ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (INCOME STATEMENT CLASSIFICATION TABLE) (DETAILS) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Presentation of Income Statement Reclassifications [Line Items]
Sales Revenue Services Net	$ 344,947	$ 312,796	$ 305,105	$ 312,410	$ 341,816	$ 309,195	$ 310,223	$ 325,521	$ 1,275,258	$ 1,286,755	$ 1,241,781
Interest Expense.									7,943	7,538	6,946
Benefit from (provision for) income taxes	$ (6,196)	$ 813	$ (2,952)	$ (4,528)	$ (6,566)	$ (1,192)	$ (7,841)	$ (4,405)	(12,863)	(20,004)	(23,042)
Net income									37,435	65,885	77,417
Accumulated Other Comprehensive Income (Loss)
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									17,931	(8,716)	(3,160)
Derivative Valuation, Net of Tax
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									16,750	(7,809)	(2,128)
Tax effect
Presentation of Income Statement Reclassifications [Line Items]
Provision for income taxes - Other									129	101	66
Cost of Services
Presentation of Income Statement Reclassifications [Line Items]
Cost of services									1,310	1,008	1,098
Reclassification from accumulated other comprehensive income
Presentation of Income Statement Reclassifications [Line Items]
Net Income (Loss) - Other									1,181	907	1,032
Reclassification from accumulated other comprehensive income | Derivative Valuation, Net of Tax
Presentation of Income Statement Reclassifications [Line Items]
Net income									(16,750)	(7,809)	(2,128)
Reclassification from accumulated other comprehensive income | Tax effect
Presentation of Income Statement Reclassifications [Line Items]
Benefit from (provision for) income taxes									(11,809)	(5,654)	(1,361)
Foreign Exchange Forward | Reclassification from accumulated other comprehensive income | Foreign Currency Translation Adjustment
Presentation of Income Statement Reclassifications [Line Items]
Sales Revenue Services Net									(28,025)	(12,410)	(2,429)
Interest Rate | Reclassification from accumulated other comprehensive income | Loss on interest rate swaps [Member]
Presentation of Income Statement Reclassifications [Line Items]
Interest Expense.									$ (534)	$ (1,053)	$ (1,060)