Stock-Based Compensation (Schedule Of Activity For Non-Vested Restricted Stock) (Details) - Restricted Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested at beginning of period, Shares	28,465	26,587	23,668
Granted, Shares	7,837	3,162	5,779
Vested, Shares	(6,492)	(1,284)	(2,570)
Forfeited, Shares	0	0	(290)
Non-vested at end of period, Shares	29,810	28,465	26,587
Non-vested at beginning of period, Weighted Average Fair Value at Grant Date	$ 77.93	$ 78.00	$ 79.02
Granted, Weighted Average Fair Value at Grant Date	105.06	89.10	84.90
Vested, Weighted Average Fair Value at Grant Date	85.58	106.92	103.65
Forfeited, Weighted Average Fair Value at Grant Date			78.12
Non-vested at end of period, Weighted Average Fair Value at Grant Date	$ 83.40	$ 77.93	$ 78.00