Derivatives and Hedge Accounting - Summary of Effect of Foreign Currency Exchange Contracts (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
(Gain)/loss recognized in unaudited consolidated statements of income	$ (1,414)	$ (886)	$ (2,029)	$ (1,268)
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	12,229	(2,243)	17,243	(11,272)
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	$ 2,641	$ (151)	$ 5,569	$ (2,773)