Fair Value of Financial Instruments Gains (lossses) on Cash Flow Hedges Reported in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax	$ 814	$ (3,295)
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	198	(1,638)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	$ 1,012	$ (4,933)