended December 31, 2015, 2014 and 2013, respectively.

Quarterly Financial Information (unaudited)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information [Text Block]

15. 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,
2015 Quarter Ended
Revenue	$	—	$	—	$	—	$	—
Operating expenses		2,629		2,596		10,640		4,802
Interest income		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)
2014 Quarter Ended
Revenue	$	—	$	—	$	—	$	—
Operating expenses		1,043		2,226		2,662		2,602
Interest income (expense)		9		(3)		5		5
Net loss		(1,034)		(2,229)		(2,657)		(2,597)
Net loss attributable to common stockholders	$	(1,484)	$	(2,693)	$	(3,136)	$	(3,258)
Net loss per share attributable to common stockholders, basic and diluted	$	(0.95)	$	(1.61)	$	(1.75)	$	(1.76)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2015

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

Patent Application Costs

Patent Costs

Income Taxes

Accretion of Convertible Preferred Stock

Comprehensive Loss

Net Loss per Share

Cash Equivalents

Marketable Securities

Assets Held For Sale, Policy [Policy Text Block]

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

Recently Issued and Adopted Accounting Pronouncements

Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value of Financial Assets and Liabilities

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


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


	Fair Value Measurements as of December 31,
	2014 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	10,012	$	—	$	—	$	10,012
Marketable securities		—		5,891		—		5,891
	$	10,012	$	5,891	$	—	$	15,903

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


	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


	December 31, 2014
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gain		Loss		Value
Marketable securities:
Corporate debt securities	$	5,096	$	—	$	(6)	$	5,090
U.S. government agency debt securities		801		—		—		801
Total marketable securities	$	5,897	$	—	$	(6)	$	5,891

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2015

Property and Equipment, Net

Schedule of property and equipment, net


	December 31,
	2015		2014
Computer equipment	$	262	$	36
Manufacturing equipment		101		—
Construction in progress		—		506
Furniture and fixtures		39		—
		402		542
Less: Accumulated depreciation		(42)		(27)
	$	360	$	515

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2015

Accrued Expenses

Schedule of accrued expenses


	December 31,
	2015		2014
Clinical trial expenses	$	123	$	163
Licensing fees		250		—
Professional fees		283		—
Other		89		25
	$	745	$	188

Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2015

Convertible Preferred Stock.

Schedule of convertible preferred stock


	December 31, 2014
		Preferred					Common
	Preferred	Shares					Stock Issuable
	Shares	Issued and	Carrying		Liquidation		Upon
	Authorized	Outstanding	Value		Preference		Conversion
Series A redeemable convertible preferred stock	20,890,000	20,890,000	$	24,879	$	25,023	6,055,060
Series B redeemable convertible preferred stock	13,200,000	6,451,057		11,798		10,859	1,869,859
	34,090,000	27,341,057	$	36,677	$	35,882	7,924,919

Stockholders' Equity (Deficit) (Tables)

12 Months Ended

Dec. 31, 2015

Stockholders' Equity (Deficit)

Summary of restricted stock activity


		Weighted
		Average Grant
	Number	Date Fair Value
	of Shares	Per Share
Unvested restricted common stock as of December 31, 2013	1,239,247	$	0.00001
Vested	(479,709)	$	0.00001
Unvested restricted common stock as of December 31, 2014	759,538	$	0.00001
Vested	(759,538)	$	0.00001
Unvested restricted common stock as of December 31, 2015	—	$	0.00001

Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2015

Stock-Based Awards

Assumptions used to determine fair value of stock options granted


	Year Ended		Year Ended
	December 31, 2015		December 31, 2014

Risk-free interest rate	1.78	%	1.87	%
Expected term (in years)	6.3		6.4
Expected volatility	93.9	%	113.9	%
Expected dividend yield	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 January 1, 2013	—			—	—		—
Granted	—			—
Exercised	—			—
Forfeited and canceled	—			—
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
Options vested and expected to vest as of December 31, 2015	1,738,524		$	13.23	9.51	$	24,722
Options exercisable as of December 31, 2015	147,672	(1)	$	1.19	8.72	$	3,803

