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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Income from continuing operations	$ 39,390	$ 39,285	$ 108,208	$ 104,437
Less: Preferred share dividends	(136)	(136)	(406)	(406)
Less: Income from continuing operations attributable to noncontrolling interests	(1,268)	(1,012)	(3,780)	(3,141)
Less: Earnings allocated to unvested shares	(278)	(221)	(659)	(638)
Income from continuing operations available for common shareholders	37,708	37,916	103,363	100,252
Results from discontinued operations attributable to the Trust	23,976	371	24,803	1,077
Gain on sale of real estate	0	0	4,994	11,860
Net income available for common shareholders, basic and diluted	61,684	38,287	133,160	113,189
Weighted average common shares outstanding-basic	65,504	64,014	65,118	63,711
Stock options	143	188	153	180
Weighted average common shares outstanding-diluted	65,647	64,202	65,271	63,891
Continuing operations	$ 0.57	$ 0.59	$ 1.58	$ 1.57
Discontinued Operations	$ 0.37	$ 0.01	$ 0.38	$ 0.02
Gain on Sale of Real Estate per Basic Share	$ 0.00	$ 0.00	$ 0.08	$ 0.19
Earnings Per Share, Basic, Total	$ 0.94	$ 0.60	$ 2.04	$ 1.78
Continuing operations	$ 0.57	$ 0.59	$ 1.58	$ 1.56
Discontinued Operations	$ 0.37	$ 0.01	$ 0.38	$ 0.02
Gain on sale of real estate	$ 0.00	$ 0.00	$ 0.08	$ 0.19
Earnings Per Share, Diluted, Total	$ 0.94	$ 0.60	$ 2.04	$ 1.77
Income from continuing operations attributable to the Trust	$ 38,122	$ 38,273	$ 104,428	$ 101,296