Goodwill and Other Intangible Assets (Goodwill And Other Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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	(87,965)		(87,965)		(83,341)	(76,585)
Other intangible assets, amortization	(1,541)	$ (1,689)	(4,624)	$ (5,067)	(6,756)
Other intangible assets, net	$ 25,506		$ 25,506		$ 30,130	$ 36,886