Share-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2012

Share-Based Compensation [Abstract]

Share-based compensation expense in condensed consolidated statements of operations

	Three Months Ended September 30,				Nine Months Ended September 30,
	2012		2011		2012		2011
	(In Thousands)				(In Thousands)
Research and development	$	495	$	269	$	1,277	$	820
General and administrative		741		345		1,877		1,023
Total share-based compensation expense	$	1,236	$	614	$	3,154	$	1,843

Fair value per share and Black-Scholes option pricing model

	Nine Months Ended September 30,
	2012			2011
Weighted average fair value of options	$	7.54		$	2.15
Risk-free interest rate		0.87	%		2.07	%
Expected dividend yield		—			—
Expected option term (in years)		5.32			5.20
Expected volatility		79.3	%		75.0	%

Option activity under the equity incentive plans

	Number of Shares			Weighted Average Exercise Price per Share
Options outstanding at December 31, 2011		7,578,612		$	6.25
Granted		1,605,325		$	11.71
Cancelled		(238,318	)	$	11.27
Exercised		(1,279,343	)	$	4.02
Options outstanding at September 30, 2012		7,666,276		$	7.61
Options exercisable at September 30, 2012		5,297,324		$	7.44