Derivative Financial Instruments (Gains / Losses on Foreign Currency Derivatives) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Foreign currency transaction gains	$ 2,284	$ 10,814	$ 3,980
Foreign currency forward exchange contracts losses	(1,721)	(13,268)	(7,312)
Foreign currency gain (loss), net	$ 563	$ (2,454)	$ (3,332)