Stock-Based Compensation

9 Months Ended

Sep. 30, 2014

Stock-Based Compensation

Stock-Based Compensation

(10)  Stock-Based Compensation

A summary of stock option activity for the nine months ended September 30, 2014 is as follows:

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2013	5,770,544		$	8.17	7.0
Granted	1,405,350		$	13.65
Exercised	(167,303	)	$	6.04
Canceled	(9,170	)	$	10.70
Options Outstanding at September 30, 2014	6,999,421		$	9.32	7.0
Options Vested and Expected to Vest at September 30, 2014	6,937,665		$	9.28	7.0
Options Exercisable at September 30, 2014	3,878,159		$	6.92	5.4
Shares Available for Grant under the 2008 Plan	694,762

The weighted average grant-date fair value of stock options granted during the nine months ended September 30, 2014 was $8.81 per share. Stock-based compensation expense for the three and nine months ended September 30, 2014 and 2013 was recorded as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2014		2013		2014		2013
	(In thousands)
Research and development	$	977	$	1,326	$	2,315	$	2,190
General and administrative	981		690		2,404		1,210
Total stock-based compensation expense	$	1,958	$	2,016	$	4,719	$	3,400

The fair values of employee and director stock options granted during the three and nine months ended September 30, 2014 and 2013 were valued using the Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2014		2013		2014		2013
Expected stock price volatility	72	%	72	%	71 - 72	%	72	%
Expected option term	6.0 years		6.0 years		6.0 years		6.0 years
Risk-free interest rate	2.1 - 2.2	%	1.9 - 2.0	%	2.1 - 2.2	%	1.2 - 2.0	%
Expected dividend yield	None		None		None		None