Consolidated Statements Of Equity - USD ($) $ in Thousands	Total	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, 2016	$ 1,716,896	$ 3,885	$ 1,718,101	$ (177,647)	$ (9,161)	$ 181,718
Increase (Decrease) in Equity [Roll Forward]
Net Income	350,715			335,274		15,441
Shares issued under benefit plans, net	8,828	12	8,816
Change in classification of deferred compensation plan	45,377		45,377
Change in redemption value of deferred compensation plan	(619)			(619)
Dividends paid – common shares (dollars per share for each period)	(294,073)			(294,073)
Distributions to noncontrolling interests	(19,342)					(19,342)
Other comprehensive income (loss)	2,991				2,991
Other, net	(931)		(228)			(703)
Ending balance at Dec. 31, 2017	1,809,842	3,897	1,772,066	(137,065)	(6,170)	177,114
Increase (Decrease) in Equity [Roll Forward]
Net Income	345,343			327,601		17,742
Shares issued under benefit plans, net	13,487	16	13,471
Dividends paid – common shares (dollars per share for each period)	(382,464)			(382,464)
Distributions to noncontrolling interests	(19,155)					(19,155)
Other comprehensive income (loss)	(2,838)				(2,838)
Other, net	(373)					(373)
Shares repurchased and cancelled	(18,564)	(20)	(18,544)
Contributions from noncontrolling interests	1,465					1,465
Ending balance at Dec. 31, 2018	1,750,699	3,893	1,766,993	(186,431)	(10,549)	176,793
Increase (Decrease) in Equity [Roll Forward]
Net Income	322,575			315,435		7,140
Shares issued under benefit plans, net	11,058	12	11,046
Dividends paid – common shares (dollars per share for each period)	(203,297)			(203,297)
Distributions to noncontrolling interests	(6,782)					(6,782)
Other comprehensive income (loss)	(734)				(734)
Other, net	2,315		1,947			368
Contributions from noncontrolling interests	326					326
Ending balance at Dec. 31, 2019	$ 1,876,160	$ 3,905	$ 1,779,986	$ (74,293)	$ (11,283)	$ 177,845