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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2013	Jul. 31, 2013
Document and Entity Information
Entity Registrant Name	Verastem, Inc.
Entity Central Index Key	0001526119
Document Type	10-Q
Document Period End Date	Jun. 30, 2013
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		25,593,992
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q2

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 13,880	$ 10,096
Short-term investments	43,571	46,480
Prepaid expenses and other current assets	841	506
Total current assets	58,292	57,082
Property and equipment, net	730	811
Long-term investments	20,558	34,944
Restricted cash	86	86
Other long-term assets	295
Total assets	79,961	92,923
Current liabilities:
Accounts payable	2,034	1,848
Accrued expenses	2,354	551
Other current liabilities	850
Total current liabilities	5,238	2,399
Deferred rent	16	38
Liability for shares subject to repurchase	16	20
Stockholders' equity
Preferred stock, $0.0001 par value; 5,000 shares authorized; none issued
Common stock, $0.0001 par value; 100,000, shares authorized 20,794 and 20,364 shares issued and outstanding at June 30, 2013 and December 31, 2012, respectively	2	2
Additional paid-in capital	140,430	136,893
Accumulated other comprehensive (loss) income	(3)	22
Deficit accumulated during the development stage	(65,738)	(46,451)
Total stockholders' equity	74,691	90,466
Total liabilities, redeemable convertible preferred stock and stockholders' equity	$ 79,961	$ 92,923

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares shares in Thousands	Jun. 30, 2013	Dec. 31, 2012
CONDENSED CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000	5,000
Preferred stock, shares issued	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000	100,000
Common stock, shares issued	20,794	20,364
Common stock, shares outstanding	20,794	20,364

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		35 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
Operating expenses:
Research and development	$ 6,045	$ 4,683	$ 11,341	$ 9,486	$ 43,336
General and administrative	4,239	2,213	8,024	4,338	22,741
Total operating expenses	10,284	6,896	19,365	13,824	66,077
Loss from operations	(10,284)	(6,896)	(19,365)	(13,824)	(66,077)
Interest income	34	71	78	128	339
Net loss	(10,250)	(6,825)	(19,287)	(13,696)	(65,738)
Accretion of preferred stock				(6)	(40)
Net loss applicable to common stockholders	$ (10,250)	$ (6,825)	$ (19,287)	$ (13,702)	$ (65,778)
Net loss per share applicable to common stockholders-basic and diluted (in dollars per share)	$ (0.49)	$ (0.34)	$ (0.94)	$ (0.79)	$ (6.20)
Weighted-average number of common shares used in net loss per share applicable to common stockholders-basic and diluted (in shares)	20,729	19,863	20,607	17,278	10,608
Comprehensive loss	$ (10,271)	$ (6,791)	$ (19,312)	$ (13,705)	$ (65,741)

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended		35 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
Operating activities
Net loss	$ (19,287)	$ (13,696)	$ (65,738)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	112	94	402
Stock-based compensation expense	5,182	3,012	14,269
Common stock issued in exchange for license			2,003
Obligation to issue a warrant in exchange for license			439
Change in fair value of obligation to issue warrant		431	398
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(630)	(379)	(1,136)
Accounts payable	186	177	2,034
Accrued expenses and deferred rent	1,781	420	2,370
Net cash used in operating activities	(12,656)	(9,941)	(44,959)
Investing activities
Purchases of property and equipment	(31)	(167)	(1,134)
Purchases of investments	(44,209)	(116,923)	(234,088)
Maturities of investments	61,479	64,229	169,958
Increase in restricted cash			(86)
Net cash provided by (used in) investing activities	17,239	(52,861)	(65,350)
Financing activities
Proceeds from issuance of redeemable convertible preferred stock			68,107
Proceeds from the exercise of stock options	30		33
Net proceeds from the issuance of common stock and restricted common stock		57,599	56,878
Cash used to settle restricted stock liability awards	(829)		(829)
Net cash (used in) provided by financing activities	(799)	57,599	124,189
Increase (decrease) in cash and cash equivalents	3,784	(5,203)	13,880
Cash and cash equivalents at beginning of period	10,096	20,954
Cash and cash equivalents at end of period	$ 13,880	15,751	13,880
Supplemental disclosure of non-cash financing activity
Accretion of redeemable convertible preferred stock to redemption value		6	40
Conversion of redeemable convertible preferred stock upon initial public offering		68,148	68,148
Reclassification of obligation to issue warrant from liabilities to equity		$ 837	$ 837

