Consolidated Statement of Changes in Partner Capital Statement - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Adjusted balance			$ 6,763,957
Net income	$ 47,317	$ 243,258	252,325
Other comprehensive income
Amounts reclassified from accumulated other comprehensive income	11,262	3,269	5,342
Contributions from partners	606	2,151	13,000
Exchangeable operating partnership units issued for acquisition of real estate	1,275	25,870
Distributions to partners	(4,888)	(5,518)	(4,526)
Restricted stock issued, net of amortization	14,248	16,254	16,745
Total Stockholders' Equity [Member]
Adjusted balance			6,722,953
Net income	44,889	239,430	249,127
Other comprehensive income
Amounts reclassified from accumulated other comprehensive income	10,961	3,318	5,314
Reallocation of limited partners' interest		(66)
Restricted stock issued, net of amortization	14,248	16,254	16,745
Partnership Interest [Member]
Beginning Balance	6,289,961	6,450,168	6,733,054
Adjustment due to change in accounting policy (note 1)			30,903
Adjusted balance			6,763,957
Net income	47,317	243,258	252,325
Other comprehensive income
Other comprehensive income before reclassifications	(18,867)	(15,270)	307
Amounts reclassified from accumulated other comprehensive income	11,262	3,269	5,342
Deferred compensation plan, net			(13)
Contributions from partners	606	2,151	13,000
Exchangeable operating partnership units issued for acquisition of real estate	1,275	25,870
Distributions to partners	(409,343)	(398,596)	(382,614)
Reallocation of limited partners' interest		0
Restricted stock issued, net of amortization	14,248	16,254	16,745
Common units issued as a result of common stock issued by Parent Company, net of issuance costs	125,608
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company		(32,778)	(213,851)
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances	(3,920)	(4,365)	(5,030)
Ending Balance	6,058,147	6,289,961	6,450,168
Partnership Interest [Member] | Total Stockholders' Equity [Member]
Beginning Balance	6,249,448	6,408,636	6,702,959
Adjustment due to change in accounting policy (note 1)			30,901
Adjusted balance			6,733,860
Net income	45,092	240,064	249,652
Other comprehensive income
Other comprehensive income before reclassifications	(17,668)	(14,419)	36
Amounts reclassified from accumulated other comprehensive income	11,011	3,330	5,325
Deferred compensation plan, net			(13)
Contributions from partners	0	0	0
Exchangeable operating partnership units issued for acquisition of real estate	1,275	25,870
Distributions to partners	(404,455)	(393,078)	(378,088)
Reallocation of limited partners' interest		(66)
Restricted stock issued, net of amortization	14,248	16,254	16,745
Common units issued as a result of common stock issued by Parent Company, net of issuance costs	125,608
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company		(32,778)	(213,851)
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances	(3,920)	(4,365)	(5,030)
Ending Balance	6,020,639	6,249,448	6,408,636
Partnership Interest [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance	(11,997)	(927)	(6,289)
Adjustment due to change in accounting policy (note 1)			12
Adjusted balance			(6,277)
Net income	0	0	0
Other comprehensive income
Other comprehensive income before reclassifications	(17,589)	(14,388)	36
Amounts reclassified from accumulated other comprehensive income	10,961	3,318	5,314
Deferred compensation plan, net			0
Contributions from partners	0	0	0
Exchangeable operating partnership units issued for acquisition of real estate	0	0
Distributions to partners	0	0	0
Reallocation of limited partners' interest		0
Restricted stock issued, net of amortization	0	0	0
Common units issued as a result of common stock issued by Parent Company, net of issuance costs	0
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company		0	0
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances	0	0	0
Ending Balance	(18,625)	(11,997)	(927)
Partnership Interest [Member] | Noncontrolling Interest [Member]
Beginning Balance	40,513	41,532	30,095
Adjustment due to change in accounting policy (note 1)			2
Adjusted balance			30,097
Net income	2,225	3,194	2,673
Other comprehensive income
Other comprehensive income before reclassifications	(1,199)	(851)	271
Amounts reclassified from accumulated other comprehensive income	251	(61)	17
Deferred compensation plan, net			0
Contributions from partners	606	2,151	13,000
Exchangeable operating partnership units issued for acquisition of real estate	0	0
Distributions to partners	(4,888)	(5,518)	(4,526)
Reallocation of limited partners' interest		66
Restricted stock issued, net of amortization	0	0	0
Common units issued as a result of common stock issued by Parent Company, net of issuance costs	0
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company		0	0
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances	0	0	0
Ending Balance	37,508	40,513	41,532
Partnership Interest [Member] | General Partner [Member]
Beginning Balance	6,225,345	6,398,897	6,698,341
Adjustment due to change in accounting policy (note 1)			30,889
Adjusted balance			6,729,230
Net income	44,889	239,430	249,127
Other comprehensive income
Other comprehensive income before reclassifications	0	0	0
Amounts reclassified from accumulated other comprehensive income	0	0	0
Deferred compensation plan, net			(13)
Contributions from partners	0	0	0
Exchangeable operating partnership units issued for acquisition of real estate	0	0
Distributions to partners	(402,633)	(392,027)	(377,311)
Reallocation of limited partners' interest		(66)
Restricted stock issued, net of amortization	14,248	16,254	16,745
Common units issued as a result of common stock issued by Parent Company, net of issuance costs	125,608
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company		(32,778)	(213,851)
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances	(3,920)	(4,365)	(5,030)
Ending Balance	6,003,537	6,225,345	6,398,897
Partnership Interest [Member] | Limited Partner [Member]
Beginning Balance	36,100	10,666	10,907
Adjustment due to change in accounting policy (note 1)			0
Adjusted balance			10,907
Net income	203	634	525
Other comprehensive income
Other comprehensive income before reclassifications	(79)	(31)	0
Amounts reclassified from accumulated other comprehensive income	50	12	11
Deferred compensation plan, net			0
Contributions from partners	0	0	0
Exchangeable operating partnership units issued for acquisition of real estate	1,275	25,870
Distributions to partners	(1,822)	(1,051)	(777)
Reallocation of limited partners' interest		0
Restricted stock issued, net of amortization	0	0	0
Common units issued as a result of common stock issued by Parent Company, net of issuance costs	0
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company		0	0
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances	0	0	0
Ending Balance	$ 35,727	$ 36,100	$ 10,666