Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2014

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees

The assumptions used to estimate the fair value of options granted to employees at the date of grant for the three months ended March 31, 2014 and 2013 were as follows:

	Three months ended March 31,
	2014			2013
Risk-free interest rate		1.9	%		1.1	%
Expected dividend yield		0	%		0	%
Expected term		5.8-5.9 years			5.8-5.9 years
Expected volatility		70	%		67	%

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense as follows for the three months ended March 31, 2014 and 2013:

	Three months ended March 31,
(in thousands)	2014			2013
Employee awards:
Research and development	$	1,681		$	1,284
General and administrative		1,292			1,090
Stock-based compensation for employee awards		2,973			2,374
Stock-based compensation for non-employee awards		(37	)		12
Total stock-based compensation	$	2,936		$	2,386

Summary of Stock Option Activity

The following table summarizes stock option activity during the three months ended March 31, 2014:

Number (in thousands, except per share amounts)	Weighted of Shares			Remaining Average Exercise Price		Aggregate Contractual Term		Intrinsic Value
Outstanding, December 31, 2013		20,107		$	3.93		6.11	$	38,348
Granted		2,810		$	5.02
Exercised		(521	)	$	2.06
Forfeited		(153	)	$	6.11
Outstanding, March 31, 2014		22,243		$	4.09		6.41	$	33,398
Vested and expected to vest, March 31, 2014		21,798		$	4.06		6.35	$	33,365
Exercisable, March 31, 2014		15,769		$	3.36		5.27	$	32,975