Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2013

Stock-Based Compensation

Summary of stock option activity

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2012	5,349,810		$	5.98	7.0
Granted	16,500		$	11.96
Exercised	(275,251	)	$	6.00
Canceled	(5,750	)	$	4.34
Options Outstanding at March 31, 2013	5,085,309		$	6.00	6.8
Options Vested and Expected to Vest at March 31, 2013	5,039,443		$	6.01	6.7
Options Exercisable at March 31, 2013	3,158,304		$	6.68	5.5
Shares Available for Grant under the 2008 Plan	3,341,331

Schedule of stock-based compensation expense

	Three months ended March 31,
	2013		2012
	(In thousands)
Research and development	$	441	$	396
General and administrative	267		245
Total stock-based compensation expense	$	708	$	641

Schedule of assumptions used for the fair values of employee stock options granted

	Three months ended March 31,
	2013		2012
Expected stock price volatility	72	%	70	%
Expected option term	6.0 Years		6.0 Years
Risk-free interest rate	1.4	%	1.4	%
Expected dividend yield	None		None