Consolidated Statement of Changes in Partner Capital Statement - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Adjustment due to change inaccounting policy (note 1)				$ 30,903
Net income	$ 57,944	$ 70,534	$ 202,127	172,588
Other comprehensive income (loss)	(2,005)	3,889	(16,053)	21,161
Contributions from partners	103		1,999
Issuance of exchangeable operating partnership units	25,869		25,869
Distributions to partners	(1,358)	(1,297)	(4,222)	(3,457)
Reallocation of limited partner's interest			0
Restricted units issued as a result of amortization of restricted stock issued by Parent Company, net of amortization	4,224	4,173	12,127	12,308
Partners Capital Total [Member]
Adjustment due to change inaccounting policy (note 1)				30,901
Net income	56,965	69,722	199,139	170,222
Other comprehensive income (loss)	(1,718)	3,749	(14,877)	20,343
Reallocation of limited partner's interest			66
Restricted units issued as a result of amortization of restricted stock issued by Parent Company, net of amortization	4,224	4,173	12,127	12,308
Partnership Interest [Member]
Beginning Balance	6,352,848	6,568,788	6,450,168	6,733,054
Adjustment due to change inaccounting policy (note 1)				30,903
Adjusted balance				6,763,957
Net income	57,944	70,534	202,127	172,588
Other comprehensive income (loss)	(2,005)	3,889	(16,053)	21,161
Deferred compensation plan, net		(10)		(14)
Contributions from partners	103		1,999
Issuance of exchangeable operating partnership units	25,869		25,869
Distributions to partners	(99,581)	(95,526)	(298,841)	(287,311)
Reallocation of limited partner's interest			0
Restricted units issued as a result of amortization of restricted stock issued by Parent Company, net of amortization	4,224	4,173	12,128	12,308
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company			(32,778)	(124,989)
Common units issued as a result of common stock issued by Parent Company, net of repurchases	445	395		(5,457)
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances			(4,772)
Ending Balance	6,339,847	6,552,243	6,339,847	6,552,243
Partnership Interest [Member] | Partners Capital Total [Member]
Beginning Balance	6,311,369	6,538,865	6,408,636	6,702,959
Adjustment due to change inaccounting policy (note 1)				30,901
Adjusted balance				6,733,860
Net income	57,122	69,869	199,595	170,580
Other comprehensive income (loss)	(1,726)	3,757	(14,913)	20,386
Deferred compensation plan, net		(10)		(14)
Contributions from partners	0		0
Issuance of exchangeable operating partnership units	25,869		25,869
Distributions to partners	(98,223)	(94,229)	(294,619)	(283,854)
Reallocation of limited partner's interest			(66)
Restricted units issued as a result of amortization of restricted stock issued by Parent Company, net of amortization	4,224	4,173	12,128	12,308
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company			(32,778)	(124,989)
Common units issued as a result of common stock issued by Parent Company, net of repurchases	445	395		(5,457)
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances			(4,772)
Ending Balance	6,299,080	6,522,820	6,299,080	6,522,820
Partnership Interest [Member] | AOCI Attributable to Parent [Member]
Beginning Balance	(14,086)	10,317	(927)	(6,289)
Adjustment due to change inaccounting policy (note 1)				12
Adjusted balance				(6,277)
Net income	0	0	0	0
Other comprehensive income (loss)	(1,718)	3,749	(14,877)	20,343
Deferred compensation plan, net		0		0
Contributions from partners	0		0
Issuance of exchangeable operating partnership units	0		0
Distributions to partners	0	0	0	0
Reallocation of limited partner's interest			0
Restricted units issued as a result of amortization of restricted stock issued by Parent Company, net of amortization	0	0	0	0
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company			0	0
Common units issued as a result of common stock issued by Parent Company, net of repurchases	0	0		0
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances			0
Ending Balance	(15,804)	14,066	(15,804)	14,066
Partnership Interest [Member] | Noncontrolling Interest [Member]
Beginning Balance	41,479	29,923	41,532	30,095
Adjustment due to change inaccounting policy (note 1)				2
Adjusted balance				30,097
Net income	822	665	2,532	2,008
Other comprehensive income (loss)	(279)	132	(1,140)	775
Deferred compensation plan, net		0		0
Contributions from partners	103		1,999
Issuance of exchangeable operating partnership units	0		0
Distributions to partners	(1,358)	(1,297)	(4,222)	(3,457)
Reallocation of limited partner's interest			66
Restricted units issued as a result of amortization of restricted stock issued by Parent Company, net of amortization	0	0	0	0
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company			0	0
Common units issued as a result of common stock issued by Parent Company, net of repurchases	0	0		0
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances			0
Ending Balance	40,767	29,423	40,767	29,423
Partnership Interest [Member] | General Partner [Member]
Beginning Balance	6,314,927	6,517,783	6,398,897	6,698,341
Adjustment due to change inaccounting policy (note 1)				30,889
Adjusted balance				6,729,230
Net income	56,965	69,722	199,139	170,222
Other comprehensive income (loss)	0	0	0	0
Deferred compensation plan, net		(10)		(14)
Contributions from partners	0		0
Issuance of exchangeable operating partnership units	0		0
Distributions to partners	(98,018)	(94,035)	(294,005)	(283,272)
Reallocation of limited partner's interest			(66)
Restricted units issued as a result of amortization of restricted stock issued by Parent Company, net of amortization	4,224	4,173	12,128	12,308
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company			(32,778)	(124,989)
Common units issued as a result of common stock issued by Parent Company, net of repurchases	445	395		(5,457)
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances			(4,772)
Ending Balance	6,278,543	6,498,028	6,278,543	6,498,028
Partnership Interest [Member] | Limited Partner [Member]
Beginning Balance	10,528	10,765	10,666	10,907
Adjustment due to change inaccounting policy (note 1)				0
Adjusted balance				10,907
Net income	157	147	456	358
Other comprehensive income (loss)	(8)	8	(36)	43
Deferred compensation plan, net		0		0
Contributions from partners	0		0
Issuance of exchangeable operating partnership units	25,869		25,869
Distributions to partners	(205)	(194)	(614)	(582)
Reallocation of limited partner's interest			0
Restricted units issued as a result of amortization of restricted stock issued by Parent Company, net of amortization	0	0	0	0
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company			0	0
Common units issued as a result of common stock issued by Parent Company, net of repurchases	0	0		0
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances			0
Ending Balance	$ 36,341	$ 10,726	$ 36,341	$ 10,726