Employee Benefit Plans (Summary Of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Exercised (in shares)	(7,388)	(1,250)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Proceeds from stock option exercises	$ 280	$ 38
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options Outstanding, beginning balance (in shares)	87,605	86,613
Options, Granted (in shares)	0	17,631
Options, Exercised (in shares)	(7,387)	(1,250)
Options Outstanding, ending balance (in shares)	80,218	102,994
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted-Average Exercise Price, Outstanding, beginning balance (in dollars per share)	$ 47.15	$ 41.08
Weighted-Average Exercise Price, Granted (in dollars per share)	0.00	66.32
Weighted-Average Exercise Price, Exercised (in dollars per share)	37.85	30.38
Weighted-Average Exercise Price, Outstanding, ending balance (in dollars per share)	$ 48.00	$ 45.53
Exercisable (shares)	24,943	23,276
Exercisable, Weighted average exercise price (US$ per share)	$ 40.38	$ 36.70
Proceeds from stock option exercises	$ 280	$ 38
Intrinsic value of stock options exercised	220	44
Stock-based compensation expense associated with stock options	54	$ 65
Unrecognized stock-based compensation expense associated with stock options	$ 328
Weighted average period (in years) in which the above amount is expected to be recognized	2 years 5 months