DERIVATIVES (INCOME STATEMENT CLASSIFICATION) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Sales Revenue Services Net	$ 570,974	$ 492,980	$ 453,081	$ 432,213	$ 461,326	$ 395,507	$ 392,515	$ 394,356	$ 1,949,248	$ 1,643,704	$ 1,509,171
Other nonoperating income expense									(18,591)	3,902	$ (11,618)
Designated as Hedging Instruments [Member] | Foreign Exchange [Member] | Cash Flow [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized in other comprehensive income (loss) - effective portion, net of tax:									1,928	(3,085)
Designated as Hedging Instruments [Member] | Foreign Exchange [Member] | Cash Flow [Member] | Reclassification from accumulated other comprehensive income | Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Sales Revenue Services Net									2,618	(4,228)
Not Designated as Hedging Instruments [Member] | Foreign Exchange [Member] | Fair Value [Member] | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Other nonoperating income expense									$ 205	$ 1,773