Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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, 2016		10,218,710		$	11.14		6.5
Granted		2,427,200		$	2.37
Exercised		—		$	—
Canceled		(1,789,698	)	$	9.76
Options Outstanding at December 31, 2017		10,856,212		$	9.40		6.1
Options Vested and Expected to Vest at December 31, 2017		10,780,023		$	9.43		6.1
Options Exercisable at December 31, 2017		6,846,254		$	11.18		4.5
Shares Available for Grant Under the 2008 Plan		8,324,310

Summary of restricted stock activity

	Shares			Weighted Average Grant Date Fair Value (per share)
Outstanding and unvested at December 31, 2016		50,000		$	4.72
Granted		70,000		$	2.32
Vested		(16,665	)	$	4.72
Canceled		(6,667	)	$	4.72
Outstanding and unvested at December 31, 2017		96,668		$	2.98

Schedule of stock-based compensation expense

	2017		2016		2015
	(In thousands)
Research and development	$	6,693	$	7,821	$	6,186
General and administrative		5,619		7,496		6,588
Total stock-based compensation expense	$	12,312	$	15,317	$	12,774

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

	2017	2016	2015
Expected stock price volatility	75 - 77%	70 - 77%	67 - 69%
Expected option term	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	2.0 - 2.3%	1.4 - 2.3%	1.8 - 2.2%
Expected dividend yield	None	None	None