(1)

Summary of RSU activity


		Weighted
		Average
		Grant Date
	Number	Fair Value
	of Shares	Per Share
Outstanding at December 31, 2014	—	$	—
Granted	53,800		28.68
Vested	—		—
Forfeited and cancelled	—		—
Outstanding at December 31, 2015	53,800	$	28.68

Stock-based compensation expense


	Year Ended
	December 31,
	2015		2014		2013
Research and development	$	257	$	10	$	—
General and administrative		634		17		—
	$	891	$	27	$	—

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2015

Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders


	Year Ended
	December 31,
	2015		2014		2013
Numerator:
Net loss	$	(20,563)	$	(8,517)	$	(5,236)
Accretion of redeemable convertible preferred stock to redemption value		(2,566)		(2,054)		(1,740)
Net loss attributable to common stockholders	$	(23,129)	$	(10,571)	$	(6,976)
Denominator:
Weighted average shares of common stock outstanding		6,637,678		2,730,427		2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding		(530,636)		(1,010,345)		(1,649,080)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted		6,107,042		1,720,082		1,081,347
Net loss per share attributable to common stockholders, basic and diluted	$	(3.79)	$	(6.15)	$	(6.45)

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


	Year Ended December 31,
	2015	2014	2013

Stock options to purchase common stock	1,738,524	500,262	—
Restricted stock unit awards	53,800	—	—
Unvested restricted common stock	—	759,538	1,239,247
Convertible preferred stock (as converted to common stock)	—	7,924,919	6,055,060
	1,792,324	9,184,719	7,294,307

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2015

Commitments and Contingencies

Schedule of future minimum lease payments under the sublease


Years Ending December 31,
2016	$	237
2017		263
2018		268
2019		251
2020		—
Total	$	1,019

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Taxes

Schedule of loss before income taxes by jurisdiction


	Year Ended December 31,
	2015		2014		2013
U.S. operations	$	(11,823)	$	(8,517)	$	(5,236)
Foreign operations		(8,740)		—		—
Loss before income taxes	$	(20,563)	$	(8,517)	$	(5,236)

Reconciliation of statutory to effective rate


	Year Ended December 31,
	2015		2014		2013
Federal statutory income tax rate	(34.0)	%	(34.0)	%	(34.0)	%
State taxes, net of federal benefit	(3.8)		(6.6)		(6.6)
Foreign rate differential	6.0		—		—
Research and development tax credits	(1.5)		(1.0)		(1.6)
Change in deferred tax asset valuation allowance	33.3		41.6		42.2
Effective income tax rate	—	%	—	%	—	%

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


		December 31,
	2015		2014
Deferred tax assets:
Net operating loss carryforwards	$	5,750	$	5,606
Capitalized start up costs		4,401		—
Research and development tax credit carryforwards		500		203
Capitalized research and development expenses		611		620
Intangible asset		1,650		—
Stock‑based compensation expenses		373		11
Other		1		4
Total deferred tax assets		13,286		6,444
Deferred tax liabilities:
Other		—		—
Total deferred tax liabilities		—		—
Valuation allowance		(13,286)		(6,444)
Net deferred tax assets	$	—	$	—

Changes in deferred tax asset valuation allowance


		Year Ended December 31,
		2015		2014		2013
Valuation allowance at beginning of year	$	(6,444)	$	(2,899)	$	(690)
Decreases recorded as benefit to income tax provision		—		—		—
Increases recorded to income tax provision		(6,842)		(3,545)		(2,209)
Valuation allowance as of end of year	$	(13,286)	$	(6,444)	$	(2,899)

Schedule of Changes in Unrecognized Tax Benefits


	Year ended December 31,
	2015		2014		2013
Unrecognized tax benefits at beginning of year	$	—	$	—	$	—
Increases related to prior year tax provisions		(2,624)		—		—
Increases related to current year tax provisions		(1,776)		—		—
Unrecognized tax benefits as of end of year	$	(4,400)	$	—	$	—

