Derivatives (Gains (Losses) in Foreign Currency Translation Adjustment) (Details) - Derivative instruments designated as hedging instruments - Net investment hedges - Foreign currency forward contracts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
(Losses) gains recognized in AOCI on net investment hedges (effective portion)	$ (648)	$ 2,908	$ 1,485
(Losses) gains recognized in foreign exchange income (ineffective portion)	$ (1,953)	$ 1,124	$ 880