Hedging - Offsetting Derivatives (Details) - Cash flow hedging - Foreign currency forward contracts - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Offsetting Derivative Assets [Abstract]
Gross Amounts Recognized	$ 14,616	$ 13
Offsetting Derivative Liabilities [Abstract]
Gross Amounts Recognized	(571)	(14,508)
Designated as hedging instruments
Offsetting Derivative Assets [Abstract]
Gross Amounts Recognized	14,616	13
Gross Amounts Offset	0	0
Gross Amounts Presented	14,616	13
Gross Amounts Not Offset	(571)	(13)
Legal Offset	14,045	0
Offsetting Derivative Liabilities [Abstract]
Gross Amounts Recognized	(571)	(14,508)
Gross Amounts Offset	0	0
Gross Amounts Presented	(571)	(14,508)
Gross Amounts Not Offset	571	13
Legal Offset	$ 0	$ (14,495)

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