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, 2011		$ 1,823,582	$ 8	$ 3,641	$ 1,983,978	$ (304,504)	$ (27,743)	$ 168,202
Increase (Decrease) in Equity [Roll Forward]
Net Income		22,638				21,197		1,441
Shares issued under benefit plans		4,715		8	4,707
Dividends declared - common shares	[1]	(35,120)				(35,120)
Dividends declared - preferred shares	[2]	(8,213)				(8,213)
Distributions to noncontrolling interests		(3,756)						(3,756)
Other comprehensive income (loss)		675					675
Other, net		(262)			513	(656)		(119)
Balance at Mar. 31, 2012		1,804,259	8	3,649	1,989,198	(327,296)	(27,068)	165,768
Balance at Dec. 31, 2012		1,740,155	7	3,663	1,934,183	(335,980)	(24,743)	163,025
Increase (Decrease) in Equity [Roll Forward]
Net Income		44,817				43,350		1,467
Redemption of Series D preferred shares		(75,000)	(3)		(72,755)	(2,242)
Shares issued under benefit plans		6,408		8	6,400
Dividends declared - common shares	[1]	(37,127)				(37,127)
Dividends declared - preferred shares	[2]	(6,995)				(6,995)
Distributions to noncontrolling interests		(3,858)						(3,858)
Other comprehensive income (loss)		(1,086)					(1,086)
Other, net		426			387	(445)		484
Balance at Mar. 31, 2013		$ 1,667,740	$ 4	$ 3,671	$ 1,868,215	$ (339,439)	$ (25,829)	$ 161,118

[1] Common dividend per share was $.305 and $.290 for the three months ended March 31, 2013 and 2012, respectively.

[2] Series D preferred dividend per share was $13.08 and $12.66 for the three months ended March 31, 2013 and 2012, respectively. Series E preferred dividend per share was $43.44 for the three months ended March 31, 2012. Series F preferred dividend per share was $40.63 for both the three months ended March 31, 2013 and 2012.