Stock-Based Compensation

9 Months Ended

Sep. 30, 2015

Stock-Based Compensation

Stock-Based Compensation

(10)  Stock-Based Compensation

A summary of stock option activity for the nine months ended September 30, 2015 is as follows:

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2014	7,015,350		$	9.34	6.6
Granted	1,806,650		$	25.05
Exercised	(660,658	)	$	5.68
Canceled	(63,214	)	$	15.32
Options Outstanding at September 30, 2015	8,098,128		$	13.10	6.9
Options Vested and Expected to Vest at September 30, 2015	8,045,278		$	13.04	6.9
Options Exercisable at September 30, 2015	4,480,232		$	8.25	5.3
Shares Available for Grant under the 2008 Plan	5,842,723

The weighted average grant-date fair value of stock options granted during the nine months ended September 30, 2015 was $15.41 per share. Stock-based compensation expense for the three and nine months ended September 30, 2015 and 2014 was recorded as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
	(In thousands)
Research and development	$	1,715	$	977	$	4,228	$	2,315
General and administrative	2,153		981		4,449		2,404
Total stock-based compensation expense	$	3,868	$	1,958	$	8,677	$	4,719

The fair values of employee and director stock options granted during the three and nine months ended September 30, 2015 and 2014 were valued using the Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Expected stock price volatility	67	%	72	%	67 - 69	%	71 - 72	%
Expected option term	6.0 years		6.0 years		6.0 years		6.0 years
Risk-free interest rate	1.9	%	2.1 - 2.2	%	1.8 - 2.2	%	2.1 - 2.2	%
Expected dividend yield	None		None		None		None