STOCK-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Stock-Based Compensation Expense

Compensation expense included in the Company’s Condensed Consolidated Statements of Comprehensive Loss for all stock-based compensation arrangements was as follows: 

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Cost of sales	$	3,717	$	3,246	$	8,536	$	6,386
R&D	14,943		15,573		28,776		28,842
Selling, general and administrative	21,169		19,787		45,278		39,986
Total stock-based compensation expense	$	39,829	$	38,606	$	82,590	$	75,214

Schedule of Stock Option Valuation Assumptions

The assumptions used to estimate the per share fair value of stock options granted during the periods presented were as follows: 

	Three Months Ended June 30,		Six Months Ended June 30,
	2019	2018	2019	2018
Expected volatility	37.1 – 37.2%	38.4%	37.1 – 37.4%	37.8 – 38.4%
Dividend yield	0.0%	0.0%	0.0%	0.0%
Expected life (in years)	5.8	5.7	4.6 – 5.8	4.6 – 5.7
Risk-free interest rate	2.2 – 2.4%	2.7%	2.2 – 3.0%	2.3 – 2.7%