Document and Entity Information	9 Months Ended
Document and Entity Information	Sep. 30, 2015	Nov. 17, 2015
Document and Entity Information
Entity Registrant Name	Aclaris Therapeutics, Inc.
Entity Central Index Key	0001557746
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		20,157,503
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3

CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 25,419	$ 10,757
Marketable securities	12,986	5,373
Prepaid expenses and other current assets	955	204
Total current assets	39,360	16,334
Marketable securities		518
Property and equipment, net	761	515
Deferred offering costs	1,943
Other assets	23	10
Total assets	42,087	17,377
Current liabilities:
Accounts payable	958	1,263
Accrued expenses	939	188
Total current liabilities	1,897	1,451
Deferred rent	3	4
Total liabilities	1,900	1,455
Convertible preferred stock (Series A, B and C), $0.00001 par value; 40,286,041 and 34,090,000 shares authorized at September 30, 2015 and December 31, 2014, respectively; 40,286,041 and 27,341,057 shares issued and outstanding at September 30, 2015 and December 31, 2014, respectively; aggregate liquidation preference of $78,282 and $35,882 at September 30, 2015 and December 31, 2014, respectively	78,305	36,677
Stockholders' deficit:
Common stock, $0.00001 par value; 110,000,000 and 77,000,000 shares authorized at September 30, 2015 and December 31, 2014, respectively; 2,730,427 and 2,730,427 shares issued and outstanding
Additional paid-in capital
Accumulated other comprehensive income (loss)	1	(6)
Accumulated deficit	(38,119)	(20,749)
Total stockholders' deficit	(38,118)	(20,755)
Total liabilities, convertible preferred stock and stockholders' deficit	$ 42,087	$ 17,377

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2015	Dec. 31, 2014
Condensed Consolidated Balance Sheets (Unaudited)
Convertible preferred stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Convertible preferred stock, shares authorized	40,286,041	34,090,000
Convertible preferred stock, shares issued	40,286,041	27,341,057
Convertible preferred stock, shares outstanding	40,286,041	27,341,057
Liquidation Preference	$ 78,282	$ 35,882
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized	110,000,000	77,000,000
Common stock, shares issued	2,730,427	2,730,427
Common stock, shares outstanding	2,730,427	2,730,427

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Consolidated Statements Of Operations And Comprehensive Loss (Unaudited)
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	9,408	2,097	12,937	4,453
General and administrative	1,232	565	2,928	1,478
Total operating expenses	10,640	2,662	15,865	5,931
Loss from operations	(10,640)	(2,662)	(15,865)	(5,931)
Interest income	7	5	16	11
Net loss	(10,633)	(2,657)	(15,849)	(5,920)
Accretion of convertible preferred stock	(995)	(479)	(2,353)	(1,394)
Net loss attributable to common stockholders	(11,628)	(3,136)	(18,202)	(7,314)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (5.11)	$ (1.75)	$ (8.44)	$ (4.36)
Weighted average common shares outstanding, basic and diluted (in shares)	2,274,617	1,794,909	2,155,685	1,675,976
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities, net of tax of $0	1	(3)	7	(3)
Total other comprehensive income (loss)	1	(3)	7	(3)
Comprehensive loss	$ (10,632)	$ (2,660)	$ (15,842)	$ (5,923)

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Consolidated Statements Of Operations And Comprehensive Loss (Unaudited)
Unrealized gain (loss) on marketable securities, tax	$ 0	$ 0	$ 0	$ 0

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT (UNAUDITED) (USD $) In Thousands, except Share data, unless otherwise specified	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balance at Dec. 31, 2014			$ (6)	$ (20,749)	$ (20,755)
Balance at Dec. 31, 2014					36,677
Balance (in shares) at Dec. 31, 2014	2,730,427				2,730,427
Balance (in shares) at Dec. 31, 2014					27,341,057
Increase (Decrease) in Temporary Equity
Issuance of Series C convertible preferred stock, net of issuance costs of $136					39,864
Issuance of Series C convertible preferred stock, net of issuance costs of $136 (in shares)					12,944,984
Accretion of convertible preferred stock to redemption value					1,764
Increase (Decrease) in Stockholders' Equity
Unrealized gain on marketable securities			7		7
Stock-based compensation expense		243			243
Accretion of convertible preferred stock to redemption value		(243)		(1,521)	(1,764)
Net loss				(15,849)	(15,849)
Balance at Sep. 30, 2015			1	(38,119)	(38,118)
Balance at Sep. 30, 2015					$ 78,305
Balance (in shares) at Sep. 30, 2015	2,730,427				2,730,427
Balance (in shares) at Sep. 30, 2015					40,286,041

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net loss	$ (15,849)	$ (5,920)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	57	9
Stock-based compensation expense	243	8
Deferred rent	(1)	1
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(764)	(397)
Accounts payable	(491)	920
Accrued expenses	573	505
Net cash used in operating activities	(16,232)	(4,874)
Cash flows from investing activities:
Purchases of property and equipment	(375)	(148)
Purchases of marketable securities	(13,002)
Proceeds from sales and maturities of marketable securities	5,914	3,734
Net cash (used in) provided by investing activities	(7,463)	3,586
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	39,864	10,588
Payments of initial public offering costs	(1,507)
Net cash provided by financing activities	38,357	10,588
Net increase in cash and cash equivalents	14,662	9,300
Cash and cash equivalents at beginning of period	10,757	9,588
Cash and cash equivalents at end of period	25,419	18,888
Supplemental disclosures of non-cash investing and financing activities:
Additions to property and equipment purchases included in accounts payable	19	8
Accretion of convertible preferred stock to redemption value	1,764	1,393
Fair value of preferred stock purchased put option on date of issuance		1,039
Deferred offering costs included in accounts payable and accrued expenses	$ 436

