Share-Based Compensation

6 Months Ended

Jun. 30, 2012

Share-Based Compensation [Abstract]

Share-Based Compensation

8. Share-Based Compensation

Share-based compensation expense for the three and six months ended June 30, 2012 and 2011, respectively, was recognized in the accompanying Consolidated Statements of Operations and Comprehensive Loss as follows:

	Three Months Ended June 30,				Six Months Ended June 30,				Cumulative from April 20, 2009 (Inception) to
	2012		2011		2012		2011		June 30, 2012
Research and development	$	592	$	172	$	1,032	$	206	$	1,693
General and administrative		576		166		1,082		191		1,818
Total share-based compensation expense	$	1,168	$	338	$	2,114	$	397	$	3,511

The Company did not recognize a tax benefit related to share-based compensation expense during the three and six months ended June 30, 2012 and 2011, respectively, as the Company maintains net operating loss carryforwards and has established a valuation allowance against the entire net deferred tax asset as of June 30, 2012. No share-based compensation expense was capitalized on our Consolidated Balance Sheets as of June 30, 2012 and December 31, 2011.

The following table summarizes the activity relating to the Company’s options to purchase common stock for the six month period ended June 30, 2012:

	Option Shares Outstanding			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balance at December 31, 2011		934,816		$	4.88
Granted		806,698			23.58
Exercised		(13,510	)		3.12
Forfeited		(9,806	)		3.28
Balance at June 30, 2012		1,718,198		$	13.68		9.04	$	15,697,604
Vested and expected to vest at June 30, 2012		1,538,488		$	13.01		8.99	$	14,959,224
Vested at June 30, 2012		304,425		$	1.87		7.88	$	6,031,082

The aggregate intrinsic value in the table above represents the pretax intrinsic value, based on our closing stock price of $21.68 as of June 30, 2012, which would have been received by the option holders had all option holders with in-the-money options exercised their options as of that date.

	Three Months Ended June 30,
	2012		2011
Weighted-average grant-date fair value per share	$	12.60	$	9.18
Intrinsic value of options exercised	$	162,845	$	5,423
Cash received from stock option exercises	$	32,108	$	892,221

	Six Months Ended June 30,
	2012		2011
Weighted-average grant-date fair value per share	$	15.02	$	9.24
Intrinsic value of options exercised	$	223,319	$	5,423
Cash received from stock option exercises	$	42,149	$	893,670

The 2009 Equity Incentive Plan allows for the option holder to exercise stock option shares prior to the vesting of the option. The shares acquired from an early exercise are subject to repurchase if the option holder terminates employment or service with the Company. The number of unvested common shares at the point of termination will be repurchased by the Company at the stated exercise price of the option. The number of common shares exercised prior to vesting was 251,471 and 336,545 at June 30, 2012 and 2011, respectively. The number of early exercised shares expected to vest using estimated forfeiture rates over the remaining service period of the option term was 249,100 and 284,105 at June 30, 2012 and 2011, respectively.

As of June 30, 2012, the unrecognized share-based compensation expense related to nonvested options, adjusted for expected forfeitures, and estimated weighted-average remaining vesting period was as follows:

Unrecognized share-based compensation expense             (in millions)	Weighted- average remaining vesting period             (in years)
$                14.6	3.2