Earnings Per Share (Schedule Of Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share [Abstract]
Income from continuing operations	$ 33,596	$ 33,893	$ 65,858	$ 65,856
Less: Preferred share dividends	(135)	(135)	(271)	(271)
Less: Income from continuing operations attributable to noncontrolling interests	(993)	(1,504)	(2,129)	(2,692)
Less: Earnings allocated to unvested shares	(208)	(125)	(416)	(316)
Income from continuing operations available for common shareholders	32,260	32,129	63,042	62,577
Results from discontinued operations attributable to the Trust	0	2,368	0	2,779
Gain On Sale Of Real Estate in Real Estate Partnership	0	0	11,860	0
Net income available for common shareholders, basic and diluted	32,260	34,497	74,902	65,356
Weighted average common shares outstanding-basic	63,700	62,214	63,556	61,844
Stock options	180	177	176	168
Weighted average common shares outstanding-diluted	63,880	62,391	63,732	62,012
Continuing operations	$ 0.51	$ 0.51	$ 0.99	$ 1.01
Discontinued operations	$ 0.00	$ 0.04	$ 0.00	$ 0.05
Gain on sale of real estate	$ 0.00	$ 0.00	$ 0.19	$ 0.00
Earnings Per Share, Basic, Total	$ 0.51	$ 0.55	$ 1.18	$ 1.06
Continuing operations	$ 0.51	$ 0.51	$ 0.99	$ 1.00
Discontinued operations	$ 0.00	$ 0.04	$ 0.00	$ 0.05
Gain on sale of real estate	$ 0.00	$ 0.00	$ 0.19	$ 0.00
Earnings Per Share, Diluted, Total	$ 0.51	$ 0.55	$ 1.18	$ 1.05
Income from continuing operations attributable to the Trust	$ 32,603	$ 32,389	$ 63,729	$ 63,164