Derivatives and Hedge Accounting- Location of Gain or Loss Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Cost of revenues	$ 162,446	$ 139,649	$ 319,686	$ 277,750
General and administrative expenses	31,228	27,640	63,759	56,906
Selling & marketing expenses	17,647	15,151	35,694	29,103
Depreciation & amortization	12,752	10,582	26,419	21,086
Foreign exchange gain, net	1,202	1,414	2,462	2,029
Reclassification out of Accumulated Other Comprehensive Income | Derivatives Designated as Hedging Instruments | Derivatives in cash flow hedging relationships | Foreign currency exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Cost of revenues	719	1,191	1,250	3,336
General and administrative expenses	106	180	186	511
Selling & marketing expenses	12	17	19	50
Depreciation & amortization	47	79	100	241
Reclassification from AOCI, before tax	884	1,467	1,555	4,138
Reclassification out of Accumulated Other Comprehensive Income | Derivatives not designated as hedging instruments | Foreign currency exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange gain, net	$ 2,923	$ (2,641)	$ 4,319	$ (5,569)