Share-based Compensation and Non-Qualified Deferred Compensation Plan (Summary Of Share Options Outstanding And Exercisable) (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Outstanding and Exercisable Options, Number | shares	52,858	[1]
Aggregate intrinsic value of outstanding options | $	$ 0.2
Aggregate Intrinsic Value of Exercisable Options | $	$ 0.2
Closing share price per share for calculation of aggregate intrinsic values	$ 84.18
Options outstanding at March 31, 2018, Weighted Average Exercise/Grant Price	79.79	[1]
Exercise Price $75.17 [Member]
Range of exercise prices, minimum	75.17
Range of exercise prices, maximum	$ 75.17
Outstanding and Exercisable Options, Number | shares	15,388	[1]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 75.17	[1]
Exercise Price $78.55 [Member]
Range of exercise prices, minimum	78.55
Range of exercise prices, maximum	$ 78.55
Outstanding and Exercisable Options, Number | shares	9,994	[1]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 78.55	[1]
Range Of Exercise Prices $80.89 to $85.05 [Member]
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 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.