Summary of significant accounting policies	6 Months Ended
Summary of significant accounting policies	Jun. 30, 2013
Summary of significant accounting policies
Summary of significant accounting policies	1. Summary of significant accounting policies Basis of presentation The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States ("GAAP") for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (including those which are normal and recurring) considered necessary for a fair presentation of the interim financial information have been included. When preparing financial statements in conformity with GAAP, the Company must make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses and related disclosures at the date of the financial statements. Actual results could differ from those estimates. Additionally, operating results for the three months ended June 30, 2013 are not necessarily indicative of the results that may be expected for any other interim period or for the fiscal year ending December 31, 2013. For further information, refer to the financial statements and footnotes included in the Company's Annual Report on Form 10-K for the year ended December 31, 2012 as filed with the Securities and Exchange Commission ("SEC") on March 26, 2013. Subsequent Events In preparing the financial statements included in this Form 10-Q, the Company has evaluated all subsequent events that occurred after June 30, 2013 through the date of the filing of this Form 10-Q. In July 2013, the Company closed a public offering in which it sold 4,255,000 shares of its common stock at a price of $15 per share (Note 7).

Fair value of financial instruments

6 Months Ended

Jun. 30, 2013

Fair value of financial instruments

Fair value of financial instruments

2. Fair value of financial instruments

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. The fair value hierarchy is now established that prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs:


Level 1 inputs		Quoted prices in active markets for identical assets or liabilities
Level 2 inputs		Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly
Level 3 inputs		Unobservable inputs that reflect the Company's own assumptions about the assumptions market participants would use in pricing the asset or liability

The following table presents information about the Company's financial assets and liabilities that have been measured at fair value at June 30, 2013 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands).

Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)

Financial assets
Cash equivalents	$	12,208	$	6,208	$	6,000	$	—
Short-term investments		43,571		—		43,571		—
Long-term investments		20,558		—		20,558		—

Total financial assets	$	76,337	$	6,208	$	70,129	$	—

Financial liabilities
Liability classified stock-based compensation awards	$	850	$	—	$	850	$	—

Total financial liabilities	$	850	$	—	$	850	$	—

The following table presents information about the Company's financial assets that have been measured at fair value at December 31, 2012 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands).

Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)

Financial assets
Cash equivalents	$	8,171	$	8,171	$	—	$	—
Short-term investments		46,480		—		46,480		—
Long-term investments		34,944		—		34,944		—

Total financial assets	$	89,595	$	8,171	$	81,424	$	—

The Company's cash equivalents and investments are comprised of money market accounts, government-sponsored enterprise securities and commercial paper of publicly traded companies secured by the U.S. government. These investments have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. These observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events. The Company validates the prices provided by third party pricing services by reviewing their pricing methods and matrices, obtaining market values from other pricing sources, analyzing pricing data in certain instances and confirming that the relevant markets are active. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of June 30, 2013.

The Company's liability classified stock-based compensation awards are comprised of restricted stock units that allow for greater than minimum statutory tax withholdings. These awards are valued based on the fair value of the Company's common stock underlying the awards, which is traded on an active market.

- 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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Reference 9: http://www.xbrl.org/2003/role/presentationRef
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Investments

6 Months Ended

Jun. 30, 2013

Investments

Investments

3. Investments

The Company's investments are classified as available-for-sale pursuant to Accounting Standards Codification (ASC) 320, Investments—Debt and Equity Securities. The Company classifies investments available to fund current operations as current assets on its balance sheets. Investments are classified as long-term assets on the balance sheets if (i) the Company has the intent and ability to hold the investments for a period of at least one year and (ii) the contractual maturity date of the investments is greater than one year.

