Derivatives and Hedge Accounting - Summary of Effect of Foreign Currency Exchange Contracts (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in unaudited consolidated statements of income	$ 1,385	$ 637	$ 3,414	$ 1,905
Derivatives in cash flow hedging relationships | Derivatives in hedging relationships | Foreign currency exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives in cash flow hedging relationships	(11,944)	838	(29,187)	12,111
Reclassification out of Accumulated Other Comprehensive Income | Derivatives not Designated as Hedging Instruments | Foreign currency exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in unaudited consolidated statements of income	$ (4,268)	$ (678)	$ (9,837)	$ 2,095