Accumulated Other Comprehensive Income (Schedule of Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of revenue	$ 239,805	$ 217,974	$ 722,675	$ 638,029
Tax expense (benefits)	15,825	21,535	59,327	66,392
Net income	93,214	70,514	291,370	224,979
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest | Foreign currency exchange contracts | Amount of (loss) gain reclassified from accumulated other comprehensive income into income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of revenue	256	(893)	(2,412)	935
Tax expense (benefits)	153	(333)	(476)	348
Net income	$ 103	$ (560)	$ (1,936)	$ 587