Condensed Consolidated Statements Of Equity - USD ($) $ in Thousands	Total	Common shares of beneficial interest	Additional paid-in capital	Distributions in excess of net income	Treasury shares, at cost	Accumulated other comprehensive (loss)/income	Non-controlling interests
Cash distributions declared to equity holders per common share	$ 2.40
Beginning balance at Dec. 31, 2018	$ 3,385,104	$ 1,031	$ 4,154,763	$ (495,496)	$ (355,804)	$ 6,929	$ 73,681
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	128,045			124,609			3,436
Other comprehensive income (loss)	(13,367)					(13,367)
Common shares issued	328,374	34	328,340
Net share awards	17,219		10,565		6,654
Employee share purchase plan	1,807		1,213		594
Change in classification of deferred compensation plan	52,674		43,311	9,363
Conversion of operating partnership units	0		186				(186)
Cash distributions declared to equity holders	(242,299)			(238,091)			(4,208)
Other	224		44				180
Ending balance at Sep. 30, 2019	$ 3,657,781	1,065	4,538,422	(599,615)	(348,556)	(6,438)	72,903
Cash distributions declared to equity holders per common share	$ 0.80
Beginning balance at Jun. 30, 2019	$ 3,688,768	1,065	4,533,667	(563,834)	(348,480)	(6,795)	73,145
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	44,782			43,597			1,185
Other comprehensive income (loss)	357					357
Net share awards	4,549		4,625		(76)
Employee share purchase plan	57		57
Conversion of operating partnership units	0		71				(71)
Cash distributions declared to equity holders	(80,778)			(79,378)			(1,400)
Other	46		2				44
Ending balance at Sep. 30, 2019	$ 3,657,781	1,065	4,538,422	(599,615)	(348,556)	(6,438)	72,903
Cash distributions declared to equity holders per common share	$ 2.49
Beginning balance at Dec. 31, 2019	$ 3,701,724	1,069	4,566,731	(584,167)	(348,419)	(6,529)	73,039
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	98,198			94,718			3,480
Other comprehensive income (loss)	1,098					1,098
Common shares issued	0
Net share awards	16,914		10,729		6,185
Employee share purchase plan	1,082		679		403
Cash distributions declared to equity holders	(252,460)			(248,107)			(4,353)
Other	(549)	(1)	(326)				(222)
Ending balance at Sep. 30, 2020	$ 3,566,007	1,068	4,577,813	(737,556)	(341,831)	(5,431)	71,944
Cash distributions declared to equity holders per common share	$ 0.83
Beginning balance at Jun. 30, 2020	$ 3,610,567	1,068	4,574,387	(689,809)	(341,637)	(5,797)	72,355
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	36,220			34,957			1,263
Other comprehensive income (loss)	366					366
Net share awards	3,389		3,583		(194)
Employee share purchase plan	39		39
Cash distributions declared to equity holders	(84,156)			(82,704)			(1,452)
Other	(418)		(196)				(222)
Ending balance at Sep. 30, 2020	$ 3,566,007	$ 1,068	$ 4,577,813	$ (737,556)	$ (341,831)	$ (5,431)	$ 71,944