Investments are carried at fair value with unrealized gains and losses included as a component of accumulated other comprehensive (loss) income, until such gains and losses are realized. If a decline in the fair value is considered other-than-temporary, based on available evidence, the unrealized loss is transferred from other comprehensive loss to the statement of operations. There were no charges taken for other-than-temporary declines in fair value of short-term or long-term investments during the three and six months ended June 30, 2013 and 2012 or for the period from August 4, 2010 (inception) to June 30, 2013. The Company recorded ($25,000), ($9,000), ($21,000), $34,000 and ($3,000) of unrealized gains/(losses) during the six months ended June 30, 2013 and 2012, three months ended June 30, 2013 and 2012, and the period from August 4, 2010 (inception) to June 30, 2013, respectively. Realized gains and losses are included in interest income in the statement of operations. There were no realized gains or losses recognized during the three and six months ended June 30, 2013 or 2012 or for the period from August 4, 2010 (inception) to June 30, 2013. The Company utilizes the specific identification method as a basis to determine the cost of securities sold.

The Company reviews investments for other-than-temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment's carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other-than-temporary, the Company considers the intent to sell, or whether it is more likely than not that the Company will be required to sell, the investment before recovery of the investment's amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company's investment policy, the severity and the duration of the impairment and changes in value subsequent to year end. As of June 30, 2013, there were no investments with a fair value that was significantly lower than the amortized cost basis or any investments that had been in an unrealized loss position for a significant period.

Cash, cash equivalents and investments at June 30, 2013 and December 31, 2012 consist of the following (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value

June 30, 2013
Cash and cash equivalents:
Cash and money market accounts	$	7,880	$	—	$	—		$	7,880
Government-sponsored enterprise securities		6,000		—		—			6,000

Total cash and cash equivalents	$	13,880	$	—	$	—		$	13,880
Investments:
Government-sponsored enterprise securities (due within 1 year)	$	43,562	$	10	$	(1	)	$	43,571
Government-sponsored enterprise securities (due within 1 - 2 years)		20,570		—		(12	)		20,558

Total investments	$	64,132	$	10	$	(13	)	$	64,129

Total cash, cash equivalents, and investments	$	78,012	$	10	$	(13	)	$	78,009

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value

December 31, 2012
Cash and cash equivalents:
Cash and money market accounts	$	10,096	$	—	$	—		$	10,096

Total cash and cash equivalents	$	10,096	$	—	$	—		$	10,096
Investments:
Government-sponsored enterprise securities (due within 1 year)	$	46,469	$	14	$	(3	)	$	46,480
Government-sponsored enterprise securities (due within 1 - 2 years)		34,931		14		(1	)		34,944

Total investments	$	81,400	$	28	$	(4	)	$	81,424

Total cash, cash equivalents, and investments	$	91,496	$	28	$	(4	)	$	91,520

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Publisher FASB
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+ Details

Accrued expenses

6 Months Ended

Jun. 30, 2013

Accrued expenses

Accrued expenses

4. Accrued expenses

Accrued expenses consist of the following (in thousands):

	June 30, 2013		December 31, 2012

Contract research organizations	$	942	$	69
Compensation and related benefits		670		173
Other		385		54
Professional fees		316		183
Deferred rent		41		36
Consulting		—		36

	$	2,354	$	551

Net loss per share

6 Months Ended

Jun. 30, 2013

Net loss per share

Net loss per share

5. Net loss per share

Basic and diluted net loss per common share is calculated by dividing net loss applicable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. The Company's potentially dilutive shares, which include outstanding stock options, unvested restricted stock and unvested restricted stock units are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive.

The following potentially dilutive securities were excluded from the calculation of diluted net loss per share due to their anti-dilutive effect:

	Three Months ended				Six Months ended

	Three Months ended				Six Months ended				Period from August 4, 2010 (inception) to June 30, 2013
	June 30, 2013		June 30, 2012		June 30, 2013		June 30, 2012		Period from August 4, 2010 (inception) to June 30, 2013
Outstanding stock options		2,263		495		2,263		495		2,263
Unvested restricted stock		538		1,143		538		1,143		538
Unvested restricted stock units		623		598		623		598		623

