Financial Instruments and Risk Management (Balance Sheet Classification and Fair Value of Derivative Instruments) (Details) - Forward Contracts [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Not Designated as Hedging Instrument [Member] | Prepaid Expenses And Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	$ 1,797	$ 683
Not Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	970	1,229
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Prepaid Expenses And Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	11,818	1,648
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	9,922	335
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	47	9,336
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Other Long Term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	$ 1	$ 3,820