STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2019

STOCK-BASED COMPENSATION [Abstract]

Grants in Period, Weighted Average Grant Date Fair Value

The weighted average grant date fair value per share of the options awarded to employees were as follows:

	Year Ended
	December 31,
	2019		2018		2017
Weighted average grant date fair value per share	$	13.76	$	14.90	$	9.12

Summary of Stock Option Activity

Stock option activity during the year ended December 31, 2019 is summarized as follows:

	Option ‎Shares (thousands)	Weighted ‎average ‎exercise ‎price		Weighted ‎average ‎remaining ‎contractual ‎life (years)	Aggregate ‎intrinsic ‎value ‎(thousands)
Outstanding at December 31, 2018	9,668	$	31.45
Granted	2,920		46.55
Exercised	(1,251)		24.86
Forfeited	(687)		40.08
Outstanding at December 31, 2019	10,650	$	35.80	7.3	$	245,781
Exercisable at December 31, 2019	5,063	$	27.44	6.0	$	159,155
Expected to vest at December 31, 2019	5,587	$	43.37	8.5	$	86,625

Intrinsic Value and Stock-based Compensation Schedule

Compensation expense related to stock options granted to employees and non-employees under the Plans and the intrinsic value of stock options exercised was as follows:

	Year Ended
	December 31,
(In thousands)	2019		2018		2017
Intrinsic value of stock options exercised	$	31,315	$	59,345	$	12,217
Stock-based compensation expense	$	26,085	$	21,899	$	14,686
Net stock-based compensation capitalized into inventory		331		320		196
Total stock-based compensation cost	$	26,416	$	22,219	$	14,882

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

The fair value of the options was estimated on the date of the grant using a Black-Scholes option pricing model with the following assumptions:

	Year Ended
	December 31,
	2019			2018			2017
Risk-free interest rate	1.35%	-	2.57%	2.30%	-	3.09%	1.74%	-	2.20%
Expected term (years)	5.0			5.8	-	7.5	5.8	-	6.4
Expected volatility	29.0%			23.0%	-	28.0%	26.0%	-	29.0%
Expected dividend yield		—%			—%			—%