Condensed Consolidated Statements of Equity (Unaudited) - 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, 2014		$ 1,638,943	$ 2	$ 3,700	$ 1,706,880	$ (212,960)	$ (12,436)	$ 153,757
Increase (Decrease) in Equity [Roll Forward]
Net Income		49,222				47,647		1,575
Issuance of common shares, net		29,036		24	29,012
Shares issued under benefit plans, net		5,556		9	5,547
Shares issued in exchange for noncontrolling interests		0			111			(111)
Dividends paid - common shares	[1]	(42,476)				(42,476)
Dividends paid - preferred shares	[2]	(2,438)				(2,438)
Distributions to noncontrolling interests		(1,660)						(1,660)
Other comprehensive loss		(523)					(523)
Other, net		(132)			254	(272)		(114)
Ending Balance at Mar. 31, 2015		1,675,528	2	3,733	1,741,804	(210,499)	(12,959)	153,447
Beginning 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		108,667				107,074		1,593
Issuance of common shares, net		17,880		15	17,865
Shares issued under benefit plans, net		2,215		26	2,189
Dividends paid - common shares	[1]	(45,378)				(45,378)
Distributions to noncontrolling interests		(2,139)						(2,139)
Other comprehensive loss		(3,665)					(3,665)
Ending Balance at Mar. 31, 2016		$ 1,622,590	$ 0	$ 3,785	$ 1,636,296	$ (161,184)	$ (11,309)	$ 155,002

[1] Common dividend per share was $.365 and $.345 for the three months ended March 31, 2016 and 2015, respectively.

[2] Series F preferred dividend per share was $40.63 for the three months ended March 31, 2015