Organization and Nature of Business	9 Months Ended
Organization and Nature of Business	Sep. 30, 2015
Organization and Nature of Business
Organization and Nature of Business	1. Organization and Nature of Business Aclaris Therapeutics, Inc. (the “Company”) was incorporated under the laws of the State of Delaware in 2012. 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. On July 17, 2015, Aclaris Therapeutics International Limited was established as a wholly-owned subsidiary of the Company. 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 shares 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. 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’s 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 to the underwriters underwriting discounts and commissions of $4,428 in connection with the IPO, including the underwriters’ exercise of their option to purchase additional shares. In addition, the Company incurred expenses of approximately $2,200 in connection with the IPO. Thus, the net offering proceeds to the Company, after deducting underwriting discounts and commissions and offering expenses, were $56,623. 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 convertible preferred stock (see Note 6). Accordingly, all share and per share amounts for all periods presented in these 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 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 September 30, 2015, the Company had working capital of $37,463, an accumulated deficit of $38,119 and cash, cash equivalents and marketable securities of $38,405. Upon consummation of its IPO on October 13, 2015, the Company received cash proceeds, net of underwriting discounts and commissions, of $58,823. 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 and cash equivalents as of September 30, 2015, together with the proceeds received in connection with its IPO in October 2015, will be sufficient to fund its operations for at least the next 24 months. 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.

- Definition

The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.

+ References+ Details

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2015
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed 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, Aclaris Therapeutics International Limited. 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, the accrual of research and development expenses and the valuation of common stock and 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. Unaudited Interim Financial Information The accompanying condensed consolidated balance sheet as of September 30, 2015, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2015 and 2014, the condensed consolidated statement of convertible preferred stock and stockholders’ deficit for the nine months ended September 30, 2015, and the condensed consolidated statements of cash flows for the nine months ended September 30, 2015 and 2014 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2015, the results of its operations and comprehensive loss for the three and nine months ended September 30, 2015 and 2014 and its cash flows for the nine months ended September 30, 2015 and 2014. The financial data and other information disclosed in these notes related to the nine months ended September 30, 2015 and 2014 are unaudited. The results for the nine months ended September 30, 2015 are not necessarily indicative of results to be expected for the year ending December 31, 2015, any other interim periods, or any future year or period. The unaudited interim financial statements of the Company included herein have been prepared, pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto for the year ended December 31, 2014 included in the Company’s final prospectus filed on October 8, 2015 with the SEC pursuant to Rule 424(b)(4) of the Securities Act of 1933, as amended (the “Securities Act”). Significant Accounting Policies The Company’s significant accounting policies are disclosed in the audited financial statements for the year ended December 31, 2014 included in the Company’s final prospectus filed on October 8, 2015 with the SEC pursuant to the Securities Act. Since the date of such financial statements, there have been no changes to the Company’s significant accounting policies, other than those detailed below. 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’ deficit as a reduction of additional paid-in capital generated as a result of the offering. As of September 30, 2015, the Company had recorded $1,943 of deferred offering costs incurred in connection with the IPO. The deferred offering costs were offset against the net proceeds received upon completion of the IPO in October 2015.

Fair Value of Financial Assets and Liabilities

9 Months Ended

Sep. 30, 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 September 30, 2015 Using:
	Level 1		Level 2		Level 3		Total

Assets:
Cash equivalents	$	25,020	$	—	$	—	$	25,020
Marketable securities	—		12,986		—		12,986

	$	25,020	$	12,986	$	—	$	38,006

	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 September 30, 2015 and December 31, 2014, the Company’s cash equivalents, which were invested in money market funds, were valued based on Level 1 inputs. In determining the fair value of its corporate debt securities and U.S. government agency debt securities as of September 30, 2015 and December 31, 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 nine months ended September 30, 2015 and the years ended December 31, 2014, there were no transfers between Level 1, Level 2 and Level 3.

As of September 30, 2015 and December 31, 2014, the fair value of the Company’s available-for-sale marketable securities by type of security was as follows:

	September 30, 2015
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
Marketable securities:
Corporate debt securities	$	12,985	$	1	$	—	$	12,986

	$	12,985	$	1	$	—	$	12,986

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

	$	5,897	$	—	$	(6	)	$	5,891

As of September 30, 2015 and December 31, 2014, the Company’s corporate debt securities had credit ratings of A and above and remaining maturities of less than 8 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.

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Property and Equipment, Net

9 Months Ended

Sep. 30, 2015

Property and Equipment, Net

Property and Equipment, Net

4. Property and Equipment, Net

Property and equipment, net consisted of the following:

	September 30, 2015			December 31, 2014
Computer equipment	$	190		$	36
Manufacturing equipment	578			—
Construction in progress	77			506

	845			542
Less: Accumulated depreciation	(84		)	(27		)

	$	761		$	515

Depreciation expense was $32 and $3 for the three months ended September 30, 2015 and 2014, respectively, and $57 and $9 for the nine months ended September 30, 2015 and 2014, respectively. Construction in progress as of September 30, 2015 consisted of manufacturing equipment, which is expected to be placed into service in 2016.

- Definition

The entire disclosure for long-lived, physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, accounting policies and methodology, roll forwards, depreciation, depletion and amortization expense, including composite depreciation, accumulated depreciation, depletion and amortization expense, useful lives and method used, income statement disclosures, assets held for sale and public utility disclosures.

