STOCK-BASED COMPENSATION - Expense Included in Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	$ 80,909	$ 63,862	$ 53,313
Income tax benefit	(16,392)	(13,383)	(12,113)
Cost of revenues
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	18,822	16,862	14,573
Selling and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	32,665	23,237	15,720
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	18,938	15,274	13,618
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	$ 10,484	$ 8,489	$ 9,402