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, 2012	$ 1,740,155	$ 7	$ 3,663	$ 1,934,183	$ (335,980)	$ (24,743)	$ 163,025
Increase (Decrease) in Equity [Roll Forward]
Net income	265,156				220,262		44,894
Redemption of preferred shares	(275,000)	(5)		(257,051)	(17,944)
Shares issued under benefit plans	13,608		20	13,588
Dividends paid – common shares	(148,702)				(148,702)
Dividends paid – preferred shares	(17,198)				(17,198)
Distributions to noncontrolling interests	(20,151)						(20,151)
Contributions from noncontrolling interests	106,613						106,613
Acquisition of noncontrolling interests	0			(16,177)			16,177
Other comprehensive income (loss)	20,541					20,541
Other, net	2,956			4,686	(975)		(755)
Balance at Dec. 31, 2013	1,687,978	2	3,683	1,679,229	(300,537)	(4,202)	309,803
Increase (Decrease) in Equity [Roll Forward]
Net income	307,579				288,008		19,571
Shares issued under benefit plans	15,898		17	15,881
Dividends paid – common shares	(189,591)				(189,591)
Dividends paid – preferred shares	(9,752)				(9,752)
Distributions to noncontrolling interests	(21,055)						(21,055)
Contributions from noncontrolling interests	980						980
Acquisition of noncontrolling interests	0			11,015			(11,015)
Disposition of noncontrolling interests	(144,263)						(144,263)
Other comprehensive income (loss)	(8,234)					(8,234)
Other, net	(597)			755	(1,088)		(264)
Balance at Dec. 31, 2014	1,638,943	2	3,700	1,706,880	(212,960)	(12,436)	153,757
Increase (Decrease) in Equity [Roll Forward]
Net income	181,222				174,352		6,870
Redemption of preferred shares	(150,000)	(2)		(140,311)	(9,687)
Issuance of common shares, net	40,328		34	40,294
Shares issued under benefit plans	8,999		10	8,989
Shares issued in exchange for noncontrolling interests	0			111			(111)
Dividends paid – common shares	(170,755)				(170,755)
Dividends paid – preferred shares	(3,873)				(3,873)
Distributions to noncontrolling interests	(5,478)						(5,478)
Contributions from noncontrolling interests	1,318						1,318
Other comprehensive income (loss)	4,792					$ 4,792
Other, net	(486)			279	43		(808)
Balance at Dec. 31, 2015	$ 1,545,010	$ 0	$ 3,744	$ 1,616,242	$ (222,880)	$ (7,644)	$ 155,548