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Accrued Expenses

9 Months Ended

Sep. 30, 2015

Accrued Expenses

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following:

	September 30, 2015		December 31, 2014
Payroll and payroll-related costs	$	463	$	—
Clinical trial expenses	284		163
Deferred offering costs	178		—
Other	14		25

	$	939	$	188

Convertible Preferred Stock

9 Months Ended

Sep. 30, 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 September 30, 2015 and December 31, 2014, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 40,286,041 shares and 34,090,000 shares, respectively, 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. The rights and preferences of the Series C preferred stock were similar to those of the Series A and Series B preferred stock, except that (1) the Original Issue Price for Series C preferred stock was $3.09 per share, (2) the holders of the Series C preferred stock did not have redemption rights, and (3) the holders of the Series C preferred stock had specified protective rights not held by the holders of the Series A and Series B 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 at that time. As a result of the removal of the redemption rights, as of August 25, 2015, the Company ceased the periodic recording of adjustments to accrete 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 three and nine months ended September 30, 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.

Also 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 condensed 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:

	September 30, 2015
	Preferred Shares Authorized	Preferred Shares Issued and Outstanding	Carrying Value		Liquidation Preference		Common Stock Issuable Upon Conversion
Series A convertible preferred stock	20,890,000	20,890,000	$	26,178	$	26,491	6,055,060
Series B convertible preferred stock	6,451,057	6,451,057	12,263		11,496		1,869,859
Series C convertible preferred stock	12,944,984	12,944,984	39,864		40,295		3,752,157

	40,286,041	40,286,041	$	78,305	$	78,282	11,677,076

	December 31, 2014
	Preferred Shares Authorized	Preferred Shares Issued and Outstanding	Carrying Value		Liquidation Preference		Common Stock Issuable Upon Conversion
Series A convertible preferred stock	20,890,000	20,890,000	$	24,879	$	25,023	6,055,060
Series B 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

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 was convertible 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 was $3.45 for Series A preferred stock, $5.6925 for Series B preferred stock and $10.6605 for Series C preferred stock and was subject to adjustment as set forth in the Company’s certificate of incorporation, as amended and restated. As of September 30, 2015 and December 31, 2014, all outstanding shares of Series A and Series B preferred stock were convertible into common stock on a 3.45-for-1 basis.

As previously 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.

Stockholders' Deficit

9 Months Ended

Sep. 30, 2015

Stockholders' Deficit

Stockholders' Deficit

7. Stockholders’ Deficit

Common Stock

As of September 30, 2015 and December 31, 2014, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 110,000,000 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 the preferential dividend rights of the Preferred Stock. When dividends are declared on shares of common stock, the Company must declare at the same time a dividend payable to the holders of Preferred Stock equivalent to the dividend amount they would receive if each preferred share were converted into common stock. The Company may not pay dividends to common stockholders until all dividends accrued or declared but unpaid on the Preferred Stock have been paid in full. No dividends had been declared through September 30, 2015.

As of September 30, 2015 and December 31, 2014, the Company had reserved 13,216,245 shares and 8,425,181 shares of common stock, respectively, for the conversion of the outstanding shares of Series A, Series B and Series C preferred stock (see Note 6) and the exercise of outstanding stock options and the number of shares remaining available for future grant under the Company’s 2012 Plan (see Note 8).

Restricted Common Stock

The Company has granted restricted common stock with time-based vesting conditions. Unvested shares of restricted common stock may not be sold or transferred by the holder. These restrictions lapse according to the time-based vesting conditions of each award. Upon a qualified public offering or a change in control of the Company, all unvested shares of restricted common stock vest 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 September 30, 2015 and December 31, 2014, 399,757 shares and 759,538 shares, respectively, were subject to repurchase.

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

	Number of Shares	Weighted Average Grant Date Fair Value Per Share
Unvested restricted common stock as of December 31, 2014	759,538	$	0.00001
Vested	359,781	$	0.00001

Unvested restricted common stock as of September 30, 2015	399,757	$	0.00001

The aggregate intrinsic value of restricted stock awards that vested during the three months ended September 30, 2015 and 2014 and the nine months ended September 30, 2015 and 2014 was $1,091, $170, $2,026 and $269, respectively.

As previously discussed in Note 1, the Company completed its IPO in October 2015. As a result of the IPO, all of the Company’s remaining unvested restricted common stock vested in full.

- 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 SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 4

-Section C

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 4

-Section E

Reference 3: 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 4: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 505

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-Paragraph 4

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-Name Accounting Standards Codification

-Topic 210

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.29-31)

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Glossary Preferred Stock

-URI http://asc.fasb.org/extlink&oid=6521494

Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74512-122707

+ Details

Stock-Based Awards

9 Months Ended

Sep. 30, 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 of September 30, 2015 and December 31, 2014, 398,645 and 0 shares remained available for grant under the 2012 Plan, respectively.

As required by the 2012 Plan, the exercise price for stock options granted is not to be less than the fair value of common shares as determined by the Company as of the date of grant. The Company values 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.

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, performance stock awards, cash-based awards and other stock-based awards. The number of shares initially reserved for issuance under the 2015 Plan was 2,784,395 shares of common stock. 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. On October 6, 2015, in conjunction with the pricing of the IPO, the Company issued 89,800 stock options.

Stock Option Valuation

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

	Nine Months Ended September 30, 2015		Nine Months Ended September 30, 2014
Risk-free interest rate	1.73	%	1.85	%
Expected term (in years)	6.22		6.18
Expected volatility	96.65	%	116.05	%
Expected dividend yield	0	%	0	%

The Company recognizes compensation expense for only the portion of awards that are expected to vest. For the three and nine months ended September 30, 2015 and 2014, the Company applied an expected forfeiture rate of 0%.

