Earnings Per Share (Schedule Of Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Abstract]
Income from continuing operations	$ 39,656	$ 33,532	$ 105,514	$ 99,388
Less: Preferred share dividends	(136)	(136)	(406)	(406)
Less: Income from continuing operations attributable to noncontrolling interests	(1,012)	(1,249)	(3,141)	(3,941)
Less: Earnings allocated to unvested shares	(221)	(207)	(638)	(509)
Income from continuing operations available for common shareholders	38,287	31,940	101,329	94,532
Results from discontinued operations attributable to the Trust	0	14,770	0	17,549
Gain On Sale Of Real Estate in Real Estate Partnership	0	0	11,860	0
Net income available for common shareholders, basic and diluted	38,287	46,710	113,189	112,081
Weighted average common shares outstanding-basic	64,014	62,818	63,711	62,172
Stock options	188	172	180	169
Weighted average common shares outstanding-diluted	64,202	62,990	63,891	62,341
Continuing operations	$ 0.60	$ 0.51	$ 1.59	$ 1.52
Discontinued operations	$ 0.00	$ 0.23	$ 0.00	$ 0.28
Gain on sale of real estate	$ 0.00	$ 0.00	$ 0.19	$ 0.00
Earnings Per Share, Basic, Total	$ 0.60	$ 0.74	$ 1.78	$ 1.80
Continuing operations	$ 0.60	$ 0.51	$ 1.58	$ 1.52
Discontinued operations	$ 0.00	$ 0.23	$ 0.00	$ 0.28
Gain on sale of real estate	$ 0.00	$ 0.00	$ 0.19	$ 0.00
Earnings Per Share, Diluted, Total	$ 0.60	$ 0.74	$ 1.77	$ 1.80
Income from continuing operations attributable to the Trust	$ 38,644	$ 32,283	$ 102,373	$ 95,447