Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2015

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 months ended March 31, 2015 were as follows:

	Three months ended March 31, 2015
Risk-free interest rate		1.6-1.8	%
Expected dividend yield		0	%
Expected term		5.9 years
Expected volatility		67	%

Schedule of Recognized Stock-Based Compensation Expense

Company recognized stock-based compensation expense as follows for the three months ended March 31, 2015 and 2014:

	Three months ended March 31,
(in thousands)	2015		2014
Employee awards:
Research and development	$	1,967	$	1,681
General and administrative		1,377		1,292
Stock-based compensation for employee awards		3,344		2,973
Stock-based compensation for non-employee awards		26		(37	)
Total stock-based compensation	$	3,370	$	2,936

Summary of Stock Option Activity

The following table summarizes stock option activity during the three months ended March 31, 2015:

(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, 2014		19,556		$	4.47		6.17	$	133,599
Granted		2,276		$	9.09
Exercised		(1,464	)	$	2.14
Forfeited		(83	)	$	5.69
Outstanding, March 31, 2015		20,285		$	5.15		6.55	$	136,489
Vested and expected to vest, March 31, 2015		19,937		$	5.11		6.51	$	134,914
Exercisable, March 31, 2015		14,302		$	4.33		5.53	$	107,983