Stock-based compensation

6 Months Ended

Jun. 30, 2013

Stock-based compensation

Stock-based compensation

6. Stock-based compensation

In December 2011, the Company adopted the 2012 Incentive Plan (the 2012 Plan). The 2012 Plan became effective upon the closing of the Company's IPO in February 2012. The 2012 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based and cash awards. Upon effectiveness, the number of shares of common stock reserved under the 2012 Plan was the sum of 3,428,571 shares plus the number of shares available under the 2010 Equity Incentive Plan (the 2010 Plan). The number of shares reserved under the 2012 Plan is increased by the number of shares of common stock (up to a maximum of 571,242 shares) subject to outstanding awards under the 2010 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased. The 2012 Plan includes an "evergreen provision" that allows for an annual increase in the number of shares of common stock available for issuance under the 2012 Plan. The annual increase will be added on the first day of each year beginning in 2013 and each subsequent anniversary until the expiration of the 2012 Plan, equal to the lowest of 1,285,714 shares of common stock, 4.0% of the number of shares of common stock outstanding and an amount determined by the board of directors. On January 1, 2013, the shares available under the 2012 Plan increased by 844,448 shares of common stock.

Restricted stock

A summary of the Company's nonvested restricted stock as of June 30, 2013 and changes during the six months ended June 30, 2013 is as follows:

			Weighted- average purchase price per share

Nonvested at December 31, 2012	747,000		$	0.027
Vested	(208,860	)		0.022

Nonvested at June 30, 2013	538,140		$	0.029

As of June 30, 2013, there was $4.4 million of total unrecognized stock-based compensation expense related to non-vested restricted stock. The expense is expected to be recognized over a weighted average period of 1.3 years.

A summary of the Company's nonvested restricted stock units (RSUs) as of June 30, 2013 and changes during the six months ended June 30, 2013 is as follows:

			Weighted- average grant date fair value

Outstanding at December 31, 2012	899,204		$	10.70
Settled	(237,718	)		10.50
Canceled	(38,570	)		11.00

Outstanding at June 30, 2013	622,916		$	10.76

As of June 30, 2013, there was $6.5 million of total unrecognized stock-based compensation expense related to non-vested RSUs granted under the 2012 Plan. The expense is expected to be recognized over a weighted-average period of 2.5 years.

During the first quarter of 2013, the Company amended the terms of certain RSUs related to a total of 657,058 shares of common stock to allow for tax withholdings greater than the minimum required statutory withholding amount. As a result of this change in the terms of the awards, the outstanding RSUs are considered to be liability instruments. As a result of this modification, the Company records a liability for the fair value of the awards as of each reporting date with the change in fair value recorded through the statement of operations. The Company will record stock-based compensation expense equal to the greater of the original grant date fair value of the awards or the settlement date fair value. During the three and six months ended June 30, 2013, the Company deposited with tax authorities $55,000 and $829,000, respectively, to settle the tax liability for awards that settled during the respective periods. The liability related to these awards is recorded within other current liabilities on the consolidated balance sheet as of June 30, 2013.

Stock options

A summary of the Company's stock option activity and related information follows:

			Weighted- average price per share			Aggregate intrinsic value

Outstanding at December 31, 2012	1,424,241		$	6.90
Granted	985,500			9.71
Exercised	(71,527	)		0.42
Canceled	(74,884	)		5.88

Outstanding at June 30, 2013	2,263,330		$	8.36	9.2	$	12,486,058

Exercisable at June 30, 2013	508,195		$	7.17	8.8	$	3,408,595

Vested and expected to vest at June 30, 2013(1)	1,956,947		$	8.71	9.3	$	10,113,988

(1): This represents the number of vested options as of June 30, 2013, plus the number of unvested options expected to vest as of June 30, 2013, based on the unvested options at June 30, 2013, adjusted for the estimated forfeiture rate

The fair value of each stock option is estimated on the grant date using the Black-Scholes option-pricing model using the following assumptions:

	Six Months ended June 31,

	2013	2012
Risk-free interest rate	1.0 - 1.3%	0.8 - 2.7%
Dividend yield	—	—
Volatility	75%	69 - 72%
Expected term (years)	6.0	5.3 - 6.1

- 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 50
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6406099&loc=d3e25284-112666

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5444-113901

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph 64, 65, A240
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 93-6
-Paragraph 53
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Subsequent Events	6 Months Ended
Subsequent Events	Jun. 30, 2013
Subsequent Events
Subsequent Events	7. Subsequent Events In July 2013, the Company closed a public offering in which it sold 4,255,000 shares of its common stock to the public at a price of $15 per share, including 555,000 shares issued pursuant to the exercise of the underwriters' option to purchase additional shares. This offering was completed under the shelf registration statement that was filed on Form S-3 and declared effective by the Securities Exchange Commission on February 14, 2013. The net proceeds from this offering were approximately $59.8 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company.

