STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 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		2,464,750		$	4.78
Exercised		(48,817	)	$	2.90
Canceled		(307,462	)	$	14.05
Options Outstanding at December 31, 2016		10,218,710		$	11.14		6.5
Options Vested and Expected to Vest at December 31, 2016		10,148,728		$	11.14		6.5
Options Exercisable at December 31, 2016		6,086,840		$	10.86		5.0
Shares Available for Grant under the 2008 Plan		3,577,635

Summary of restricted stock activity

	Shares			Weighted Average Grant Date Fair Value (per share)
Outstanding and unvested at December 31, 2015		19,500		$	25.41
Granted		60,000		$	4.72
Vested		(19,500	)	$	25.41
Canceled		(10,000	)	$	4.72
Outstanding and unvested at December 31, 2016		50,000		$	4.72

Schedule of stock-based compensation expense

	2016		2015		2014
	(In thousands)
Research and development	$	7,821	$	6,186	$	3,459
General and administrative		7,496		6,588		3,393
Total stock-based compensation expense	$	15,317	$	12,774	$	6,852

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

	Year Ended December 31, 2016	Year Ended December 31, 2015	Year Ended December 31, 2014
Expected stock price volatility	70 - 77%	67 - 69%	70 - 72%
Expected option term	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	1.4 - 2.3%	1.8 - 2.2%	1.9 - 2.2%
Expected dividend yield	None	None	None