Stock Options

The following table summarizes stock option activity under the 2012 Plan from January 1, 2015 through September 30, 2015:

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
					(in years)
Outstanding as of December 31, 2014	500,262		$	1.22	9.77	$	305
Granted	640,262		$	10.66
Exercised	—		—
Forfeited and canceled	—		—

Outstanding as of September 30, 2015	1,140,524		$	6.79	9.53	$	5,110

Options vested and expected to vest as of September 30, 2015	1,140,524		$	6.79	9.53	$	5,110

Options exercisable as of September 30, 2015	130,075	(1)	$	0.67	8.78	$	1,343

(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 September 30, 2015.

The weighted average grant-date fair value of stock options granted during the nine months ended September 30, 2015 was $8.34 per share.

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.

Stock-Based Compensation

For the three and nine months ended September 30, 2015 and 2014, the Company recorded stock-based compensation in the following expense categories of its statements of operations and comprehensive loss:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014

Research and development	$	47	$	2	$	74	$	4
General and administrative	111		4		169		4

	$	158	$	6	$	243	$	8

As of September 30, 2015, the Company had an aggregate of $5,906 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 3.53 years.

- Definition

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

+ References+ Details

Net Loss per Share

9 Months Ended

Sep. 30, 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:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014

Numerator:
Net loss	$	(10,633	)	$	(2,657	)	$	(15,849	)	$	(5,920	)
Accretion of convertible preferred stock to redemption value	(995		)	(479		)	(2,353		)	(1,394		)

Net loss attributable to common stockholders	$	(11,628	)	$	(3,136	)	$	(18,202		$	(7,314	)

Denominator:
Weighted average shares of common stock outstanding	2,730,427			2,730,427			2,730,427			2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding	(455,810		)	(935,518		)	(574,742		)	(1,054,451		)

Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted	2,274,617			1,794,909			2,155,685			1,675,976

Net loss per share attributable to common stockholders, basic and diluted	$	(5.11	)	$	(1.75	)	$	(8.44	)	$	(4.36	)

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 September 30, 2015.

The Company’s potential dilutive securities, which include stock options, unvested restricted common stock and 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 both the three and nine months ended September 30, 2015 and 2014 because including them would have had an anti-dilutive effect:

	2015	2014

Stock options to purchase common stock	1,140,524	168,110
Unvested restricted common stock	399,757	879,466
Convertible preferred stock (as converted to common stock)	11,677,076	7,924,919

	13,217,357	8,972,495

- Definition

The entire disclosure for earnings per share.

+ References+ Details

Commitments and Contingencies

9 Months Ended

Sep. 30, 2015

Commitments and Contingencies

Commitments and Contingencies

10. Commitments and Contingencies

Lease

In September 2013, the Company entered into a sublease agreement for its office space with related parties (see Note 11), with a term ending on November 30, 2016. As part of an amendment to the sublease agreement entered into in December 2014, the Company increased the amount of office space to be leased and agreed to new monthly lease 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 lease to November 2019. Rent expense under operating leases was $34 and $17 for the three months ended September 30, 2015 and 2014, respectively, and $86 and $50 for the nine months

ended September 30, 2015 and 2014, respectively. The Company recognizes rent expense on a straight-line basis over the lease period and has accrued for rent expense incurred but not yet paid.

As of September 30, 2015, future minimum lease payments under the sublease were as follows:

Years Ending December 31,
2015	$	42
2016	193
2017	198
2018	202
2019	189

Total	$	824

- Definition

The entire disclosure for commitments and contingencies.

+ References+ Details

Related Party Transactions	9 Months Ended
Related Party Transactions	Sep. 30, 2015
Related Party Transactions
Related Party Transactions	11. Related Party Transactions In September 2013, the Company entered into a direct sublease agreement with NeXeption, Inc. (“NeXeption”) for its leased space (see Note 10). A member of the Company’s board of directors is a current executive officer of NeXeption. Total payments made during the three months ended September 30, 2015 and 2014 and the nine months ended September 30, 2015 and 2014 under these sublease agreements were $34, $17, $86 and $50, 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 three months ended September 30, 2015 and 2014 and nine months ended September 30, 2015 and 2014, gross expenses incurred by the Company under the services agreement totaled $105, $119, $358 and $358, respectively, and gross expenses charged to NST by the Company totaled $132, $103, $376 and $310, respectively. For the three months ended September 30, 2015 and 2014 and nine months ended September 30, 2015 and 2014, the Company recorded $36, $79, $172 and $238, respectively, of general and administrative expenses and $63, $63, $190 and $190, respectively, as a reduction of research and development expenses related to these transactions. During the three months ended September 30, 2015 and 2014 and nine months ended September 30, 2015 and 2014, payments made to NST by the Company totaled $0, $5, $16 and $37, respectively. Related to this agreement, no amounts were due to or due from NST at September 30, 2015.

- 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

License Agreement with Rigel Pharmaceuticals, Inc.	9 Months Ended
License Agreement with Rigel Pharmaceuticals, Inc.	Sep. 30, 2015
License Agreement with Rigel Pharmaceuticals, Inc.
License Agreement with Rigel Pharmaceuticals, Inc.	12. 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 three months ended September 30, 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 three months ended September 30, 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.

