Derivative Instruments - Fair Values (Details) - Cash flow hedges - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivatives designated as hedging instruments
Fair value of cash flow hedges
Total asset derivative	$ 2,137	$ 1,651
Total liability derivative	3,446	2,118
Derivatives designated as hedging instruments | Prepaid and other current assets | Foreign currency exchange purchased option contracts
Fair value of cash flow hedges
Total asset derivative		1,024
Derivatives designated as hedging instruments | Prepaid and other current assets | Interest rate swap contracts
Fair value of cash flow hedges
Total asset derivative		220
Derivatives designated as hedging instruments | Other current assets | Interest rate swap contracts
Fair value of cash flow hedges
Total asset derivative	423
Derivatives designated as hedging instruments | Other long-term assets | Foreign currency exchange purchased option contracts
Fair value of cash flow hedges
Total asset derivative	1,230
Derivatives designated as hedging instruments | Other long-term assets | Interest rate swap contracts
Fair value of cash flow hedges
Total asset derivative	484	407
Derivatives designated as hedging instruments | Other long-term liabilities | Foreign currency exchange forward contracts
Fair value of cash flow hedges
Total liability derivative	3,446	2,118
Derivatives not designated as hedging instruments
Fair value of cash flow hedges
Total asset derivative	360	172
Total liability derivative	1,931	1,334
Derivatives not designated as hedging instruments | Prepaid and other current assets | Foreign currency exchange forward contracts
Fair value of cash flow hedges
Total asset derivative	209	124
Derivatives not designated as hedging instruments | Prepaid and other current assets | Foreign currency exchange purchased option contracts
Fair value of cash flow hedges
Total asset derivative	5	3
Derivatives not designated as hedging instruments | Accrued and other current liabilities | Foreign currency exchange forward contracts
Fair value of cash flow hedges
Total liability derivative	1,238	806
Derivatives not designated as hedging instruments | Other long-term assets | Foreign currency exchange forward contracts
Fair value of cash flow hedges
Total asset derivative	94
Derivatives not designated as hedging instruments | Other long-term assets | Foreign currency exchange purchased option contracts
Fair value of cash flow hedges
Total asset derivative	52	45
Derivatives not designated as hedging instruments | Other long-term liabilities | Foreign currency exchange forward contracts
Fair value of cash flow hedges
Total liability derivative	$ 693	$ 528