ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (INCOME STATEMENT CLASSIFICATION TABLE) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Presentation of Income Statement Reclassifications [Line Items]
Sales Revenue Services Net	$ 461,326	$ 395,507	$ 392,515	$ 394,356	$ 419,133	$ 364,936	$ 349,853	$ 375,249	$ 1,643,704	$ 1,509,171	$ 1,477,365
Interest Expense.									19,113	28,674	13,734
Benefit from (provision for) income taxes	$ (5,670)	$ (5,196)	$ (7,345)	$ (7,466)	$ (11,835)	$ (1,893)	$ (653)	$ (2,102)	(25,677)	(16,483)	(78,075)
Net income									84,734	39,755	10,812
Accumulated Other Comprehensive Income (Loss)
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									3,283	13,214	14,876
Tax effect
Presentation of Income Statement Reclassifications [Line Items]
Provision for income taxes - Other									23	42	52
Derivative Valuation, Net of Tax
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									3,085	12,810	14,406
Cost of Services
Presentation of Income Statement Reclassifications [Line Items]
Cost of services									(221)	(446)	(522)
Reclassification from accumulated other comprehensive income
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									(198)	(404)	(470)
Reclassification from accumulated other comprehensive income | Tax effect
Presentation of Income Statement Reclassifications [Line Items]
Benefit from (provision for) income taxes									1,143	4,738	8,501
Reclassification from accumulated other comprehensive income | Derivative Valuation, Net of Tax
Presentation of Income Statement Reclassifications [Line Items]
Net income									(3,085)	(12,810)	(14,406)
Foreign Exchange Forward | Reclassification from accumulated other comprehensive income | Foreign Currency Translation Adjustment
Presentation of Income Statement Reclassifications [Line Items]
Sales Revenue Services Net									$ (4,228)	$ (17,548)	(22,792)
Interest Rate | Reclassification from accumulated other comprehensive income | Loss on interest rate swaps
Presentation of Income Statement Reclassifications [Line Items]
Interest Expense.											$ (115)