Share-based Compensation and Non-Qualified Deferred Compensation Plan (Summary Of Share Options Outstanding And Exercisable) (Details) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Outstanding and Exercisable Options, Number | shares	80,342	[1]
Aggregate intrinsic value of outstanding options | $	$ 2.3
Aggregate Intrinsic Value of Exercisable Options | $	$ 2.3
Closing share price per share for calculation of aggregate intrinsic values	$ 91.45
Options outstanding at September 30, 2017, Weighted Average Exercise/Grant Price	63.13	[1]
Exercise Price $30.06 Member [Domain]
Range of exercise prices, minimum	30.06
Range of exercise prices, maximum	$ 30.06
Outstanding and Exercisable Options, Number | shares	26,114	[1]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 30.06	[1]
Exercise Price $75.17 Member [Domain]
Range of exercise prices, minimum	75.17
Range of exercise prices, maximum	$ 75.17
Outstanding and Exercisable Options, Number | shares	26,752	[1]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 75.17	[1]
Range Of Exercise Prices $80.89 to $85.05 Member [Domain] [Domain]
Range of exercise prices, minimum	80.89
Range of exercise prices, maximum	$ 85.05
Outstanding and Exercisable Options, Number | shares	27,476	[1]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 82.84	[1]

[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.