Stock-Based Compensation (Schedule Of Stock Option Plans Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Options outstanding, December 31, 2016	91,000
Options exercised (in shares)	(28,000)
Options forfeited and expired (in shares)	0
Options outstanding, December 31, 2017	63,000	91,000
Options exercisable at end of year (in shares)	63,000
Weighted average exercise price
Exercised	$ 66.08
Options outstanding, December 31, 2017	62.86	$ 63.84
Options exercisable at end of year (usd per share)	$ 62.86
Stock Options Plans
Shares
Options outstanding, December 31, 2016	91,000	169,000	298,000
Options exercised (in shares)	(28,000)	(78,000)	(66,000)
Options forfeited and expired (in shares)	0	0	(63,000)
Options outstanding, December 31, 2017	63,000	91,000	169,000
Options exercisable at end of year (in shares)	63,000	90,000	164,000
Minimum | Stock Options Plans
Weighted average exercise price
Exercised	$ 57.34	$ 28.37	$ 28.37
Options forfeited and expired during the year (usd per share)	28.37	0.00	28.37
Options outstanding, December 31, 2017	57.34	57.34	28.37
Options exercisable at end of year (usd per share)	57.34	57.34	28.37
Maximum | Stock Options Plans
Weighted average exercise price
Exercised	66.14	93.65	93.65
Options forfeited and expired during the year (usd per share)	93.65	0.00	88.33
Options outstanding, December 31, 2017	66.14	66.14	93.65
Options exercisable at end of year (usd per share)	$ 66.14	$ 66.14	$ 93.65