Equity Incentive Plans (Summary Of Share Option Activity) (Details) (USD $)	3 Months Ended	9 Months Ended			9 Months Ended			9 Months Ended			9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Minimum [Member]	Sep. 30, 2013 Minimum [Member]	Dec. 31, 2013 Minimum [Member]	Sep. 30, 2014 Maximum [Member]	Sep. 30, 2013 Maximum [Member]	Dec. 31, 2013 Maximum [Member]	Sep. 30, 2014 Share Options [Member]	Sep. 30, 2013 Share Options [Member]	Sep. 30, 2013 Share Options [Member] Minimum [Member]	Sep. 30, 2013 Share Options [Member] Maximum [Member]	Sep. 30, 2014 2007 Equity Incentive Plan [Member]	May 09, 2007 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)															1,308,186
Maximum term of options granted (in years)		10 years
Share based compensation, future vesting period minimum (in years)		4 years			3 years			4 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		840,665
Number of Shares, Exercised		(28,434)
Number of Shares, Granted		172,178
Number of Shares, Outstanding at End of Period	981,032	981,032
Option Price Per Share, Outstanding at Beginning of Period					$ 18.18		$ 18.18	$ 65.50		$ 65.50
Option Price Per Share, Exercised					$ 32.50			$ 52.72
Option Price Per Share, Granted					$ 51.64			$ 51.64
Option Price Per Share, Outstanding at End of Period					$ 18.18		$ 18.18	$ 65.50		$ 65.50
Average Exercise Price, Outstanding at Beginning of Period	$ 42.69	$ 42.69		$ 40.85
Average Exercise Price, Exercised		$ 42.03
Average Exercise Price, Granted		$ 51.64
Average Exercise Price, Outstanding at End of Period	$ 42.69	$ 42.69		$ 40.85
Weighted average fair value of options granted		$ 13.87	$ 12.35
Intrinsic value of stock options exercised		$ 300,000	$ 2,900,000
Repurchase of treasury stock (in shares)		22,652
Repurchase of treasury stock, value		1,200,000
Share based compensation expenses recognized in future periods		3,000,000
Stock-option expense											$ 1,100,000	$ 647,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Minimum											2.20%	1.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate											6.40%		5.40%	6.50%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate											50.30%	50.70%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Forfeiture Rate											0.28%	0.23%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term											6 years	6 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period			3,377
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period, Price Per Share						$ 45.20			$ 51.64
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price			$ 48.65