STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2020

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

For 2020, 2019, and 2018, the fair value of each option grant was estimated using the Black-Scholes option-pricing model, using the following assumptions:

	Years Ended December 31,
	2020	2019	2018
Expected option life (years)	5.50 - 6.25	5.50 - 6.25	5.48 - 6.25
Risk-free interest rate	0.31% - 1.63%	1.91% - 2.58%	2.64% - 2.93%
Expected stock price volatility	49.2% - 51.2%	63.1% - 66.7%	55.1% - 60.6%
Dividend yield	—	—	—

Summary of Stock option and restricted stock activity

A summary of stock option activity under the 2008 Plan and Inducement Grant during the years ended December 31, 2020, 2019, and 2018 is presented below:

				Weighted		Weighted
				Average		Average
		Weighted		Grant-		Remaining
(in thousands, except per share and	Option	Average		date		Term	Aggregate
remaining term data)	Shares	Exercise Price		Fair Value		(years)	Intrinsic Value
Outstanding December 31, 2017	767	$	42.93			7.8	$	16,785
Granted	156		57.60	$	31.76
Exercised	(142)		19.47					5,863
Forfeited	(18)		60.17
Expired	(4)		74.53
Outstanding December 31, 2018	759	$	49.74			7.6	$	2,221
Granted	160		65.97	$	40.14
Exercised	(130)		41.99					3,335
Forfeited	(31)		56.66
Expired	(1)		54.36
Outstanding at December 31, 2019	757	$	54.21			7.2	$	6,761
Granted	231		30.29	$	14.39
Exercised	(8)		36.81					216
Forfeited	(44)		54.54
Expired	—		—
Outstanding at December 31, 2020	936	$	48.44			7.1	$	372
Exercisable at December 31, 2020	571	$	53.06			5.9	$	347

Non-vested Restricted Stock Shares Activity

A summary of RSA activity under the Plan during the years ended December 31, 2020, 2019, and 2018 is presented below:

		Weighted
		Average Grant		Weighted Average
(in thousands, except per share and		Date Fair		Remaining Term
remaining term data)	Shares	Value		(years)
Unvested at December 31, 2017	85	$	48.34	2.6
Granted	65		58.11
Vested	(33)		47.34
Forfeited	—		—
Unvested at December 31, 2018	117	$	54.04	2.1
Granted	122		66.39
Vested	(42)		54.77
Forfeited	(5)		62.63
Unvested at December 31, 2019	192	$	61.46	2.6
Granted	305		44.42
Vested	(127)		58.88
Forfeited	(18)		51.53
Unvested at December 31, 2020	352	$	48.14	2.7

Employee Stock Purchase Plan 2016 [Member]

Summary of allocated expense

(in thousands)	Years Ended December 31,
	2020		2019		2018
Cost of sales	$	21	$	18	$	11
Research and development		36		29		16
Selling, general, and administrative		123		100		75
	$	180	$	147	$	102

Stock Incentive Plan 2008 [Member]

Summary of allocated expense

	Years Ended December 31,
(in thousands)	2020		2019		2018
Cost of sales	$	115	$	101	$	87
Research and development		561		756		771
Selling, general, and administrative		12,080		8,213		5,822
	$	12,756	$	9,070	$	6,680