Financial Instruments And Risk Management (Balance Sheet Classification And Fair Value Of Derivative Instruments) (Details) - Currency Forward Contracts [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Prepaid Expenses And Other Current Assets [Member] | Derivative Instruments Designated As Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	$ 7,262	$ 1,648	$ 1,930
Prepaid Expenses And Other Current Assets [Member] | Derivative Instruments Not Designated As Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	865	683	959
Other Non-Current Assets [Member] | Derivative Instruments Designated As Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative assets	7,963	335	509
Accrued Liabilities [Member] | Derivative Instruments Designated As Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	584	9,336	10,152
Accrued Liabilities [Member] | Derivative Instruments Not Designated As Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	154	1,229	407
Other Long Term Liabilities [Member] | Derivative Instruments Designated As Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities	$ 0	$ 3,820	$ 3,048