Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2016

Stock-Based Compensation

Summary of stock option activity

	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

Schedule of stock-based compensation expense

	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

Schedule of assumptions used for the fair values of employee and director stock options granted

	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