STOCK-BASED COMPENSATION - Costs Related To Stock Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 12,730	$ 12,253	$ 23,694	$ 21,387
Cost of revenues
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	4,438	3,765	8,082	6,249
Business acquisitions | Selling, general and administrative expenses
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,970	4,951	5,980	9,443
Organic growth | Selling, general and administrative expenses
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,322	$ 3,537	$ 9,632	$ 5,695