Hedging - Notional Amount (Details) - Foreign currency forward contracts - Designated as hedging instruments - Cash flow hedging - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional amount of foreign currency forward contract	$ 672,167	$ 505,218
Euro
Derivative [Line Items]
Notional amount of foreign currency forward contract	460,885	335,179
Australian dollar
Derivative [Line Items]
Notional amount of foreign currency forward contract	87,358	52,820
British pound sterling
Derivative [Line Items]
Notional amount of foreign currency forward contract	76,061	73,460
Canadian dollar
Derivative [Line Items]
Notional amount of foreign currency forward contract	$ 47,863	$ 43,759