Quarterly Financial Information (unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]


	March 31,		June 30,		September 30,		December 31,
2015 Quarter Ended
Revenue	$	—	$	—	$	—	$	—
Operating expenses		2,629		2,596		10,640		4,802
Interest income		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)
2014 Quarter Ended
Revenue	$	—	$	—	$	—	$	—
Operating expenses		1,043		2,226		2,662		2,602
Interest income (expense)		9		(3)		5		5
Net loss		(1,034)		(2,229)		(2,657)		(2,597)
Net loss attributable to common stockholders	$	(1,484)	$	(2,693)	$	(3,136)	$	(3,258)
Net loss per share attributable to common stockholders, basic and diluted	$	(0.95)	$	(1.61)	$	(1.75)	$	(1.76)

Organization and Nature of Business - IPO, Stock Split, Liquidity (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Oct. 13, 2015 USD ($) $ / shares shares	Sep. 24, 2015	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Initial public offering
Aggregate gross proceeds			$ 56,550
Common stock shares issued upon conversion of convertible preferred stock \| shares	11,677,076
Payments of initial public offering costs			2,272
Reverse stock split		0.2899
Accumulated deficit			42,833	$ 20,749
Cash, cash equivalents and marketable securities			92,038
Proceeds from initial public offering, net of offering costs			$ 56,550
IPO
Initial public offering
Number of shares issued in offering \| shares	5,000,000
Issuance price (in dollars per share) \| $ / shares	$ 11.00
Aggregate gross proceeds	$ 55,000
Payments of initial public offering costs	2,272
Offering proceeds, net of discounts, commissions and expenses	$ 56,550
Exercise of over-allotment option
Initial public offering
Number of shares issued in offering \| shares	750,000
Issuance price (in dollars per share) \| $ / shares	$ 11.00
Aggregate gross proceeds	$ 8,250
Payments of initial public offering costs	$ 4,428

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Write-down of property and equipment held for sale	$ 289
Assets held for sale	216
Deferred offering costs
Offering costs offset against additional paid in capital	0	$ 0
Research and Development Caption [Member]
Write-down of property and equipment held for sale	$ 289
Computer equipment
Property and Equipment, Net
Depreciation period (in years)	3 years
Manufacturing equipment
Write-down of property and equipment held for sale	$ 289
Property and Equipment, Net
Depreciation period (in years)	5 years
Furniture and Fixtures [Member]
Property and Equipment, Net
Depreciation period (in years)	7 years

Fair Value of Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Assets:
Marketable securities	$ 82,187	$ 5,891
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	9,060	10,012
Marketable securities	82,187	5,891
Total assets measured at fair value	91,247	15,903
Recurring \| Level 1
Assets:
Cash equivalents	8,810	10,012
Total assets measured at fair value	8,810	10,012
Recurring \| Level 2
Assets:
Cash equivalents	250
Marketable securities	82,187	5,891
Total assets measured at fair value	$ 82,437	$ 5,891

Fair Value of Financial Assets and Liabilities - by type (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Marketable securities:
Amortized Cost	$ 82,341	$ 5,897
Gross Unrealized Loss	(154)	(6)
Fair Value	82,187	5,891
Corporate debt securities
Marketable securities:
Amortized Cost	46,270	5,096
Gross Unrealized Loss	(125)	(6)
Fair Value	$ 46,145	$ 5,090
Corporate debt securities \| Maximum
Marketable securities:
Remaining term of maturities (in months)	15 months	13 months
Commercial paper
Marketable securities:
Amortized Cost	$ 9,789
Fair Value	9,789
Asset-backed Securities [Member]
Marketable securities:
Amortized Cost	6,234
Gross Unrealized Loss	(14)
Fair Value	6,220
U.S. government agency debt securities
Marketable securities:
Amortized Cost	20,048	$ 801
Gross Unrealized Loss	(15)
Fair Value	$ 20,033	$ 801

