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, 2009		$ 2,106,656	$ 8	$ 3,615	$ 1,958,975	$ (37,350)	$ (23,958)	$ 205,366
Increase (Decrease) in Equity [Roll Forward]
Net income		51,238				46,206		5,032
Shares issued in exchange for noncontrolling interests		0		1	745			(746)
Shares issued under benefit plans		8,019		14	8,005
Dividends declared - common shares	[1]	(125,160)				(125,160)
Dividends declared - preferred shares	[2]	(32,852)				(32,852)
Distributions to noncontrolling interests		(13,014)						(13,014)
Contributions from noncontrolling interests		2,686						2,686
Consolidation of joint ventures		(18,573)						(18,573)
Other comprehensive income (loss)		2,184					2,184
Other, net		(927)			2,180	(2,624)		(483)
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		16,739				15,621		1,118
Shares issued in exchange for noncontrolling interests								0
Shares issued under benefit plans		9,909		11	9,898
Dividends declared - common shares	[1]	(132,869)				(132,869)
Dividends declared - preferred shares	[2]	(32,852)				(32,852)
Distributions to noncontrolling interests		(23,560)						(23,560)
Contributions from noncontrolling interests		13,666						13,666
Other comprehensive income (loss)		(5,969)					(5,969)
Other, net		(1,739)			4,175	(2,624)		(3,290)
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		152,421				146,640		5,781
Redemption of Series E preferred shares		(72,500)	(1)		(69,999)	(2,500)
Shares issued in exchange for noncontrolling interests								0
Shares issued under benefit plans		16,590		22	16,568
Dividends declared - common shares	[1]	(140,686)				(140,686)
Dividends declared - preferred shares	[2]	(32,516)				(32,516)
Distributions to noncontrolling interests		(12,770)						(12,770)
Contributions from noncontrolling interests		2,123						2,123
Other comprehensive income (loss)		3,000					3,000
Other, net		911			3,636	(2,414)		(311)
Balance at Dec. 31, 2012		$ 1,740,155	$ 7	$ 3,663	$ 1,934,183	$ (335,980)	$ (24,743)	$ 163,025

[1] Common dividend per share was $1.16, $1.10 and $1.04 for the year ended December 31, 2012, 2011 and 2010, respectively.

[2] Series D and F preferred dividend per share was $50.63 and $162.50 for the year ended December 31, 2012, 2011 and 2010, respectively. Series E preferred dividend per share was $162.16 for the year ended December 31, 2012, and $173.75 for the year ended December 31, 2011 and 2010.