Stock-Based Compensation

9 Months Ended

Sep. 30, 2016

Stock-Based Compensation

Stock-Based Compensation

(11)  Stock-Based Compensation

A summary of stock option activity for the nine months ended September 30, 2016 is as follows:

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2015	8,110,239		$	13.13	6.7
Granted	2,314,550		$
Exercised	(47,942	)	$
Canceled	(226,249	)	$
Options Outstanding at September 30, 2016	10,150,598		$	11.26	6.7
Options Vested and Expected to Vest at September 30, 2016	10,071,300		$	11.26	6.7
Options Exercisable at September 30, 2016	5,871,345		$	10.54	5.1
Shares Available for Grant under the 2008 Plan	3,641,582

The weighted average grant-date fair value of stock options granted during the nine months ended September 30, 2016 was $3.22 per share. Stock-based compensation expense for the three and nine months ended September 30, 2016 and 2015 was recorded as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2016		2015		2016		2015
	(In thousands)
Research and development	$	2,042	$	1,715	$	5,866	$	4,228
General and administrative	1,754		2,153		5,843		4,449
Total stock-based compensation expense	$	3,796	$	3,868	$	11,709	$	8,677

The fair values of employee and director stock options granted during the three and nine months ended September 30, 2016 and 2015 were valued using the Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2016		2015		2016	2015
Expected stock price volatility	76	%	67	%	70 - 77%	67 - 69%
Expected option term	6.0 years		6.0 years		6.0 years	6.0 years
Risk-free interest rate	1.4	%	1.9	%	1.4 - 1.6%	1.8 - 2.2%
Expected dividend yield	None		None		None	None