Employee Benefit Plans (Summary Of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options
Options Outstanding, beginning balance	46,251	57,972	87,605
Options, Granted	0	0	0
Options, Exercised	(4,921)	(11,721)	(29,633)
Options, Forfeited	0	0	0
Options Outstanding, ending balance	41,330	46,251	57,972
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding, beginning balance	$ 52.74	$ 51.15	$ 47.15
Weighted-Average Exercise Price, Granted	0	0	0
Weighted-Average Exercise Price, Exercised	45.17	44.87	39.31
Weighted-Average Exercise Price, Forfeited	0	0	0
Weighted-Average Exercise Price, Outstanding, ending balance	$ 53.64	$ 52.74	$ 51.15
Options, Exercisable at end of year	21,459	8,063	2,697
Weighted-Average Exercise Price, Exercisable at end of year	$ 50.45	$ 44.48	$ 45.13
Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares	19,871	38,188	55,275	79,718
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	18,317	17,087	24,443
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, Option, Nonvested, Weighted Average Exercise Price	$ 56.97	$ 54.42	$ 51.40	$ 48.08
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	0	0	0
Weighted-Average Exercise Price, Vested during the year	51.66	44.65	40.58
Weighted-Average Exercise Price, Forfeited during the year	$ 0	$ 0	$ 0
Proceeds from stock option exercises	$ 223	$ 526	$ 1,164
Intrinsic value of stock options exercised	93	368	944
Stock-based compensation expense associated with stock options	60	119	178
Income tax benefit recognized related to stock-based compensation	5	$ 12	$ 19
Unrecognized stock-based compensation expense	$ 24
Weighted average period in which the above amount is expected to be recognized	10 months 24 days