Derivative Financial Instruments Derivative Instruments and Hedging Activities - FV of Derivative Instruments Included Within Consolidated Balance Sheet (Details) - Foreign Exchange Forward [Member] - Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Prepaid Expenses and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	$ 885	$ 0
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	94	0
Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	0	187
Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	0	402
Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	$ 979
Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		$ 589