Derivative Financial Instruments, Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type (Details) - Foreign Exchange Forward [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Oct. 01, 2017
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Net unrealized gain	$ 532	$ (2,891)	$ 1,253
Not Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Unrealized gains	2,060	0	2,606
Unrealized losses	(1,452)	0	(1,353)
Net unrealized gain	608	0	1,253
Not Designated as Hedging Instrument [Member] | Accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Unrealized gains	12	1,793	0
Unrealized losses	(33)	(4,684)	0
Net unrealized gain	(21)	(2,891)	0
Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Unrealized gains	30	0	0
Unrealized losses	(85)	0	0
Net unrealized gain	(55)	0	0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Net unrealized gain	17,434	(7,934)	(11,949)
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Unrealized gains	15,414	13,666	10,207
Unrealized losses	(4,079)	(10,319)	(7,977)
Net unrealized gain	11,335	3,347	2,230
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Unrealized gains	9,591	11,255	11,631
Unrealized losses	(1,455)	(2,376)	(3,139)
Net unrealized gain	8,136	8,879	8,492
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Unrealized gains	596	4,215	5,354
Unrealized losses	(1,182)	(15,484)	(20,999)
Net unrealized gain	(586)	(11,269)	(15,645)
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Unrealized gains	1,035	4,546	8,325
Unrealized losses	(2,486)	(13,437)	(15,351)
Net unrealized gain	$ (1,451)	$ (8,891)	$ (7,026)