Summary of significant accounting policies (Policies)	6 Months Ended
Summary of significant accounting policies (Policies)	Jun. 30, 2013
Summary of significant accounting policies
Basis of presentation	Basis of presentation The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States ("GAAP") for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (including those which are normal and recurring) considered necessary for a fair presentation of the interim financial information have been included. When preparing financial statements in conformity with GAAP, the Company must make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses and related disclosures at the date of the financial statements. Actual results could differ from those estimates. Additionally, operating results for the three months ended June 30, 2013 are not necessarily indicative of the results that may be expected for any other interim period or for the fiscal year ending December 31, 2013. For further information, refer to the financial statements and footnotes included in the Company's Annual Report on Form 10-K for the year ended December 31, 2012 as filed with the Securities and Exchange Commission ("SEC") on March 26, 2013.
Subsequent Events	Subsequent Events In preparing the financial statements included in this Form 10-Q, the Company has evaluated all subsequent events that occurred after June 30, 2013 through the date of the filing of this Form 10-Q. In July 2013, the Company closed a public offering in which it sold 4,255,000 shares of its common stock at a price of $15 per share (Note 7).

Fair value of financial instruments (Tables)

6 Months Ended

Jun. 30, 2013

Fair value of financial instruments

Schedule of information about financial assets and liabilities measured at fair value

Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)

Financial assets
Cash equivalents	$	12,208	$	6,208	$	6,000	$	—
Short-term investments		43,571		—		43,571		—
Long-term investments		20,558		—		20,558		—

Total financial assets	$	76,337	$	6,208	$	70,129	$	—

Financial liabilities
Liability classified stock-based compensation awards	$	850	$	—	$	850	$	—

Total financial liabilities	$	850	$	—	$	850	$	—

Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)

Financial assets
Cash equivalents	$	8,171	$	8,171	$	—	$	—
Short-term investments		46,480		—		46,480		—
Long-term investments		34,944		—		34,944		—

Total financial assets	$	89,595	$	8,171	$	81,424	$	—

- Definition

Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring and/or nonrecurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).

+ References + Details

Investments (Tables)

6 Months Ended

Jun. 30, 2013

Investments

Schedule of cash, cash equivalents and investments

Cash, cash equivalents and investments at June 30, 2013 and December 31, 2012 consist of the following (in thousands):

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value

June 30, 2013
Cash and cash equivalents:
Cash and money market accounts	$	7,880	$	—	$	—		$	7,880
Government-sponsored enterprise securities		6,000		—		—			6,000

Total cash and cash equivalents	$	13,880	$	—	$	—		$	13,880
Investments:
Government-sponsored enterprise securities (due within 1 year)	$	43,562	$	10	$	(1	)	$	43,571
Government-sponsored enterprise securities (due within 1 - 2 years)		20,570		—		(12	)		20,558

Total investments	$	64,132	$	10	$	(13	)	$	64,129

Total cash, cash equivalents, and investments	$	78,012	$	10	$	(13	)	$	78,009

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value

December 31, 2012
Cash and cash equivalents:
Cash and money market accounts	$	10,096	$	—	$	—		$	10,096

Total cash and cash equivalents	$	10,096	$	—	$	—		$	10,096
Investments:
Government-sponsored enterprise securities (due within 1 year)	$	46,469	$	14	$	(3	)	$	46,480
Government-sponsored enterprise securities (due within 1 - 2 years)		34,931		14		(1	)		34,944

Total investments	$	81,400	$	28	$	(4	)	$	81,424

Total cash, cash equivalents, and investments	$	91,496	$	28	$	(4	)	$	91,520

Accrued expenses (Tables)