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2015
Income Taxes
Income Taxes	13. Income Taxes The Company did not record a federal or state income tax benefit for the Company’s losses for the three and nine months ended September 30, 2015 and 2014 due to the Company’s conclusion that a valuation allowance is required.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References+ Details

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2015
Subsequent Events
Subsequent Events	14. Subsequent Events On October 6, 2015, in connection with the IPO, the Company’s Registration Statement on Form S-1 was declared effective by the SEC, and on October 7, 2015, the Company’s Common Stock began trading on the NASDAQ Global Select Market under the symbol ACRS. On October 13, 2015, immediately prior to the closing of the IPO, all outstanding shares of Preferred Stock automatically converted into shares of Common Stock at the applicable conversion ratio then in effect. As a result of the conversion, as of October 13, 2015, the Company had no shares of Preferred Stock outstanding. On October 13, 2015, the Company closed the IPO. The Company received net proceeds of $56,623 from the IPO, net of underwriting discounts and commissions and other estimated offering expenses (see Note 1). On October 13, 2015, the Board granted 89,800 options with an exercise price of $11.00 per share pursuant to the 2015 Plan. The awards vest over periods of between three and four years and expire after ten years (see Note 8). On October 13, 2015, in connection with the IPO, the Company amended and restated its certificate of incorporation to reflect the following authorized share increases: 110,000,000 shares of capital stock, consisting of 100,000,000 shares of common stock, par value $0.00001 per share and 10,000,000 shares of preferred stock, par value $0.00001 per share.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2015
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The accompanying condensed 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, Aclaris Therapeutics International Limited. All intercompany transactions have been eliminated.
Use of Estimates	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, the accrual of research and development expenses and the valuation of common stock and 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.
Deferred Offering costs	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’ deficit as a reduction of additional paid-in capital generated as a result of the offering. As of September 30, 2015, the Company had recorded $1,943 of deferred offering costs incurred in connection with the IPO. The deferred offering costs were offset against the net proceeds received upon completion of the IPO in October 2015.

Fair Value of Financial Assets and Liabilities (Tables)

9 Months Ended

Sep. 30, 2015

Fair Value of Financial Assets and Liabilities

Schedule of 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 September 30, 2015 Using:
	Level 1		Level 2		Level 3		Total

Assets:
Cash equivalents	$	25,020	$	—	$	—	$	25,020
Marketable securities	—		12,986		—		12,986

	$	25,020	$	12,986	$	—	$	38,006

	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 the Company's available for sale marketable securities by type of security

	September 30, 2015
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
Marketable securities:
Corporate debt securities	$	12,985	$	1	$	—	$	12,986

	$	12,985	$	1	$	—	$	12,986

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

	$	5,897	$	—	$	(6	)	$	5,891

Property and Equipment, Net (Tables)

9 Months Ended

Sep. 30, 2015

Property and Equipment, Net

Schedule of property and equipment, net

	September 30, 2015			December 31, 2014
Computer equipment	$	190		$	36
Manufacturing equipment	578			—
Construction in progress	77			506

	845			542
Less: Accumulated depreciation	(84		)	(27		)

	$	761		$	515

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2015

Accrued Expenses

Schedule of accrued expenses

	September 30, 2015		December 31, 2014
Payroll and payroll-related costs	$	463	$	—
Clinical trial expenses	284		163
Deferred offering costs	178		—
Other	14		25

	$	939	$	188

Convertible Preferred Stock (Tables)

9 Months Ended

Sep. 30, 2015

Convertible Preferred Stock.

Schedule of redeemable preferred stock

	September 30, 2015
	Preferred Shares Authorized	Preferred Shares Issued and Outstanding	Carrying Value		Liquidation Preference		Common Stock Issuable Upon Conversion
Series A convertible preferred stock	20,890,000	20,890,000	$	26,178	$	26,491	6,055,060
Series B convertible preferred stock	6,451,057	6,451,057	12,263		11,496		1,869,859
Series C convertible preferred stock	12,944,984	12,944,984	39,864		40,295		3,752,157

	40,286,041	40,286,041	$	78,305	$	78,282	11,677,076

	December 31, 2014
	Preferred Shares Authorized	Preferred Shares Issued and Outstanding	Carrying Value		Liquidation Preference		Common Stock Issuable Upon Conversion
Series A convertible preferred stock	20,890,000	20,890,000	$	24,879	$	25,023	6,055,060
Series B 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

- Definition

Tabular disclosure of temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

+ References+ Details

Stockholders' Deficit (Tables)

9 Months Ended

Sep. 30, 2015

Stockholders' Deficit

Summary of restricted stock activity

	Number of Shares	Weighted Average Grant Date Fair Value Per Share
Unvested restricted common stock as of December 31, 2014	759,538	$	0.00001
Vested	359,781	$	0.00001

Unvested restricted common stock as of September 30, 2015	399,757	$	0.00001

Stock-Based Awards (Tables)

9 Months Ended

Sep. 30, 2015

Stock-Based Awards

Assumptions used to determine fair value of stock options granted

	Nine Months Ended September 30, 2015		Nine Months Ended September 30, 2014
Risk-free interest rate	1.73	%	1.85	%
Expected term (in years)	6.22		6.18
Expected volatility	96.65	%	116.05	%
Expected dividend yield	0	%	0	%

Summary of stock option activity

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
					(in years)
Outstanding as of December 31, 2014	500,262		$	1.22	9.77	$	305
Granted	640,262		$	10.66
Exercised	—		—
Forfeited and canceled	—		—

Outstanding as of September 30, 2015	1,140,524		$	6.79	9.53	$	5,110

Options vested and expected to vest as of September 30, 2015	1,140,524		$	6.79	9.53	$	5,110

Options exercisable as of September 30, 2015	130,075	(1)	$	0.67	8.78	$	1,343

(1)

