Share-based Compensation and Non-Qualified Deferred Compensation Plan (Summary Of Share Incentive Plans) (Details)	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding Options, Number At December 31, 2016 | shares	105,066
Granted, Options Outstanding | shares	14,622
Exercised/Vested, Options Outstanding | shares	(39,346)
Forfeited, Options Outstanding | shares	0
Outstanding Options, Number At September 30, 2017 | shares	80,342
Options outstanding at December 31, 2016, Weighted Average Exercise/Grant Price | $ / shares	$ 48.27
Granted, Weighted Average Exercise/Grant Price | $ / shares	80.89
Exercised/Vested, Weighted Average Exercise/Grant Price | $ / shares	30.06
Forfeited, Weighted Average Exercise/Grant Price | $ / shares	0.00
Options outstanding at September 30, 2017, Weighted Average Exercise/Grant Price | $ / shares	$ 63.13	[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, 2016, Share Awards Outstanding | shares	604,487
Granted, Share Awards Outstanding | shares	225,496
Exercised/Vested, Share Awards Outstanding | shares	(319,823)
Forfeited, Share Awards Outstanding | shares	(8,876)
Nonvested share awards outstanding at September 30, 2017, Share Awards Outstanding | shares	501,284
Nonvested share awards outstanding at December 31, 2016, Weighted Average Exercise/Grant Price | $ / shares	$ 71.03
Granted, Weighted Average Exercise/Grant Price | $ / shares	83.41
Exercised/Vested, Weighted Average Exercise/Grant Price | $ / shares	72.26
Forfeited, Weighted Average Exercise/Grant Price | $ / shares	74.73
Nonvested share awards outstanding at September 30, 2017, Weighted Average Exercise/Grant Price | $ / shares	$ 75.77

[1] The aggregate intrinsic value of options outstanding and exercisable at September 30, 2017 was $2.3 million. The aggregate intrinsic value was calculated as the excess, if any, between our closing share price of $91.45 per share on September 30, 2017 and the strike price of the underlying award.