Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2012

Stock-Based Compensation

Schedule of assumptions used to calculate fair value of options granted

	Three months ended September 30,		Nine months ended September 30,
	2011	2012	2011	2012
Risk-free interest rate	1.6%	0.7-0.9%	1.6-2.5%	0.9-1.1%
Expected dividend yield	0%	0%	0%	0%
Expected term	5.9 years	5.3-5.9 years	5.0-5.9 years	5.3-5.9 years
Expected volatility	73%	66%-68%	73%	66-72%

Schedule of recognized stock-based compensation expense

	Three months ended September 30,				Nine months ended September 30,
(in thousands)	2011		2012		2011		2012
Employee awards:
Research and development	$	1,021	$	1,119	$	2,654	$	2,972
General and administrative	405		681		2,453		1,544
Stock-based compensation for employee awards	1,426		1,800		5,107		4,516
Stock-based compensation for non-employee awards	363		383		466		416
Total stock-based compensation	$	1,789	$	2,183	$	5,573	$	4,932

Schedule of stock option activity

(in thousands, except per share amounts)	Number of shares		Weighted average exercise price		Aggregate intrinsic value
Outstanding, December 31, 2011	17,617		$	2.56	$	74,329
Granted	3,220		$	7.46
Exercised	(857	)	$	2.17
Forfeited	(168	)	$	4.23
Outstanding, September 30, 2012	19,812		$	3.34	$	119,270
Exercisable, September 30, 2012	14,692		$	2.32	$	103,676
Vested and expected to vest, September 30, 2012	19,414		$	3.29	$	118,313