Goodwill and Other Intangible Assets (Goodwill And Other Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Finite-lived Intangible Assets [Roll Forward]
Other intangible assets, gross	$ 113,471		$ 113,471		$ 113,471	$ 113,471
Other intangible assets, accumulated amortization	(86,424)		(86,424)		(83,341)	(76,585)
Other intangible assets, amortization	(1,542)	$ (1,689)	(3,083)	$ (3,378)	(6,756)
Other intangible assets, net	$ 27,047		$ 27,047		$ 30,130	$ 36,886