6 Months Ended

Jun. 30, 2013

Accrued expenses

Schedule of accrued expenses

Accrued expenses consist of the following (in thousands):

	June 30, 2013		December 31, 2012

Contract research organizations	$	942	$	69
Compensation and related benefits		670		173
Other		385		54
Professional fees		316		183
Deferred rent		41		36
Consulting		—		36

	$	2,354	$	551

Net loss per share (Tables)

6 Months Ended

Jun. 30, 2013

Net loss per share

Schedule of potentially anti-dilutive securities excluded from calculation of diluted net loss per share

	Three Months ended				Six Months ended

	Three Months ended				Six Months ended				Period from August 4, 2010 (inception) to June 30, 2013
	June 30, 2013		June 30, 2012		June 30, 2013		June 30, 2012		Period from August 4, 2010 (inception) to June 30, 2013
Outstanding stock options		2,263		495		2,263		495		2,263
Unvested restricted stock		538		1,143		538		1,143		538
Unvested restricted stock units		623		598		623		598		623

Stock-based compensation (Tables)

6 Months Ended

Jun. 30, 2013

Stock-based compensation

Summary of nonvested restricted stock

			Weighted- average purchase price per share

Nonvested at December 31, 2012	747,000		$	0.027
Vested	(208,860	)		0.022

Nonvested at June 30, 2013	538,140		$	0.029

Summary of nonvested restricted stock units (RSUs)

			Weighted- average grant date fair value

Outstanding at December 31, 2012	899,204		$	10.70
Settled	(237,718	)		10.50
Canceled	(38,570	)		11.00

Outstanding at June 30, 2013	622,916		$	10.76

Summary of stock option activity and related information

			Weighted- average price per share			Aggregate intrinsic value

Outstanding at December 31, 2012	1,424,241		$	6.90
Granted	985,500			9.71
Exercised	(71,527	)		0.42
Canceled	(74,884	)		5.88

Outstanding at June 30, 2013	2,263,330		$	8.36	9.2	$	12,486,058

Exercisable at June 30, 2013	508,195		$	7.17	8.8	$	3,408,595

Vested and expected to vest at June 30, 2013(1)	1,956,947		$	8.71	9.3	$	10,113,988

(1): This represents the number of vested options as of June 30, 2013, plus the number of unvested options expected to vest as of June 30, 2013, based on the unvested options at June 30, 2013, adjusted for the estimated forfeiture rate

Schedule of assumptions used to estimate fair value of each stock option award on grant date

	Six Months ended June 31,

	2013	2012
Risk-free interest rate	1.0 - 1.3%	0.8 - 2.7%
Dividend yield	—	—
Volatility	75%	69 - 72%
Expected term (years)	6.0	5.3 - 6.1

Summary of significant accounting policies (Details) - Subsequent event	1 Months Ended
	Jul. 31, 2013 $ / shares shares
Subsequent events
Number of shares of common stock sold in public offering \| shares	4,255,000
Share price (in dollars per share) \| $ / shares	$ 15

Fair value of financial instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2013	Dec. 31, 2012
Financial assets
Cash equivalents	$ 13,880	$ 10,096
Short-term investments	43,571	46,480
Investments at fair value	64,129	81,424
Total
Financial assets
Cash equivalents	12,208	8,171
Short-term investments	43,571	46,480
Investments at fair value	20,558	34,944
Total financial assets	76,337	89,595
Financial liabilities
Liability classified stock-based compensation awards	850
Total financial liabilities	850
Quoted prices in active markets (Level 1)
Financial assets
Cash equivalents	6,208	8,171
Total financial assets	6,208	8,171
Significant other observable inputs (Level 2)
Financial assets
Cash equivalents	6,000
Short-term investments	43,571	46,480
Investments at fair value	20,558	34,944
Total financial assets	70,129	$ 81,424
Financial liabilities
Liability classified stock-based compensation awards	850
Total financial liabilities	$ 850

