Employee Benefit Plans (Summary Of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Exercised (in shares)	(16,639)	(21,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Proceeds from stock option exercises	$ 597	$ 705
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options Outstanding, beginning balance (in shares)	86,613	95,015
Options, Granted (in shares)	17,631	24,348
Options, Exercised (in shares)	(16,639)	(21,000)
Options Outstanding, ending balance (in shares)	87,605	98,363
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)	$ 41.08	$ 38.38
Weighted-Average Exercise Price, Granted (in dollars per share)	66.32	43.73
Weighted-Average Exercise Price, Exercised (in dollars per share)	35.91	33.57
Weighted-Average Exercise Price, Outstanding, ending balance (in dollars per share)	$ 47.15	$ 40.76
Exercisable (shares)	7,887	14,750
Exercisable, Weighted average exercise price (US$ per share)	$ 37.37	$ 36.53
Proceeds from stock option exercises	$ 597	$ 705
Intrinsic value of stock options exercised	481	317
Stock-based compensation expense associated with stock options	186	$ 180
Unrecognized stock-based compensation expense associated with stock options	$ 442
Weighted average period (in years) in which the above amount is expected to be recognized	2 years 8 months