Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2014

Disclosure Of Compensation Related Costs Sharebased 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 six months ended June 30, 2014 were as follows:

	Three months ended June 30,		Six months ended June 30,
	2014	2013	2014	2013
Risk-free interest rate	1.6-1.9%	0.1-1.4%	1.6-1.9%	0.1-1.4%
Expected dividend yield	0%	0%	0%	0%
Expected term	5.0-5.9 years	5.3-5.9 years	5.0-5.9 years	5.3-5.9 years
Expected volatility	64-70%	67-68%	64-70%	67-68%

Schedule of Recognized Stock-Based Compensation Expense

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

	Three months ended June 30,				Six months ended June 30,
(in thousands)	2014		2013		2014		2013
Employee awards:
Research and development	$	1,841	$	1,651	$	3,522	$	2,935
General and administrative		2,161		1,307		3,453		2,397
Stock-based compensation for employee awards		4,002		2,958		6,975		5,332
Stock-based compensation for non-employee awards		153		72		116		84
Total stock-based compensation	$	4,155	$	3,030	$	7,091	$	5,416

Summary of Stock Option Activity

The following table summarizes stock option activity during the six months ended June 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		3,107		$	5.17
Exercised		(1,653	)	$	2.34
Forfeited		(316	)	$	6.27
Outstanding, June 30, 2014		21,245		$	4.20		6.29	$	66,353
Vested and expected to vest, June 30, 2014		20,889		$	4.17		6.24	$	65,734
Exercisable, June 30, 2014		15,759		$	3.62		5.35	$	58,220