Investments (Details) - USD ($)	3 Months Ended		6 Months Ended		35 Months Ended
Investments (Details) - USD ($)	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments
Charges for other-than-temporary declines in fair value of short-term or long-term investments	$ 0	$ 0	$ 0	$ 0	$ 0
Unrealized gains/(losses) on investments	(21,000)	34,000	(25,000)	(9,000)	(3,000)
Realized gains or losses on investments	00	0	0	0	0
Investments that had been in an unrealized loss position for a significant period	0		0		0
Investments
Cash and cash equivalents, Amortized Cost	13,880,000	$ 15,751,000	13,880,000	$ 15,751,000	13,880,000	$ 10,096,000	$ 20,954,000
Cash and cash equivalents, Fair Value	13,880,000		13,880,000		13,880,000	10,096,000
Investments, Amortized Cost
Amortized Cost	64,132,000		64,132,000		64,132,000	81,400,000
Investments, Gross Unrealized Gains
Gross Unrealized Gains	10,000		10,000		10,000	28,000
Investments, Gross Unrealized Losses
Investments, Gross Unrealized Losses	(13,000)		(13,000)		(13,000)	(4,000)
Fair Value
Investments, Fair Value	64,129,000		64,129,000		64,129,000	81,424,000
Total cash, cash equivalents, and investments, Amortized Cost	78,012,000		78,012,000		78,012,000	91,496,000
Total cash, cash equivalents, and investments, Fair Value	78,009,000		78,009,000		78,009,000	91,520,000
Government-sponsored enterprise securities
Investments, Amortized Cost
Due within 1 year	43,562,000		43,562,000		43,562,000	46,469,000
Due within 1 - 2 years	20,570,000		20,570,000		20,570,000	34,931,000
Investments, Gross Unrealized Gains
Due within 1 year	10,000		10,000		10,000	14,000
Due within 1 - 2 years						14,000
Investments, Gross Unrealized Losses
Due within 1 year	(1,000)		(1,000)		(1,000)	(3,000)
Due within 1 - 2 years	(12,000)		(12,000)		(12,000)	(1,000)
Fair Value
Due within 1 year	43,571,000		43,571,000		43,571,000	46,480,000
Due within 1 - 2 years	20,558,000		20,558,000		20,558,000	34,944,000
Cash and money market accounts
Investments
Cash and cash equivalents, Amortized Cost	7,880,000		7,880,000		7,880,000	10,096,000
Cash and cash equivalents, Fair Value	7,880,000		7,880,000		7,880,000	$ 10,096,000
Government-sponsored enterprise securities
Investments
Cash and cash equivalents, Amortized Cost	6,000,000		6,000,000		6,000,000
Cash and cash equivalents, Fair Value	$ 6,000,000		$ 6,000,000		$ 6,000,000

Accrued expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2013	Dec. 31, 2012
Accrued expenses
Contract research organizations	$ 942	$ 69
Compensation and related benefits	670	173
Other	385	54
Professional fees	316	183
Deferred rent	41	36
Consulting		36
Accrued expenses	$ 2,354	$ 551

- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable for professional fees, such as for legal and accounting services received. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References + Details

- Definition

For a classified balance sheet, the cumulative difference as of the balance sheet date between the payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, within one year of the balance sheet date.

+ References + Details

- 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

Net loss per share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended		35 Months Ended
Net loss per share (Details) - shares shares in Thousands	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
Outstanding stock options
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	2,263	495	2,263	495	2,263
Unvested restricted stock
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	538	1,143	538	1,143	538
Unvested restricted stock units
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	623	598	623	598	623

- 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Antidilution
-URI http://asc.fasb.org/extlink&oid=6505113

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Diluted Earnings Per Share
-URI http://asc.fasb.org/extlink&oid=6510752

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Contingent Stock Agreement
-URI http://asc.fasb.org/extlink&oid=6508534

