STOCKHOLDERS' EQUITY (Tables)

12 Months Ended

Dec. 31, 2015

STOCKHOLDERS' EQUITY

Schedule of aggregate option and award activity

				Outstanding Options
	Shares Available For Grant			Number of Shares			Weighted Average Exercise Price Per Share	Weighted Average Remaining Contractual Life (In years)	Aggregate Intrinsic Value (In thousands)
Balance at December 31, 2014		13,384,883			16,958,944		$3.16		$16,038
Options granted		(2,875,000	)		2,875,000		$4.29
Awards granted		(14,015	)		—		$   —
Options exercised		—			(1,069,838	)	$2.06
Options cancelled/forfeited		1,558,423			(1,558,423	)	$4.65
Awards cancelled/forfeited		625			—		$   —
Balance at December 31, 2015		12,054,916			17,205,683		$3.29	6.89	$29,267
Options exercisable at December 31, 2015					11,356,232		$2.98	6.18	$23,234
Options fully vested and expected to vest at December 31, 2015					16,703,236		$3.26	6.84	$28,932

Schedule of information about stock options outstanding by exercise price range

        Information about stock options outstanding as of December 31, 2015 is as follows:

	Options Outstanding
Exercise Price Range	Number of Shares		Weighted Average Exercise Price Per Share	Weighted Average Remaining Contractual Life (In years)
$1.10 - $1.51		6,003,210	$1.45	6.58
$1.55 - $4.34		5,412,577	$3.21	7.63
$4.42 - $5.09		4,744,005	$4.99	7.41
$5.14 - $9.32		1,045,891	$6.47	2.45
$1.10 - $9.32		17,205,683	$3.29	6.89

Schedule of aggregate restricted stock activity

	Number of Shares			Weighted Average Grant Date Fair Value Per Share	Weighted Average Remaining Contractual Term (In years)
Non-vested restricted stock at December 31, 2014		60,970		$4.73	0.37
Granted		14,015		$3.75
Vested		(73,860	)	$4.54
Cancelled/forfeited		(625	)	$4.65
Non-vested restricted stock at December 31, 2015		500		$4.65	0.10

Summary of allocation of stock-based compensation expense related to share-based payment awards

	Year Ended December 31,
(In thousands)	2015		2014		2013
Research and development	$	2,139	$	2,545	$	1,741
Restructuring charges		307		—		28
General and administrative		5,951		5,113		2,666
Stock-based compensation expense included in operating expenses	$	8,397	$	7,658	$	4,435

Schedule of assumptions used to estimate the fair value of stock options granted

	2015	2014	2013
Dividend yield	0%	0%	0%
Expected volatility range	0.874 to 0.884	0.898 to 0.922	0.742 to 0.792
Risk-free interest rate range	1.68% to 1.71%	1.64% to 1.92%	0.80% to 1.97%
Expected term	5.5 yrs	5.5 yrs	6 yrs

Schedule of assumptions used to estimate the fair value of employee stock purchases under the Purchase Plans

	2015	2014	2013
Dividend yield	0%	0%	0%
Expected volatility range	0.654 to 1.392	0.835 to 1.666	0.506 to 1.391
Risk-free interest rate range	0.11% to 0.28%	0.06% to 0.15%	0.09% to 0.21%
Expected term range	6 mos to 12 mos	6 mos to 12 mos	6 mos to 12 mos

Schedule of common stock reserved for future issuance

        Common stock reserved for future issuance as of December 31, 2015 is as follows:

Outstanding stock options	17,205,683
Options and awards available for grant	12,054,916
Employee stock purchase plan	942,365
Warrants outstanding	537,893
Total	30,740,857