Derivative Instruments - Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	$ 9,776	$ 7,804	$ 4,084
Derivative liability, fair value	9,792	19,320	29,877
Derivatives designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	9,157	2,290	2,715
Derivative liability, fair value	5,287	19,129	28,830
Derivatives designated as hedging instruments: | Foreign currency forward exchange contracts | Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	7,399	2,175	1,951
Derivatives designated as hedging instruments: | Foreign currency forward exchange contracts | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	1,758	115	764
Derivatives designated as hedging instruments: | Foreign currency forward exchange contracts | Accrued liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	5,219	15,970	21,624
Derivatives designated as hedging instruments: | Foreign currency forward exchange contracts | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	68	3,159	7,206
Derivatives not designated as hedging instruments: | Foreign currency forward exchange contracts | Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	619	5,514	1,369
Derivatives not designated as hedging instruments: | Foreign currency forward exchange contracts | Accrued liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	$ 4,505	$ 191	$ 1,047