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property and Equipment, net
Property and equipment	$ 402	$ 542
Less: accumulated depreciation	(42)	(27)
Property and equipment, net	360	515
Depreciation expense	90	12	$ 11
Write-down of property and equipment held for sale	289
Computer equipment
Property and Equipment, net
Property and equipment	262	36
Manufacturing equipment
Property and Equipment, net
Property and equipment	101
Write-down of property and equipment held for sale	289
Construction in progress
Property and Equipment, net
Property and equipment		$ 506
Furniture and Fixtures [Member]
Property and Equipment, net
Property and equipment	$ 39

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accrued Expenses
Clinical trial expenses	$ 123	$ 163
Licensing fees	250
Professional fees	283
Other	89	25
Accrued expenses, total	$ 745	$ 188

Convertible Preferred Stock (Details) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Oct. 13, 2015 shares	Aug. 28, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) Milestone director $ / shares shares	Dec. 31, 2015 USD ($) installment director $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Convertible Preferred Stock
Authorized (in shares)					34,090,000
Par value (in dollars per share) \| $ / shares					$ 0.00001
New issues (in shares)				12,944,984	6,451,057
Issuance of convertible preferred stock \| $				$ 39,864	$ 11,623
Temporary equity, issuance costs \| $				$ 136	60
Fair value of preferred stock purchased put option on date of issuance \| $					$ 1,039
Fair value assumptions
Preferred Shares Issued and Outstanding					27,341,057
Carrying Value \| $					$ 36,677	$ 23,000	$ 21,260
Liquidation Preference \| $					$ 35,882
Common Stock Issuable Upon Conversion					7,924,919
Dividends
Dividend rate, as a percent				8.00%
Conversion
Minimum net proceeds received in qualified public offering requiring mandatory conversion of temporary equity \| $				$ 40,000
Minimum share price in qualified public offering requiring mandatory conversion of temporary equity (in dollars per share) \| $ / shares				$ 12.80
Minimum percentage of holders required for determination of conversion date				60.00%
Conversion ratio					3.45
Common stock shares issued upon conversion of convertible preferred stock	11,677,076
Redemption
Minimum percentage of holders required for redemption				60.00%
Number of redemption installments \| installment				3
Period before redemption				60 days
Number of Directors entitled to elect \| director				3
Conversion of Stock, Shares Issued	11,677,076
Preferred Stock, Shares Authorized				10,000,000	0
Preferred Stock, Shares Outstanding				0
Series A convertible preferred stock
Convertible Preferred Stock
Authorized (in shares)					20,890,000
Issue price of shares (in dollars per share) \| $ / shares				$ 1.00
Fair value assumptions
Preferred Shares Issued and Outstanding					20,890,000
Carrying Value \| $					$ 24,879
Liquidation Preference \| $					$ 25,023
Common Stock Issuable Upon Conversion					6,055,060
Conversion
Conversion price (in dollars per share) \| $ / shares				3.45
Series B convertible preferred stock
Convertible Preferred Stock
Authorized (in shares)					13,200,000
New issues (in shares)			6,451,057
Issue price of shares (in dollars per share) \| $ / shares			$ 1.65
Issuance of convertible preferred stock \| $			$ 10,644
Temporary equity, issuance costs \| $			$ 60
Fair value assumptions
Preferred Shares Issued and Outstanding					6,451,057
Carrying Value \| $					$ 11,798
Liquidation Preference \| $					$ 10,859
Common Stock Issuable Upon Conversion					1,869,859
Conversion
Conversion price (in dollars per share) \| $ / shares				5.6925
Series B convertible preferred stock \| Put option \| Long position
Convertible Preferred Stock
Number of milestones to attain for call of purchased put option \| Milestone			2
Number of shares that may be exercised under option			6,451,057
Price at which shares may be exercised under option (in dollars per share) \| $ / shares			$ 1.65
Number of directors for confirming exercise of option \| director			5
Percentage of voting stockholders for confirming exercise of option			60.00%
Fair value of preferred stock purchased put option on date of issuance \| $			$ 1,039
Fair value assumptions
Risk-free interest rate assumption (as a percent)			0.08%
Expected term (in months)			9 months
Expected volatility (as a percent)			80.00%
Expected dividends \| $ / shares			$ 0
Fair value of underlying instruments (as a percent) \| $ / shares			$ 1.65
Probability of occurrence of successful attainment of specified milestones triggering exercise of option (as a percent)			60.00%
Probability of occurrence of option exercised when exercisable (as a percent)			60.00%
Series C convertible preferred stock
Convertible Preferred Stock
New issues (in shares)		12,944,984
Issue price of shares (in dollars per share) \| $ / shares		$ 3.09
Issuance of convertible preferred stock \| $		$ 40,000
Conversion
Conversion price (in dollars per share) \| $ / shares				$ 10.6605

