Consolidated Statement of Changes in Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Distributions in Excess of Net Income [Member]	Total Stockholders' Equity [Member]	Noncontrolling Interest Exchangeable Operating Partnership Units [Member]	Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships [Member]	Noncontrolling Interest [Member]
Beginning balance at Dec. 31, 2017	$ 6,733,054	$ 1,714	$ (18,307)	$ 7,873,104	$ (6,289)	$ (1,158,170)	$ 6,692,052	$ 10,907	$ 30,095	$ 41,002
Adjustment due to change inaccounting policy (note 1) at Dec. 31, 2017	30,903				12	30,889	30,901		2	2
Adjusted balance at Dec. 31, 2017	6,763,957	1,714	(18,307)	7,873,104	(6,277)	(1,127,281)	6,722,953	10,907	30,097	41,004
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	172,588					170,222	170,222	358	2,008	2,366
Other comprehensive income (loss)	21,161				20,343		20,343	43	775	818
Deferred compensation plan, net	(14)		(1,243)	1,229			(14)
Restricted stock issued, net of amortization	12,308	1		12,307			12,308
Common stock redeemed for taxes withheld for stock based compensation, net	(6,463)			(6,463)			(6,463)
Common stock repurchased and retired	(124,989)	(21)		(124,968)			(124,989)
Common stock issued under dividend reinvestment plan	996			996			996
Common stock issued, net of issuance costs	10			10			10
Distributions to partners	(3,457)								(3,457)	(3,457)
Cash dividends declared - common stock/unit	(283,854)					(283,272)	(283,272)	(582)		(582)
Ending Balance at Sep. 30, 2018	6,552,243	1,694	(19,550)	7,756,215	14,066	(1,240,331)	6,512,094	10,726	29,423	40,149
Beginning balance at Jun. 30, 2018	6,568,788	1,694	(19,268)	7,751,375	10,317	(1,216,018)	6,528,100	10,765	29,923	40,688
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	70,534					69,722	69,722	147	665	812
Other comprehensive income (loss)	3,889				3,749		3,749	8	132	140
Deferred compensation plan, net	(10)		(282)	272			(10)
Restricted stock issued, net of amortization	4,173			4,173			4,173
Common stock issued for stock based compensation, net of repurchases	77			77			77
Common stock issued under dividend reinvestment plan	318			318			318
Distributions to partners	(1,297)								(1,297)	(1,297)
Cash dividends declared - common stock/unit	(94,229)					(94,035)	(94,035)	(194)		(194)
Ending Balance at Sep. 30, 2018	6,552,243	1,694	(19,550)	7,756,215	14,066	(1,240,331)	6,512,094	10,726	29,423	40,149
Beginning balance at Dec. 31, 2018	6,450,168	1,679	(19,834)	7,672,517	(927)	(1,255,465)	6,397,970	10,666	41,532	52,198
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	202,127					199,139	199,139	456	2,532	2,988
Other comprehensive income (loss)	(16,053)				(14,877)		(14,877)	(36)	(1,140)	(1,176)
Deferred compensation plan, net	0		(3,024)	3,024
Restricted stock issued, net of amortization	12,127	2		12,125			12,127
Common stock redeemed for taxes withheld for stock based compensation, net	(5,857)			(5,857)			(5,857)
Common stock repurchased and retired	(32,777)	(5)		(32,772)			(32,777)
Common stock issued under dividend reinvestment plan	1,085			1,085			1,085
Contributions from partners	1,999								1,999	1,999
Issuance of exchangeable operating partnership units	25,869							25,869		25,869
Distributions to partners	(4,222)								(4,222)	(4,222)
Reallocation of limited partner's interest	0			(66)			(66)		66	66
Cash dividends declared - common stock/unit	(294,619)					(294,005)	(294,005)	(614)		(614)
Ending Balance at Sep. 30, 2019	6,339,847	1,676	(22,858)	7,650,056	(15,804)	(1,350,331)	6,262,739	36,341	40,767	77,108
Beginning balance at Jun. 30, 2019	6,352,848	1,676	(22,536)	7,645,065	(14,086)	(1,309,278)	6,300,841	10,528	41,479	52,007
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	57,944					56,965	56,965	157	822	979
Other comprehensive income (loss)	(2,005)				(1,718)		(1,718)	(8)	(279)	(287)
Deferred compensation plan, net	0		(322)	322
Restricted stock issued, net of amortization	4,224			4,224			4,224
Common stock issued for stock based compensation, net of repurchases	100			100			100
Common stock issued under dividend reinvestment plan	345			345			345
Contributions from partners	103								103	103
Issuance of exchangeable operating partnership units	25,869							25,869		25,869
Distributions to partners	(1,358)								(1,358)	(1,358)
Cash dividends declared - common stock/unit	(98,223)					(98,018)	(98,018)	(205)		(205)
Ending Balance at Sep. 30, 2019	$ 6,339,847	$ 1,676	$ (22,858)	$ 7,650,056	$ (15,804)	$ (1,350,331)	$ 6,262,739	$ 36,341	$ 40,767	$ 77,108