Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2012

Stock-Based Compensation

Schedule of assumptions used to calculate fair value of options granted

	Three months ended June 30,		Six months ended June 30,
	2011	2012	2011	2012
Risk-free interest rate	2.5%	0.89-1.11%	2.5%	0.89-1.11%
Expected dividend yield	0%	0%	0%	0%
Expected term	5.0-5.9 years	5.8-5.9 years	5.0-5.9 years	5.8-5.9 years
Expected volatility	73%	71-72%	73%	71-72%

Schedule of recognized stock-based compensation expense

	Three months ended June 30,				Six months ended June 30,
(in thousands)	2011		2012		2011		2012
Employee awards:
Research and development	$	933	$	945	$	1,633	$	1,853
General and administrative	1,775		432		2,048		862
Stock-based compensation for employee awards	2,708		1,377		3,681		2,715
Stock-based compensation for non-employee awards	56		33		103		34
Total stock-based compensation	$	2,764	$	1,410	$	3,784	$	2,749

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	294		$	6.73
Exercised	(378	)	$	2.24
Forfeited	(78	)	$	3.42
Outstanding, June 30, 2012	17,455		$	2.63	$	81,093
Exercisable, June 30, 2012	14,529		$	2.27	$	72,740
Vested and expected to vest, June 30, 2012	17,304		$	2.61	$	80,782