Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2013

Stock-Based Compensation

Schedule of assumptions used to calculate fair value of options granted to employees

	Three months ended September 30,		Nine months ended September 30,
	2012	2013	2012	2013
Risk-free interest rate	0.7-0.9%	1.9%	0.7-1.1%	0.1-1.9%
Expected dividend yield	0%	0%	0%	0%
Expected term	5.3-5.9 years	5.9 years	5.3-5.9 years	5.3-5.9 years
Expected volatility	66-68%	67-68%	66-72%	67-68%

Schedule of recognized stock-based compensation expense

	Three months ended September 30,					Nine months ended September 30,
(in thousands)	2012		2013			2012		2013
Employee awards:
Research and development	$	1,119	$	1,517		$	2,972	$	4,453
General and administrative	681		1,212			1,544		3,609
Stock-based compensation for employee awards	1,800		2,729			4,516		8,062
Stock-based compensation for non-employee awards	383		(192		)	416		(109		)
Total stock-based compensation	$	2,183	$	2,537		$	4,932	$	7,953

Summary of stock option activity

(in thousands, except per share amounts)	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
Outstanding, December 31, 2012	18,066		$	3.50	6.54	$	51,486
Granted	3,212		$	6.12
Exercised	(665	)	$	2.34
Forfeited	(258	)	$	6.08
Outstanding, September 30, 2013	20,355		$	3.91	6.36	$	20,411
Exercisable, September 30, 2013	15,243		$	3.02	5.45	$	20,336
Vested and expected to vest, September 30, 2013	20,007		$	3.87	6.31	$	20,406