ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (INCOME STATEMENT CLASSIFICATION TABLE) (DETAILS) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Presentation of Income Statement Reclassifications [Line Items]
Sales Revenue Services Net	$ 426,623	$ 359,036	$ 353,429	$ 338,277	$ 344,947	$ 312,796	$ 305,105	$ 312,410	$ 1,477,365	$ 1,275,258	$ 1,286,755
Interest Expense.									13,734	7,943	7,538
Benefit from (provision for) income taxes	$ (69,016)	$ (2,071)	$ (1,597)	$ (5,391)	$ (6,196)	$ 813	$ (2,952)	$ (4,528)	(78,075)	(12,863)	(20,004)
Net income									10,812	37,435	65,885
Accumulated Other Comprehensive Income (Loss)
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									14,876	17,931	(8,716)
Derivative Valuation, Net of Tax
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									14,406	16,750	(7,809)
Tax effect
Presentation of Income Statement Reclassifications [Line Items]
Provision for income taxes - Other									52	129	101
Cost of Services
Presentation of Income Statement Reclassifications [Line Items]
Cost of services									522	1,310	1,008
Reclassification from accumulated other comprehensive income
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									470	1,181	907
Reclassification from accumulated other comprehensive income | Derivative Valuation, Net of Tax
Presentation of Income Statement Reclassifications [Line Items]
Net income									(14,406)	(16,750)	(7,809)
Reclassification from accumulated other comprehensive income | Tax effect
Presentation of Income Statement Reclassifications [Line Items]
Benefit from (provision for) income taxes									(8,501)	(11,809)	(5,654)
Foreign Exchange Forward | Reclassification from accumulated other comprehensive income | Foreign Currency Translation Adjustment
Presentation of Income Statement Reclassifications [Line Items]
Sales Revenue Services Net									(22,792)	(28,025)	(12,410)
Interest Rate | Reclassification from accumulated other comprehensive income | Loss on interest rate swaps
Presentation of Income Statement Reclassifications [Line Items]
Interest Expense.									$ (115)	$ (534)	$ (1,053)