Derivatives and Hedging Activities Derivative Balance Sheet Location (Details) - Foreign Exchange Forward [Member] - Designated as Hedging Instrument [Member] $ in Thousands	Dec. 31, 2017 USD ($)
Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	$ 187
Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	402
Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	$ 589