Stock-based compensation expense

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014

Research and development	$	47	$	2	$	74	$	4
General and administrative	111		4		169		4

	$	158	$	6	$	243	$	8

Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2015

Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders

	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014

Numerator:
Net loss	$	(10,633	)	$	(2,657	)	$	(15,849	)	$	(5,920	)
Accretion of convertible preferred stock to redemption value	(995		)	(479		)	(2,353		)	(1,394		)

Net loss attributable to common stockholders	$	(11,628	)	$	(3,136	)	$	(18,202		$	(7,314	)

Denominator:
Weighted average shares of common stock outstanding	2,730,427			2,730,427			2,730,427			2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding	(455,810		)	(935,518		)	(574,742		)	(1,054,451		)

Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted	2,274,617			1,794,909			2,155,685			1,675,976

Net loss per share attributable to common stockholders, basic and diluted	$	(5.11	)	$	(1.75	)	$	(8.44	)	$	(4.36	)

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

	2015	2014

Stock options to purchase common stock	1,140,524	168,110
Unvested restricted common stock	399,757	879,466
Convertible preferred stock (as converted to common stock)	11,677,076	7,924,919

	13,217,357	8,972,495

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2015

Commitments and Contingencies

Schedule of future minimum lease payments under the sublease

Years Ending December 31,
2015	$	42
2016	193
2017	198
2018	202
2019	189

Total	$	824

Nature of Business and Basis of Presentation (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended		3 Months Ended		9 Months Ended			0 Months Ended	1 Months Ended	0 Months Ended		0 Months Ended
	Sep. 30, 2015	Sep. 24, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Oct. 13, 2015 Subsequent event	Oct. 31, 2015 Subsequent event	Oct. 13, 2015 Subsequent event IPO	Oct. 13, 2015 Subsequent event IPO	Oct. 13, 2015 Subsequent event Exercise of over-allotment option	Oct. 13, 2015 Subsequent event Exercise of over-allotment option
Initial public offering
Number of shares issued in offering										5,000,000		750,000
Issuance price (in dollars per share)											$ 11.00		$ 11.00
Gross proceeds from initial public offering										$ 55,000		$ 8,250
Common stock shares issued upon conversion of convertible preferred stock								11,677,076	11,677,076
Payments for underwriting discounts and commissions								4,428
Offering costs incurred								2,200
Net offering proceeds								56,623
Reverse stock split		0.2899
Working capital			37,463		37,463
Accumulated deficit			38,119		38,119		20,749
Cash, cash equivalents and marketable securities			38,405		38,405
Offering proceeds, net of underwriting discounts and commissions								58,823
Product revenues			$ 0	$ 0	$ 0	$ 0
Minimum period following balance sheet that the cash and cash equivalents of the entity are expected to be sufficient to fund operations (in months)	24 months

Fair Value of Financial Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Assets:
Marketable securities	$ 12,986	$ 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	25,020	10,012
Marketable securities	12,986	5,891
Total assets measured at fair value	38,006	15,903
Recurring \| Level 1
Assets:
Cash equivalents	25,020	10,012
Total assets measured at fair value	25,020	10,012
Recurring \| Level 2
Assets:
Marketable securities	12,986	5,891
Total assets measured at fair value	$ 12,986	$ 5,891

Fair Value of Financial Assets and Liabilities (Details 2) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Marketable securities:
Amortized Cost	$ 12,985	$ 5,897
Gross Unrealized Gain	1
Gross Unrealized Loss		(6)
Fair Value	12,986	5,891
Corporate debt securities
Marketable securities:
Amortized Cost	12,985	5,096
Gross Unrealized Gain	1
Gross Unrealized Loss		(6)
Fair Value	12,986	5,090
Corporate debt securities \| Maximum
Marketable securities:
Remaining term of maturities (in months)	8 months	13 months
U.S. government agencies debt securities
Marketable securities:
Amortized Cost		801
Fair Value		$ 801

Property and Equipment, Net (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Property and Equipment, net
Property and equipment	$ 845		$ 845		$ 542
Less: accumulated depreciation	(84)		(84)		(27)
Property and equipment, net	761		761		515
Depreciation	32	3	57	9
Computer equipment
Property and Equipment, net
Property and equipment	190		190		36
Manufacturing equipment
Property and Equipment, net
Property and equipment	578		578
Construction in progress
Property and Equipment, net
Property and equipment	$ 77		$ 77		$ 506

Accrued Expenses (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015	Dec. 31, 2014
Accrued Expenses
Payroll and payroll-related costs	$ 463
Clinical trial expenses	284	163
Deferred offering costs	178
Other	14	25
Accrued expenses, total	$ 939	$ 188

- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable arising from transactions not otherwise specified in the taxonomy. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References+ Details

