Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

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

The assumptions used to estimate the fair value of options granted to employees and directors at the date of grant for the three and nine months ended September 30, 2014 were as follows:

	Three months ended September 30,		Nine months ended September 30,
	2014	2013	2014	2013
Risk-free interest rate	1.8-2.0%	1.9%	1.6-2.0%	0.1-1.9%
Expected dividend yield	0%	0%	0%	0%
Expected term	5.8-5.9 years	5.9 years	5.0-5.9 years	5.3-5.9 years
Expected volatility	67-72%	67-68%	64-72%	67-68%

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense as follows for the three and nine months ended September 30, 2014 and 2013:

	Three months ended September 30,					Nine months ended September 30,
(in thousands)	2014		2013			2014		2013
Employee awards:
Research and development	$	1,663	$	1,517		$	5,185	$	4,453
General and administrative		1,143		1,212			4,596		3,609
Stock-based compensation for employee awards		2,806		2,729			9,781		8,062
Stock-based compensation for non-employee awards		44		(192	)		160		(109	)
Total stock-based compensation	$	2,850	$	2,537		$	9,941	$	7,953

Summary of Stock Option Activity

The following table summarizes stock option activity during the nine months ended September 30, 2014:

(in thousands, except per share amounts and years)	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding, December 31, 2013		20,107		$	3.93		6.11	$	38,348
Granted		3,704		$	5.45
Exercised		(2,793	)	$	2.27
Forfeited		(471	)	$	6.30
Outstanding, September 30, 2014		20,547		$	4.37		6.38	$	90,628
Vested and expected to vest, September 30, 2014		20,220		$	4.35		6.33	$	89,628
Exercisable, September 30, 2014		15,313		$	3.84		5.50	$	75,699