Condensed Consolidated Statements Of Equity (USD $) In Thousands, unless otherwise specified		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
Increase (Decrease) in Equity [Roll Forward]
Net Income (Loss)		(15,831)				(15,421)		(410)
Shares issued under benefit plans		8,747		11	8,736
Dividends declared - common shares	[1]	(99,638)				(99,638)
Dividends declared - preferred shares	[2]	(24,639)				(24,639)
Distributions to noncontrolling interests		(9,562)						(9,562)
Contributions from noncontrolling interests		3,717						3,717
Other comprehensive income		1,060					1,060
Other, net		(1,389)			3,477	(1,968)		(2,898)
Balance at Sep. 30, 2011		1,842,722	8	3,641	1,982,118	(293,446)	(20,714)	171,115
Balance at Dec. 31, 2011		1,823,582	8	3,641	1,983,978	(304,504)	(27,743)	168,202
Increase (Decrease) in Equity [Roll Forward]
Net Income (Loss)		97,446				92,889		4,557
Shares issued under benefit plans		11,503		17	11,486
Dividends declared - common shares	[1]	(105,466)				(105,466)
Dividends declared - preferred shares	[2]	(24,639)				(24,639)
Distributions to noncontrolling interests		(10,119)						(10,119)
Contributions from noncontrolling interests		2,123						2,123
Other comprehensive income		1,804					1,804
Other, net		617			1,766	(1,968)		819
Balance at Sep. 30, 2012		$ 1,796,851	$ 8	$ 3,658	$ 1,997,230	$ (343,688)	$ (25,939)	$ 165,582

[1] Common dividend per share was $0.870 and $0.825 for the nine months ended September 30, 2012 and 2011, respectively.

[2] Series D, E and F preferred dividend per share was $37.97, $130.31 and $121.88, respectively, for both the nine months ended September 30, 2012 and 2011.