Convertible Preferred Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended		0 Months Ended	1 Months Ended		9 Months Ended	12 Months Ended	1 Months Ended	9 Months Ended	12 Months Ended	1 Months Ended	0 Months Ended	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Oct. 13, 2015 Subsequent event	Oct. 31, 2015 Subsequent event	Oct. 13, 2015 Subsequent event	Sep. 30, 2015 Series A convertible preferred stock	Dec. 31, 2014 Series A convertible preferred stock	Sep. 30, 2014 Series B convertible preferred stock	Sep. 30, 2015 Series B convertible preferred stock	Dec. 31, 2014 Series B convertible preferred stock	Sep. 30, 2014 Series B convertible preferred stock Put option Long position Milestone director	Aug. 28, 2015 Series C convertible preferred stock	Sep. 30, 2015 Series C convertible preferred stock	Aug. 28, 2015 Series C convertible preferred stock
Convertible Preferred Stock
Authorized (in shares)	40,286,041	34,090,000				20,890,000	20,890,000		6,451,057	13,200,000			12,944,984
Par value (in dollars per share)	$ 0.00001	$ 0.00001
New issues (in shares)	12,944,984							6,451,057				12,944,984
Issue price of shares (in dollars per share)								$ 1.65						$ 3.09
Proceeds from issuance								$ 10,644				$ 40,000
Number of milestones to attain for call of purchased put option											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)											$ 1.65
Number of directors for confirming exercise of option											5
Percentage of voting stockholders for confirming exercise of option											60.00%
Issuance costs of temporary equity	136							60
Fair value of purchased put option											1,039
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											$ 0
Fair value of underlying instruments (as a percent)											$ 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%
Preferred shares issued (in shares)	40,286,041	27,341,057				20,890,000	20,890,000		6,451,057	6,451,057			12,944,984
Preferred shares outstanding (in shares)	40,286,041	27,341,057			0	20,890,000	20,890,000		6,451,057	6,451,057			12,944,984
Carrying Value	78,305	36,677				26,178	24,879		12,263	11,798			39,864
Liquidation Preference	78,282	35,882				26,491	25,023		11,496	10,859			40,295
Common Stock Issuable Upon Conversion	11,677,076	7,924,919				6,055,060	6,055,060		1,869,859	1,869,859			3,752,157
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)	$ 12.80
Minimum percentage of holders required for determination of conversion date	60.00%
Conversion price (in dollars per share)						$ 3.45			$ 5.6925				$ 10.6605
Conversion ratio						3.45	3.45		3.45	3.45
Common stock shares issued upon conversion of convertible preferred stock			11,677,076	11,677,076

Stockholders' Deficit (Details) (USD $)	9 Months Ended
Stockholders' Deficit (Details) (USD $)	Sep. 30, 2015 Vote	Dec. 31, 2014
Stockholders' Deficit
Common stock shares authorized	110,000,000	77,000,000
Common stock par value (in dollars per share)	$ 0.00001	$ 0.00001
Number of votes per share	1
Dividends declared	$ 0
Common stock shares reserved	13,216,245	8,425,181

Stockholders' Deficit (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2012	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Stock-based awards
Number of shares of stock issued to founders, including restricted stock	2,730,427
Number of shares of restricted stock issued	1,918,834
Estimated grant-date fair value (in dollars per share)	$ 0.00001
Number of restricted stock shares subject to repurchase		399,757		399,757		759,538
Number of Shares
Number of shares, beginning balance				759,538
Number of shares, Vested				359,781
Number of shares, ending balance		399,757		399,757
Weighted Average Grant Date Fair Value Per Share
Weighted average grant date fair value, beginning balance (in dollars per share)				$ 0.00001
Weighted average grant date fair value, vested (in dollars per share)				$ 0.00001
Weighted average grant date fair value, ending balance (in dollars per share)		$ 0.00001		$ 0.00001
Aggregate intrinsic value of awards that vested during the period		$ 1,091	$ 170	$ 2,026	$ 269
Unvested 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
Unvested 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 $) In Thousands, except Share data, unless otherwise specified	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended		9 Months Ended	0 Months Ended
	Sep. 30, 2015	Sep. 30, 2015 Employee, director and consultant stock options	Sep. 30, 2014 Employee, director and consultant stock options	Sep. 30, 2015 Employee, director and consultant stock options	Sep. 30, 2014 Employee, director and consultant stock options	Dec. 31, 2014 2012 Equity Compensation Plan	Sep. 30, 2015 2012 Equity Compensation Plan	Aug. 25, 2015 2012 Equity Compensation Plan	Sep. 30, 2015 2012 Equity Compensation Plan Maximum	Oct. 06, 2015 2015 Equity Incentive Plan	Sep. 15, 2015 2015 Equity Incentive Plan
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
Number of shares authorized						500,262		1,539,169			2,784,395
Number of shares available for grant						0	398,645
Percentage increase to shares available for grant from common outstanding as of preceding December 31 (as a percent)											4.00%
Options granted (in shares)							640,262			89,800
Stock Option Valuation
Risk-free interest rate (as a percent)				1.73%	1.85%
Expected term (in years)				6 years 2 months 19 days	6 years 2 months 5 days
Expected volatility (as a percent)				96.65%	116.05%
Expected dividend yield (as a percent)				0.00%	0.00%
Expected forfeiture rate (as a percent)		0.00%	0.00%	0.00%	0.00%
Number of Shares
Number of Shares, beginning balance							500,262
Number of Shares, Granted							640,262			89,800
Number of Shares, ending balance						500,262	1,140,524
Number of Shares, Options vested and expected to vest							1,140,524
Number of Shares, Options exercisable							130,075
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)							$ 10.66
Weighted Average Exercise Price, ending balance (in dollars per share)						$ 1.22	$ 6.79
Weighted Average Exercise Price, Options vested and expected to vest (in dollars per share)							$ 6.79
Weighted Average Exercise Price, Options exercisable (in dollars per share)							$ 0.67
Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term (in years)						9 years 9 months 7 days	9 years 6 months 11 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest (in years)							9 years 6 months 11 days
Weighted Average Remaining Contractual Term, Options exercisable (in years)							8 years 9 months 11 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value						$ 305	$ 5,110
Aggregate Intrinsic Value, Options vested and expected to vest							5,110
Aggregate Intrinsic Value, Options exercisable							$ 1,343
Weighted average grant-date fair value of stock options granted (in dollars per share)	$ 8.34

