Equity Incentive Plans (Summary Of Outstanding Options) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Exercise price range, lower limit	$ 61.79		$ 51.64
Exercise price range, upper limit	$ 76.63	$ 61.79	$ 65.50
Options outstanding	257,606	285,986	516,305	950,214
Weighted avg. life remaining	5 years 6 months
Weighted avg. exercise price	$ 51.81	$ 51.93	$ 48.42	$ 42.48
Aggregate intrinsic value	$ 3,541
$ 19.02 - 19.99
Exercise price range, lower limit	$ 19.02
Exercise price range, upper limit	$ 19.99
Options outstanding	11,097
Weighted avg. life remaining	1 year 5 months
20.00 - 29.99 [Member]
Exercise price range, lower limit	$ 20.00
Exercise price range, upper limit	$ 29.99
Options outstanding	0
30.00 - 39.99 [Member]
Exercise price range, lower limit	$ 30.00
Exercise price range, upper limit	$ 39.99
Options outstanding	1,428
Weighted avg. life remaining	2 years
40.00 - 49.99 [Member]
Exercise price range, lower limit	$ 40.00
Exercise price range, upper limit	$ 49.99
Options outstanding	86,041
Weighted avg. life remaining	4 years 1 month
50.00 - 59.99 [Member]
Exercise price range, lower limit	$ 50.00
Exercise price range, upper limit	$ 59.99
Options outstanding	75,939
Weighted avg. life remaining	5 years 9 months
60.00 - 69.99 [Member]
Exercise price range, lower limit	$ 60.00
Exercise price range, upper limit	$ 61.79
Options outstanding	80,886
Weighted avg. life remaining	7 years 1 month
70.00 - 76.63 [Member]
Exercise price range, lower limit	$ 70.00
Exercise price range, upper limit	$ 76.63
Options outstanding	2,215
Weighted avg. life remaining	9 years 1 month