Interim Financial Statements (Anti-Dilutive Securities Of Common Shares Of Beneficial Interest) (Details) In Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities	5,664		5,202		5,412		5,220
Share Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities	3,163	[1]	3,553	[1]	2,846	[1]	3,553	[1]
Operating Partnership Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities	1,607		1,649		1,626		1,667
Share Options And Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dilutive securities	894				940

[1] Exclusion results as exercise prices were greater than the average market price for each respective period.