Stock-Based Awards (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Stock-based compensation expense
Stock-based compensation expense	$ 158	$ 6	$ 243	$ 8
Unrecognized stock-based compensation cost	5,906		5,906
Weighted average period unrecognized stock-based compensation cost to be recognized (in years)			3 years 6 months 11 days
Research and development expense.
Stock-based compensation expense
Stock-based compensation expense	47	2	74	4
General and administrative expense.
Stock-based compensation expense
Stock-based compensation expense	$ 111	$ 4	$ 169	$ 4

Net Loss per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net loss	$ (10,633)	$ (2,657)	$ (15,849)	$ (5,920)
Accretion of convertible preferred stock to redemption value	(995)	(479)	(2,353)	(1,394)
Net loss attributable to common stockholders	$ (11,628)	$ (3,136)	$ (18,202)	$ (7,314)
Denominator:
Weighted average shares of common stock outstanding (in shares)	2,730,427	2,730,427	2,730,427	2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding (in shares)	(455,810)	(935,518)	(574,742)	(1,054,451)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted (in shares)	2,274,617	1,794,909	2,155,685	1,675,976
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (5.11)	$ (1.75)	$ (8.44)	$ (4.36)

- Definition

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

+ References+ Details

- Definition

This element represents the weighted average total number of shares issued throughout the period including the first (beginning balance outstanding) and last (ending balance outstanding) day of the period before considering any reductions (for instance, shares held in treasury) to arrive at the weighted average number of shares outstanding. Weighted average relates to the portion of time within a reporting period that common shares have been issued and outstanding to the total time in that period. Such concept is used in determining the weighted average number of shares outstanding for purposes of calculating earnings per share (basic).

+ References+ Details

Net Loss per Share (Details 2)	3 Months Ended		9 Months Ended
Net Loss per Share (Details 2)	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	13,217,357	8,972,495	13,217,357	8,972,495
Employee, director and consultant stock options
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	1,140,524	168,110	1,140,524	168,110
Unvested restricted common stock
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	399,757	879,466	399,757	879,466
Convertible preferred stock
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	11,677,076	7,924,919	11,677,076	7,924,919

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References+ Details

Commitments and Contingencies (Details) (Director, Direct sublease agreement, USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Director \| Direct sublease agreement
Lease
Expenses incurred under related party transactions	$ 34	$ 17	$ 86	$ 50
Future minimum lease payments under the sublease
2015	42		42
2016	193		193
2017	198		198
2018	202		202
2019	189		189
Total	$ 824		$ 824

Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Director \| Direct sublease agreement
Related Party Transactions
Payments made for related party transactions	$ 34	$ 17	$ 86	$ 50
Expenses incurred under related party transactions	34	17	86	50
Certain officers \| Services agreement
Related Party Transactions
Payments made for related party transactions	0	5	16	37
Expenses incurred under related party transactions	105	119	358	358
Other revenue earned from related party transactions	132	103	376	310
Amounts due to or from related party	0		0
Certain officers \| Services agreement \| General and administrative expense.
Related Party Transactions
Net expenses (revenues) from related party transactions	36	79	172	238
Certain officers \| Services agreement \| Research and development expense.
Related Party Transactions
Net expenses (revenues) from related party transactions	$ (63)	$ (63)	$ (190)	$ (190)

License Agreement with Rigel Pharmaceuticals, Inc. (Details) (License and collaboration agreement, Rigel, JAK inhibitors, USD $) In Thousands, unless otherwise specified	0 Months Ended	3 Months Ended
	Aug. 27, 2015	Sep. 30, 2015	Aug. 27, 2015
License Agreement
Upfront non-refundable payment		$ 8,000
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
Period from first commercial product sale that royalties are owed (in years)	10 years
Research and development expense.
License Agreement
Upfront payment recognized as expense		$ 8,000

Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Taxes
Federal income tax benefit	$ 0	$ 0	$ 0	$ 0
State income tax benefit	$ 0	$ 0	$ 0	$ 0

Subsequent Events (Details) (USD $) In Thousands, except Share data, unless otherwise specified			0 Months Ended			0 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Oct. 06, 2015 2015 Equity Incentive Plan	Oct. 13, 2015 Subsequent event	Oct. 13, 2015 Subsequent event	Oct. 13, 2015 Subsequent event 2015 Equity Incentive Plan	Oct. 13, 2015 Subsequent event 2015 Equity Incentive Plan Employee, director and consultant stock options	Oct. 13, 2015 Subsequent event 2015 Equity Incentive Plan Employee, director and consultant stock options Minimum	Oct. 13, 2015 Subsequent event 2015 Equity Incentive Plan Employee, director and consultant stock options Maximum
Subsequent events
Preferred shares outstanding (in shares)	40,286,041	27,341,057			0
Net offering proceeds				$ 56,623
Options granted (in shares)			89,800			89,800
Exercise price of options granted (in dollars per share)						$ 11.00
Vesting period (in years)								3 years	4 years
Term of award (in years)							10 years
Number of additional shares of capital stock authorized				110,000,000
Number of additional shares of common stock authorized				100,000,000
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001			$ 0.00001
Number of additional shares of preferred stock authorized				10,000,000
Preferred stock, par value (in dollars per share)					$ 0.00001

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT (Parenthetical) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2015
Condensed Consolidated Statements Of Convertible Preferred Stock and Stockholders' Deficit (Unaudited)
Issuance of Series C convertible preferred stock, issuance costs	$ 136

Organization and Nature of Business (Details) (A-101)	Sep. 30, 2015 item
A-101
Production information
Number of clinical trials completed	3

Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015
Deferred offering costs
Deferred offering costs	$ 1,943