Earnings Per Share (Schedule Of Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share [Abstract]
Income from continuing operations	$ 33,532	$ 30,740	$ 99,388	$ 91,715
Less: Dividends on preferred shares	(136)	(136)	(406)	(406)
Less: Income from continuing operations attributable to noncontrolling interests	(1,249)	(1,370)	(3,941)	(3,958)
Less: Earnings allocated to unvested shares	(207)	(136)	(509)	(404)
Income from continuing operations available for common shareholders	31,940	29,098	94,532	86,947
Results from discontinued operations attributable to the Trust	14,770	270	17,549	1,807
Gain on sale of real estate				410
Net income available for common shareholders, basic and diluted	46,710	29,368	112,081	89,164
Weighted average common shares outstanding-basic	62,818	61,215	62,172	61,158
Stock options	172	144	169	139
Weighted average common shares outstanding-diluted	62,990	61,359	62,341	61,297
Continuing operations	$ 0.51	$ 0.48	$ 1.52	$ 1.42
Discontinued operations	$ 0.23		$ 0.28	$ 0.03
Gain on sale of real estate				$ 0.01
Earnings Per Share, Basic, Total	$ 0.74	$ 0.48	$ 1.80	$ 1.46
Continuing operations	$ 0.51	$ 0.48	$ 1.52	$ 1.41
Discontinued operations	$ 0.23		$ 0.28	$ 0.03
Gain on sale of real estate				$ 0.01
Earnings Per Share, Diluted, Total	$ 0.74	$ 0.48	$ 1.80	$ 1.45
Income from continuing operations attributable to the Trust	$ 32,283	$ 29,370	$ 95,447	$ 87,757