Stockholders' Equity (Deficit) - Common Stock (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) Vote $ / shares shares	Dec. 31, 2014 $ / shares shares
Stockholders' Equity (Deficit)
Common stock shares authorized \| shares	100,000,000	77,000,000
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 (Deficit) - Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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
Number of Shares
Number of shares, beginning balance		759,538	1,239,247
Number of shares, Vested		(759,538)	(479,709)
Number of shares, ending balance			759,538	1,239,247
Weighted Average Grant Date Fair Value Per Share
Weighted average grant date fair value, beginning balance (in dollars per share)		$ 0.00001	$ 0.00001
Weighted average grant date fair value, vested (in dollars per share)		0.00001	0.00001
Weighted average grant date fair value, ending balance (in dollars per share)		$ 0.00001	$ 0.00001	$ 0.00001
Aggregate fair value of restricted stock awards vested during the year		$ 6,423	$ 448	$ 281
Number of restricted stock shares subject to repurchase		0	759,538
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) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Sep. 15, 2015	Aug. 25, 2015
Stock-based awards
Options granted (in shares)	1,238,262	500,262
Number of Shares
Number of Shares, beginning balance	500,262
Number of Shares, Granted	1,238,262	500,262
Number of Shares, ending balance	1,738,524	500,262
Number of Shares, Options vested and expected to vest	1,738,524
Number of Shares, Options exercisable	147,672
Weighted Average Exercise Price
Weighted Average Exercise Price, beginning balance (in dollars per share)	$ 1.22
Weighted Average Exercise Price, Granted (in dollars per share)	18.08	$ 1.22
Weighted Average Exercise Price, ending balance (in dollars per share)	13.23	$ 1.22
Weighted Average Exercise Price, Options vested and expected to vest (in dollars per share)	13.23
Weighted Average Exercise Price, Options exercisable (in dollars per share)	$ 1.19
Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term (in years)	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 6 months 4 days
Weighted Average Remaining Contractual Term, Options exercisable (in years)	8 years 8 months 19 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 24,722	$ 305
Aggregate Intrinsic Value, Options vested and expected to vest	24,722
Aggregate Intrinsic Value, Options exercisable	$ 3,803
Weighted average grant-date fair value of stock options granted (in dollars per share)	$ 13.84	$ 1.38
Employee, director and consultant stock options
Stock-based awards
Options granted (in shares)			0
Stock Option Valuation
Risk-free interest rate (as a percent)	1.78%	1.87%
Expected term (in years)	6 years 3 months 18 days	6 years 4 months 24 days
Expected volatility (as a percent)	93.90%	113.90%
Expected dividend yield (as a percent)	0.00%	0.00%
Expected forfeiture rate (as a percent)	0.00%	0.00%
Number of Shares
Number of Shares, Granted			0
2012 Equity Compensation Plan
Stock-based awards
Number of shares authorized		500,262			1,539,169
Number of shares available for grant	0
2012 Equity Compensation Plan \| Maximum
Stock-based awards
Term of award (in years)	10 years
2012 Equity Compensation 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%
Term of award (in years)	10 years
Vesting period (in years)	4 years
2015 Equity Incentive Plan
Stock-based awards
Number of shares authorized				2,784,395
Percentage increase to shares available for grant from common outstanding as of preceding December 31 (as a percent)				4.00%

