Employee Benefit Plans (Summary Of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Options
Options Outstanding, beginning balance	86,613	95,015	167,554
Options, Granted	17,631	24,348	12,961
Options, Exercised	(16,639)	(32,750)	(81,500)
Options, Forfeited	0	0	(4,000)
Options Outstanding, ending balance	87,605	86,613	95,015
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding, beginning balance	$ 41.08	$ 38.38	$ 36.74
Weighted-Average Exercise Price, Granted	66.32	43.73	46.41
Weighted-Average Exercise Price, Exercised	35.91	35.28	36.63
Weighted-Average Exercise Price, Forfeited	0.00	0.00	31.66
Weighted-Average Exercise Price, Outstanding, ending balance	$ 47.15	$ 41.08	$ 38.38
Options, Exercisable at end of year	7,887	3,000	19,750
Weighted-Average Exercise Price, Exercisable at end of year	$ 37.37	$ 29.45	$ 34.54
Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares	79,718	83,613	75,265	77,804
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	17,631	24,348	12,961
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	21,526	16,000	15,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares	0	0	0
Weighted-Average Exercise Price
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value	$ 48.08	$ 41.47	$ 39.38	$ 36.76
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	66.32	43.73	46.41
Weighted-Average Exercise Price, Vested during the year	37.31	35.09	32.09
Weighted-Average Exercise Price, Forfeited during the year	$ 0.00	$ 0.00	$ 0
Proceeds from stock option exercises	$ 0.6	$ 1.2	$ 3.0
Intrinsic value of stock options exercised	0.5	0.6	0.9
Stock-based compensation expense associated with stock options	0.2	0.2	0.2
Income tax benefit recognized related to stock-based compensation	0.1	$ 0.1	$ 0.1
Unrecognized stock-based compensation expense	$ 0.4
Weighted average period in which the above amount is expected to be recognized	2 years 7 months