Financial Instruments - Balance Sheet Location (Details) - Fair Value, Measurements, Recurring [Member] - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets [Abstract]
Foreign currency cash flow hedges - asset	$ 3,158	$ 358
Liabilities [Abstract]
Foreign currency cash flow hedges - liability	$ 1,456	$ 2,243