STOCK BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2017

STOCK BASED COMPENSATION

Schedule of stock-based compensation expense

	Year Ended December 31,
(In thousands)	2017		2016		2015
Research and development	$	697	$	632	$	1,036
General and administrative		9,136		7,665		5,837
Total stock-based compensation expense	$	9,833	$	8,297	$	6,873

Schedule of stock-based compensation expense included in the consolidated statements of operations by award type

	Year Ended December 31,
(In thousands)	2017		2016		2015
Stock options	$	593	$	632	$	789
RSUs		2,282		1,920		2,492
RSAs		4,497		3,492		2,850
Performance-based RSAs		242		1,293		613
Market-based RSUs		291		112		—
Market-based RSAs		1,855		693		—
ESPP		73		155		129
Total stock-based compensation expense	$	9,833	$	8,297	$	6,873

Schedule of unrecognized stock-based compensation cost and the estimated weighted-average amortization period

        As of December 31, 2017, the unrecognized stock-based compensation cost and the estimated weighted-average amortization period were as follows:

(In thousands)	Unrecognized Compensation Cost		Weighted-Average Amortization Period (Years)
Stock options	$	305		0.5
RSUs		1,487		0.9
RSAs		7,764		2.4
Market-based RSUs		285		0.9
Market-based RSAs		1,943		1.0
Total unrecognized compensation cost	$	11,784

Summary of equity award activity under the 2012 plan and prior plans

(In thousands, except per share data)	Number of outstanding options			Weighted- Average Exercise Price of Outstanding Options		Number of outstanding RSUs and PSUs			Weighted- Average Fair Value per Share at Grant		Number of outstanding RSAs and PSAs			Weighted- Average Fair Value per Share at Grant
Balance as of December 31, 2016		2,900		$	23.72		413		$	15.29		1,125		$	13.67
Granted		—			—		255			11.38		774			9.53
Exercised		(16	)		11.81		—			—		—			—
Released RSUs/RSAs		—			—		(278	)		15.88		(412	)		14.87
Forfeited		(1,244	)		23.63		(20	)		12.62		(39	)		13.19
Balance as of December 31, 2017		1,640			23.90		370			11.57		1,448			9.95

Schedule of weighted-average assumptions used to estimate the fair value of stock options granted and employee stock purchase plan issuances

	Year Ended December 31,
	2017	2016	2015
Employee stock purchase plan issuances
Risk-free interest rate	1.4% - 1.7%	0.4% - 1.0%	0.1% - 0.9%
Expected term (in years)	0.5 - 2	0.5 - 2	0.5 - 2
Volatility	35% - 44%	39% - 66%	44% - 69%
Dividend yield	0%	0%	0% - 6%
Weighted-average estimated fair value of ESPP shares granted	$3.90	$4.47	$4.52