Stock-Based Awards - RSUs (Details) - $ / shares	1 Months Ended	12 Months Ended
Stock-Based Awards - RSUs (Details) - $ / shares	Jul. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Weighted Average Grant Date Fair Value Per Share
Weighted average grant date fair value, beginning balance (in dollars per share)		$ 0.00001	$ 0.00001
Granted, estimated grant-date fair value (in dollars per share)	$ 0.00001
Weighted average grant date fair value, ending balance (in dollars per share)		$ 0.00001	$ 0.00001	$ 0.00001
Weighted average period unrecognized stock-based compensation cost to be recognized (in years)		3 years 6 months 4 days
Restricted Stock Units (RSUs) [Member]
RSU Activity
Granted		53,800
Units outstanding, end of period		53,800
Weighted Average Grant Date Fair Value Per Share
Granted, estimated grant-date fair value (in dollars per share)		$ 28.68
Weighted average grant date fair value, ending balance (in dollars per share)		$ 28.68
2015 Equity Incentive Plan \| Restricted Stock Units (RSUs) [Member]
RSU Activity
Granted			0	0

Stock-Based Awards - Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Stock-based compensation expense
Stock-based compensation expense	$ 891	$ 27
Unrecognized stock-based compensation cost	$ 19,093
Weighted average period unrecognized stock-based compensation cost to be recognized (in years)	3 years 6 months 4 days
Research and development expense.
Stock-based compensation expense
Stock-based compensation expense	$ 257	10
General and administrative expense.
Stock-based compensation expense
Stock-based compensation expense	$ 634	$ 17

Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net loss	$ (4,714)	$ (10,632)	$ (2,594)	$ (2,623)	$ (2,597)	$ (2,657)	$ (2,229)	$ (1,034)	$ (20,563)	$ (8,517)	$ (5,236)
Accretion of convertible preferred stock to redemption value									(2,566)	(2,054)	(1,740)
Net loss attributable to common stockholders	$ (4,927)	$ (11,652)	$ (3,270)	$ (3,280)	$ (3,258)	$ (3,136)	$ (2,693)	$ (1,484)	$ (23,129)	$ (10,571)	$ (6,976)
Denominator:
Weighted average shares of common stock outstanding (in shares)									6,637,678	2,730,427	2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding (in shares)									(530,636)	(1,010,345)	(1,649,080)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted (in shares)									6,107,042	1,720,082	1,081,347
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.28)	$ (5.12)	$ (1.52)	$ (1.61)	$ (1.76)	$ (1.75)	$ (1.61)	$ (0.95)	$ (3.79)	$ (6.15)	$ (6.45)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Net Loss per Share - Anti-dilution (Details) - shares	12 Months Ended
Net Loss per Share - Anti-dilution (Details) - shares	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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	1,792,324	9,184,719	7,294,307
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	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	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	1,239,247
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	6,055,060

Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	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
Director \| Direct sublease agreement
Lease
Expenses incurred under related party transactions	119	$ 66
Future minimum lease payments under the sublease
2016	237
2017	263
2018	268
2019	251
Total	$ 1,019

