Employee Benefit Plans (Summary Of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Exercised (in shares)	(25,147)	(16,639)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Proceeds from stock option exercises	$ 968	$ 597
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)	(25,147)	(16,639)
Options Outstanding, ending balance (in shares)	62,458	87,605
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)	38.51	35.91
Weighted-Average Exercise Price, Outstanding, ending balance (in dollars per share)	$ 50.62	$ 47.15
Exercisable (shares)	7,183	7,887
Exercisable, Weighted average exercise price (US$ per share)	$ 44.32	$ 37.37
Proceeds from stock option exercises	$ 968	$ 597
Intrinsic value of stock options exercised	824	481
Stock-based compensation expense associated with stock options	95	$ 125
Unrecognized stock-based compensation expense associated with stock options	$ 287
Weighted average period (in years) in which the above amount is expected to be recognized	2 years 3 months