STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of stock-based compensation expense recognized for stock options, stock awards, restricted stock units and the Company's employee stock purchase program (ESPP)

The following table presents stock‑based compensation expense recognized for stock options, RSUs, PSUs, and the ESPP in the Company’s consolidated statements of comprehensive income (in thousands):

	Years Ended December 31,
	2019		2018		2017
Cost of sales	$	106	$	30	$	98
Research and development expenses	693		446		710
Selling, general and administrative expenses	9,797		9,963		12,157
Restructuring charges	—		2,146		51
Total	$	10,596	$	12,585	$	13,016

Schedule of assumptions used to calculate the fair value of option grants

The company used the following assumptions to calculate the fair value of option grants for the years ended December 31, 2019, 2018 and 2017:

	2018	2017
Employee and Director Stock Options
Risk-free interest rate	2.17%	1.65 - 1.93%
Expected option term (in years)	4.34	4.24 - 4.30
Expected stock price volatility	61.94%	51.67 - 59.59%

Schedule of assumptions used to calculate the fair value of stock purchase rights granted under the ESPP

The company used the following assumptions to calculate the fair value of option grants and stock purchase rights granted under the ESPP for the years ended December 31, 2019, 2018 and 2017:

	2019	2018	2017
Employee Stock Purchase Plan
Risk-free interest rate	1.63 - 2.35%	2.05 - 2.50%	1.07 - 1.45%
Expected option term (in years)	0.5	0.5	0.5
Expected stock price volatility	57.2 - 132.2%	56.1 - 58.6%	52.2 - 82.0%

Summary of the options activity

The following tables summarize the activity for the year ended December 31, 2019 under the 2004 Plan:

	Shares		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Options outstanding at December 31, 2018	1,169,412		$	7.57
Options granted	—		—
Options exercised	(13,691	)	1.83
Options forfeited	—		—
Options expired	(810,515	)	—
Options outstanding at December 31, 2019	345,206		$	7.29	2.58	$	—
Options vested and expected to vest at December 31, 2019	345,206		$	7.29	2.58	$	—
Options exercisable at December 31, 2019	345,206		$	7.29	2.58	$	—

The following table summarize the options activity for the year ended December 31, 2019 under the 2014 Plan:

	Number of Shares		Weighted Average Exercise Price		Weighted- Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Options outstanding at December 31, 2018	1,461,469		$	12.90
Options granted	—		—
Options exercised	—		—
Options forfeited	(102,669	)	13.86
Options expired	(180,755	)	14.01
Options outstanding at December 31, 2019	1,178,045		$	12.64	6.15	$	—
Options vested and expected to vest at December 31, 2019	1,178,045		$	12.64	6.15	$	—
Options exercisable at December 31, 2019	892,730		$	13.50	5.77	$	—

Schedule of restricted stock units and performance-based restricted stock units activity

RSUs generally vest over three or four years, with 33% or 25% of each award vesting annually, respectively. The following table summarizes the RSUs activity for the year ended December 31, 2019 under the 2014 Plan:

	Number of Shares		Weighted Average Grant Date Fair  Value Per Share		Weighted Average Remaining Contractual Term (in years)
Non-vested restricted stock units at December 31, 2018	1,938,788		$	6.94
Granted	2,750,408		3.84
Vested	(873,784	)	8.08
Forfeited	(878,697	)	5.40
Non-vested restricted stock units at December 31, 2019	2,936,715		$	4.64	1.05

The following table summarizes the PSU activity for the year ended December 31, 2019 under the 2014 Plan (in thousands, except per share data):

	Number of Shares		Weighted Average Grant Date Fair  Value Per Share		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Non-vested performance-based restricted stock units at December 31, 2018	374,824		$	10.14
Granted	643,266		6.87
Vested	—		—
Forfeited	(34,247	)	6.87
Non-vested performance-based restricted stock units at December 31, 2019	983,843		$	8.11	1.71	$	1,230