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Loss before income taxes
U.S. operations									$ (11,823)	$ (8,517)	$ (5,236)
Foreign operations									(8,740)
Net loss	$ (4,714)	$ (10,632)	$ (2,594)	$ (2,623)	$ (2,597)	$ (2,657)	$ (2,229)	$ (1,034)	$ (20,563)	$ (8,517)	$ (5,236)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate									(34.00%)	(34.00%)	(34.00%)
State taxes, net of federal benefit									(3.80%)	(6.60%)	(6.60%)
Foreign rate differential									6.00%
Research and development tax credits									(1.50%)	(1.00%)	(1.60%)
Change in deferred tax asset valuation allowance									33.30%	41.60%	42.20%
Components of net deferred tax assets
Net operating loss carryforwards												$ 5,750	$ 5,606
Capitalized start-up costs												4,401
Research and development tax credit carryforwards												500	203
Capitalized research and development expenses												611	620
Intangible assets												1,650
Stock‑based compensation expenses												373	11
Other												1	4
Total deferred tax assets												13,286	6,444
Valuation allowance	(13,286)			(6,444)	(6,444)			(2,899)	$ (6,444)	$ (2,899)	$ (690)	(13,286)	(6,444)
Changes in valuation allowance for deferred tax assets
Valuation allowance at beginning of year				$ (6,444)				$ (2,899)	(6,444)	(2,899)	(690)
Increases recorded to income tax provision									(6,842)	(3,545)	(2,209)
Valuation allowance as of end of year	(13,286)				$ (6,444)				(13,286)	$ (6,444)	$ (2,899)
Unrecognized Tax Benefits
Increases related to prior year tax provisions									(2,624)
Increases related to current year tax provisions									(1,776)
Unrecognized Tax Benefits, Ending Balance	$ (4,400)								(4,400)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate												0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense									$ 0
Federal
Components of net deferred tax assets
Net operating loss carryforwards												13,917
Research and development tax credit carryforwards												500
State
Components of net deferred tax assets
Net operating loss carryforwards												13,917
Research and development tax credit carryforwards												$ 0

Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Director \| Direct sublease agreement
Related Party Transactions
Expenses incurred under related party transactions	$ 119	$ 66
Director \| Direct sublease agreement \| Ceptaris Therapeutics [Member]
Related Party Transactions
Expenses incurred under related party transactions	124	66	$ 68
Director \| Services agreement \| Ceptaris Therapeutics [Member]
Related Party Transactions
Expenses incurred under related party transactions		10	166
Certain officers \| Services agreement \| NST, LLC [Member]
Related Party Transactions
Expenses incurred under related party transactions	507	467
Amounts due to or from related party	0	0	$ 0
Other revenue earned from related party transactions	553	413
Payments to related party	74	131
Receipts from related party	120	77
Certain officers \| Services agreement \| NST, LLC [Member] \| General and administrative expense.
Related Party Transactions
Net expenses (revenues) from related party transactions	161	309
Certain officers \| Services agreement \| NST, LLC [Member] \| Research and development expense.
Related Party Transactions
Net expenses (revenues) from related party transactions	$ (207)	$ (255)

Agreements Related to Intellectual Property (Details) - USD ($) $ in Thousands		1 Months Ended			12 Months Ended
	Aug. 27, 2015	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
License Agreement
Upfront payment recorded as research and development expense					$ 15,339	$ 6,507	$ 3,488
Assignment Agreement and Finder's Services Agreement [Member] \| A-101
License Agreement
Milestone payment		$ 300					$ 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 Agreeement, Minimum				15 years
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 \| 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, 2015	Dec. 31, 2014	Dec. 31, 2013
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	$ 99	$ 60	$ 51

Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Operating Expenses	$ 4,802	$ 10,640	$ 2,596	$ 2,629	$ 2,602	$ 2,662	$ 2,226	$ 1,043	$ 20,667	$ 8,533	$ 5,257
Interest income	89	7	2	6	5	5	(3)	9	104	16	21
Net loss	(4,714)	(10,632)	(2,594)	(2,623)	(2,597)	(2,657)	(2,229)	(1,034)	(20,563)	(8,517)	(5,236)
Net loss attributable to common stockholders	$ (4,927)	$ (11,652)	$ (3,270)	$ (3,280)	$ (3,258)	$ (3,136)	$ (2,693)	$ (1,484)	$ (23,129)	$ (10,571)	$ (6,976)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.28)	$ (5.12)	$ (1.52)	$ (1.61)	$ (1.76)	$ (1.75)	$ (1.61)	$ (0.95)	$ (3.79)	$ (6.15)	$ (6.45)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Organization and Nature of Business (Details)	Dec. 31, 2015 item
A-101
Production information
Number of clinical trials completed	3