Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2014

Stock-based Compensation [Abstract]

Weighted average assumptions

The fair value of the stock options granted was estimated based on the following weighted average assumptions for three months ended March 31, 2014 and 2013:

	Three Months Ended March 31,
	2014			2013
Dividend yield		0	%		0	%
Expected volatility		94	%		92	%
Risk-free interest rate		1.73	%		0.78	%
Expected term	5.6 years			5.6 years

Stock option activity

Stock option activity for the three months ended March 31, 2014 was as follows:

	Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Options outstanding at December 31, 2013		7,218,241		$	8.42		6.75	$	18,213
Granted		1,099,239			8.56
Exercised		(640,649	)		4.72
Forfeited, expired or cancelled		(116,766	)		24.72
Options outstanding at March 31, 2014		7,560,065		$	8.50		7.14	$	9,892
Options exercisable at March 31, 2014		4,562,868		$	10.85		5.95	$	5,422

Unvested RSU activity

Unvested RSU activity for the three months ended March 31, 2014 is summarized below:

				Weighted-
	Number of			Average Grant-
	Shares			Date Fair Value
Unvested balance at December 31, 2013		1,738,037		$	2.73
Granted		972,614			8.64
Vested		(478,845	)		4.16
Forfeited		(77,536	)		2.82
Unvested balance at March 31, 2014		2,154,270		$	5.08

Stock-based compensation expense

The following table shows total stock-based compensation expense included in the condensed consolidated statements of comprehensive loss for the three months ended March 31, 2014 and 2013 (in thousands):

	Three Months Ended March 31,
	2014		2013
Research and development	$	2,406	$	997
Selling, general and administrative		1,518		622
Total stock-based compensation expense	$	3,924	$	1,619