Summary Of Significant Accounting Policies - Foreign Currency (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Foreign currency translation gains (losses) included in Accumulated OCI	$ 16,264	$ (35,943)	$ (12,849)
Foreign currency transaction gains (losses)	$ (2,200)	$ 200	$ (1,200)