Share-based Compensation and Non-Qualified Deferred Compensation Plan (Summary Of Share Incentive Plans) (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Options, Number At December 31, 2017 | shares	68,978
Granted, Options Outstanding | shares	9,994
Exercised/Vested, Options Outstanding | shares	(26,114)
Forfeited, Options Outstanding | shares	0
Outstanding Options, Number At March 31, 2018 | shares	52,858
Options outstanding at December 31, 2017, Weighted Average Exercise/Grant Price | $ / shares	$ 61.15
Granted, Weighted Average Exercise/Grant Price | $ / shares	78.55
Exercised/Vested, Weighted Average Exercise/Grant Price | $ / shares	30.06
Forfeited, Weighted Average Exercise/Grant Price | $ / shares	0.00
Options outstanding at March 31, 2018, Weighted Average Exercise/Grant Price | $ / shares	$ 79.79	[1]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested share awards outstanding at December 31, 2017, Share Awards Outstanding | shares	499,898
Granted, Share Awards Outstanding | shares	211,417
Exercised/Vested, Share Awards Outstanding | shares	(298,419)
Forfeited, Share Awards Outstanding | shares	(12,650)
Nonvested share awards outstanding at March 31, 2018, Share Awards Outstanding | shares	400,246
Nonvested share awards outstanding at December 31, 2017, Weighted Average Exercise/Grant Price | $ / shares	$ 75.80
Granted, Weighted Average Exercise/Grant Price | $ / shares	82.65
Exercised/Vested, Weighted Average Exercise/Grant Price | $ / shares	75.22
Forfeited, Weighted Average Exercise/Grant Price | $ / shares	79.16
Nonvested share awards outstanding at March 31, 2018, Weighted Average Exercise/Grant Price | $ / shares	$ 79.74

[1] The aggregate intrinsic value of options outstanding and exercisable at March 31, 2018 was $0.2 million. The aggregate intrinsic value was calculated as the excess, if any, between our closing share price of $84.18 per share on March 31, 2018 and the strike price of the underlying award.