Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

Stock-Based Compensation

Summary of stock option activity

		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options Outstanding at December 31, 2017	10,856,212	$	9.40	6.1
Granted	5,056,467		0.61
Exercised	(104,500)		2.80
Canceled	(2,568,090)		8.76
Options Outstanding at September 30, 2018	13,240,089		6.22	7.4
Options Vested and Expected to Vest at September 30, 2018	12,884,023		6.36	7.3
Options Exercisable at September 30, 2018	6,190,301		10.97	5.2
Shares Available for Grant Under the 2008 Plan	5,096,110

Schedule of stock-based compensation expense

	Three months ended  September 30,				Nine months ended September 30,
	2018		2017		2018		2017
	(In thousands)				(In thousands)
Research and development	$	799	$	1,546	$	3,088	$	5,310
General and administrative		994		1,193		3,241		4,418
Total stock-based compensation expense	$	1,793	$	2,739	$	6,329	$	9,728

Schedule of assumptions used for the fair value of employee stock options granted

	Three months ended  September 30,				Nine months ended September 30,
	2018		2017		2018		2017
Expected stock price volatility	85	%	76	%	73-85	%	76-77	%
Expected option term	6.0	Years	6.0	Years	6.0	Years	6.0	Years
Risk-free interest rate	2.8	%	2.0	%	2.8-3.0	%	2.0-2.3	%
Expected dividend yield	None		None		None		None