EQUITY-BASED COMPENSATION PLANS (NARRATIVE) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Equity-based compensation expense	$ 3,168	$ 3,609
Restricted Stock Units (RSUs) [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Equity-based compensation expense	3,200	$ 3,600
Unrecognized Compensation Expense	$ 21,500
Non-option Equity Awards Granted	10,693	18,128
Cost of Services
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Equity-based compensation expense	$ 1,200	$ 1,300
Selling General And Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Equity-based compensation expense	$ 2,000	$ 2,300