Condensed Consolidated Statements Of Equity (USD $) In Thousands		Total	Preferred Shares Of Beneficial Interest [Member]	Common Shares Of Beneficial Interest [Member]	Additional Paid-In Capital [Member]	Net Income Less Than Accumulated Dividends [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interests [Member]
Balance at Dec. 31, 2010		$ 1,980,257	$ 8	$ 3,630	$ 1,969,905	$ (151,780)	$ (21,774)	$ 180,268
Net Income		20,127				17,799		2,328
Shares issued under benefit plans		7,526		10	7,516
Dividends declared - common shares	[1]	(66,407)				(66,407)
Dividends declared - preferred shares	[2]	(16,426)				(16,426)
Distributions to noncontrolling interests		(7,259)						(7,259)
Contributions from noncontrolling interests		3,717						3,717
Other comprehensive income		948					948
Other, net		(897)			2,864	(1,312)		(2,449)
Balance at Jun. 30, 2011		1,921,586	8	3,640	1,980,285	(218,126)	(20,826)	176,605
Balance at Dec. 31, 2011		1,823,582	8	3,641	1,983,978	(304,504)	(27,743)	168,202
Net Income		55,399				52,616		2,783
Shares issued under benefit plans		8,276		12	8,264
Dividends declared - common shares	[1]	(70,278)				(70,278)
Dividends declared - preferred shares	[2]	(16,426)				(16,426)
Distributions to noncontrolling interests		(7,333)						(7,333)
Contributions from noncontrolling interests		2,123						2,123
Other comprehensive income		1,189					1,189
Other, net		737			1,109	(1,312)		940
Balance at Jun. 30, 2012		$ 1,797,269	$ 8	$ 3,653	$ 1,993,351	$ (339,904)	$ (26,554)	$ 166,715

[1] Common dividend per share was $0.58 and $0.55 for the six months ended June 30, 2012 and 2011, respectively.

[2] Series D, E and F preferred dividend per share was $25.31, $86.88 and $81.25, respectively, for both the six months ended June 30, 2012 and 2011.