Consolidated Statements Of Equity - USD ($) $ in Thousands	Total	Preferred Shares of Beneficial Interest	Common Shares of Beneficial Interest	Additional Paid-In Capital	Net Income Less Than Accumulated Dividends	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Beginning 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, net	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 loss	(8,234)					(8,234)
Other, net	(597)			755	(1,088)		(264)
Ending 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
Shares issued under benefit plans, net	8,999		10	8,989
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 loss	4,792					4,792
Other, net	(486)			279	43		(808)
Redemption of preferred shares	(150,000)	(2)		(140,311)	(9,687)
Issuance of common shares, net	40,328		34	40,294
Shares issued in exchange for noncontrolling interests	0			111			(111)
Ending balance at Dec. 31, 2015	1,545,010	0	3,744	1,616,242	(222,880)	(7,644)	155,548
Increase (Decrease) in Equity [Roll Forward]
Net income	276,831				238,933		37,898
Shares issued under benefit plans, net	7,466		36	7,430
Dividends paid – common shares	(185,100)				(185,100)
Distributions to noncontrolling interests	(9,563)						(9,563)
Acquisition of noncontrolling interests	(2,869)			(730)			(2,139)
Other comprehensive loss	(1,517)					(1,517)
Other, net	(26)						(26)
Issuance of common shares, net	131,422		105	131,317
Change in redemption value of deferred compensation plan	(39,977)			(39,977)
Diversification of share awards within deferred compensation plan	(8,600)				(8,600)
Diversification of share awards within deferred compensation plan	3,819			3,819
Ending balance at Dec. 31, 2016	$ 1,716,896	$ 0	$ 3,885	$ 1,718,101	$ (177,647)	$ (9,161)	$ 181,718