Equity Incentive Plans (Summary Of Share Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	May. 09, 2007
Maximum term of options granted (in years)			10 years
Share based compensation, future vesting period minimum (in years)			4 years
Exercisable rate for employees options, per year			25.00%
Length of period subsequent to grant date options not exercisable for non-employee trustees (in years)			1 year
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares, Outstanding at Beginning of Period			950,214
Number of Shares, Exercised			(438,236)
Number of Shares, Granted			121,546
Number of Shares, Outstanding at End of Period	554,469		554,469
Average Exercise Price, Outstanding at Beginning of Period	$ 47.90		$ 47.90		$ 42.48
Average Exercise Price, Exercised			37.12
Average Exercise Price, Granted			61.79
Average Exercise Price, Outstanding at End of Period	$ 47.90		47.90		42.48
Weighted average fair value of options granted			$ 16.35	$ 13.87
Intrinsic value of stock options exercised			$ 6,700	$ 300
Repurchase of treasury stock (in shares)			371,343
Repurchase of treasury stock, value			$ 19,500
Share based compensation expenses recognized in future periods			2,200
Retirement severance expense	$ 0	$ 0	$ 18,578	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period			79,055
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price			$ 63.88
Minimum [Member]
Share based compensation, future vesting period minimum (in years)			3 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Option Price Per Share, Outstanding at Beginning of Period	$ 19.02		$ 19.02		18.18
Option Price Per Share, Exercised			18.18
Option Price Per Share, Granted			61.79
Option Price Per Share, Outstanding at End of Period	19.02		19.02		18.18
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period, Price Per Share			$ 45.20
Maximum [Member]
Share based compensation, future vesting period minimum (in years)			4 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Option Price Per Share, Outstanding at Beginning of Period	65.50		$ 65.50		65.50
Option Price Per Share, Exercised			61.53
Option Price Per Share, Granted			61.79
Option Price Per Share, Outstanding at End of Period	$ 65.50		65.50		$ 65.50
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period, Price Per Share			$ 65.50
Share Options [Member]
Share based compensation, future vesting period minimum (in years)			4 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
stock option expense including severance costs			$ 2,200
Stock-option expense			$ 830	$ 1,100
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Minimum			1.90%	2.20%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate			5.90%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate			48.00%	50.30%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Forfeiture Rate			0.78%	0.28%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term			6 years	6 years
Share Options [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate				6.40%
2007 Equity Incentive Plan [Member]
Common shares, options to purchase common shares and restricted share units, expected to granted (in shares)						3,650,000
Number of shares available for grant (in shares)	1,066,138		1,066,138