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
-Subparagraph c
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 13, 14
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 07-4
-Paragraph 4
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 171
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Stock-based compensation (Details) - USD ($)		1 Months Ended	3 Months Ended	6 Months Ended	35 Months Ended
Stock-based compensation (Details) - USD ($)	Jan. 02, 2013	Feb. 29, 2012	Jun. 30, 2013	Jun. 30, 2013	Jun. 30, 2013
Additional disclosures
Cash used to settle restricted stock liability awards				$ 829,000	$ 829,000
2012 Plan
Additional disclosures
Initial number of shares reserved		3,428,571
Maximum incremental number of shares reserved		571,242
Annual increase in number of shares reserved				1,285,714
Percentage of outstanding shares of common stock used to compute annual increase in number of shares reserved				4.00%
Increase in number of shares reserved	844,448
Restricted stock
Shares
Outstanding at the beginning of the period (in shares)	747,000			747,000
Vested (in shares)				(208,860)
Outstanding at the end of the period (in shares)			538,140	538,140	538,140
Weighted-average grant date fair value
Outstanding at the beginning of the period (in dollars per share)	$ 0.027			$ 0.027
Vested (in dollars per share)				0.022
Outstanding at the end of the period (in dollars per share)			$ 0.029	$ 0.029	$ 0.029
Additional disclosures
Total unrecognized stock-based compensation expense (in dollars)			$ 4,400,000	$ 4,400,000	$ 4,400,000
Weighted-average recognition period				1 year 3 months 18 days
RSUs
Shares
Outstanding at the beginning of the period (in shares)	899,204		657,058	899,204
Settled (in shares)				(237,718)
Canceled (in shares)				(38,570)
Outstanding at the end of the period (in shares)			622,916	622,916	622,916
Weighted-average grant date fair value
Outstanding at the beginning of the period (in dollars per share)	$ 10.70			$ 10.70
Settled (in dollars per share)				10.50
Canceled (in dollars per share)				11.00
Outstanding at the end of the period (in dollars per share)			$ 10.76	$ 10.76	$ 10.76
Additional disclosures
Total unrecognized stock-based compensation expense (in dollars)			$ 6,500,000	$ 6,500,000	$ 6,500,000
Weighted-average recognition period				2 years 6 months
Cash used to settle restricted stock liability awards			$ 55,000	$ 829,000

Stock-based compensation (Details 2) - Stock options - USD ($)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Shares
Outstanding at the beginning of the period (in shares)	1,424,241
Granted (in shares)	985,500
Exercised (in shares)	(71,527)
Canceled (in shares)	(74,884)
Outstanding at the end of the period (in shares)	2,263,330
Exercisable at the end of the period (in shares)	508,195
Vested and expected to vest at end of period (in shares)	1,956,947
Weighted-average price per share
Outstanding at the beginning of the period (in dollars per share)	$ 6.90
Granted (in dollars per share)	9.71
Exercised (in dollars per share)	0.42
Canceled (in dollars per share)	5.88
Outstanding at the end of the period (in dollars per share)	8.36
Exercisable at the end of the period (in dollars per share)	7.17
Vested and expected to vest at end of the period (in dollars per share)	$ 8.71
Weighted-average remaining contractual term
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	9 years 2 months 12 days
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	9 years 2 months 12 days
Exercisable at the end of the period	8 years 9 months 18 days
Vested and expected to vest at the end of the period	9 years 3 months 18 days
Aggregate intrinsic value
Outstanding at the end of the period (in dollars)	$ 12,486,058
Exercisable at the end of the period (in dollars)	3,408,595
Vested and expected to vest at end of the period (in dollars)	$ 10,113,988
Assumptions used to estimate fair value of each stock-based award on the grant date
Risk-free interest rate, minimum (as a percent)	1.00%	0.80%
Risk-free interest rate, maximum (as a percent)	1.30%	2.70%
Volatility (as a percent)	75.00%
Volatility, minimum (as a percent)		69.00%
Volatility, maximum (as a percent)		72.00%
Expected term	6 years
Minimum
Assumptions used to estimate fair value of each stock-based award on the grant date
Expected term		5 years 3 months 18 days
Maximum
Assumptions used to estimate fair value of each stock-based award on the grant date
Expected term		6 years 1 month 6 days

Subsequent Events (Details) - Subsequent event $ / shares in Units, $ in Millions	1 Months Ended
	Jul. 31, 2013 USD ($) $ / shares shares
Subsequent events
Number of shares of common stock sold in public offering	4,255,000
Share price (in dollars per share) \| $ / shares	$ 15
Shares of common stock issued pursuant to the exercise of the underwriters' option	555,000
Net proceeds from shares of common stock sold in public offering \| $	$ 59.8