Consolidated Statements Of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-In Capital [Member]	Dividends In Excess Of Earnings [Member]	Treasury Stock, at cost [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interests [Member]	Noncontrolling interest - property partnerships [Member]
Equity, shares at Dec. 31, 2018		154,458,000
Equity, value at Dec. 31, 2018	$ 8,213,968	$ 1,545	$ 200,000	$ 6,407,623	$ (675,534)	$ (2,722)	$ (47,741)	$ 619,352	$ 1,711,445
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	(4,379)				(3,864)			(445)	(70)
Redemption of operating partnership units to common stock, shares		42,000
Redemption of operating partnership units to common stock, value	0	$ 1		1,434				(1,435)
Allocated net income for the year	475,990				378,075			43,133	54,782
Dividends/distributions declared	(499,934)				(448,343)			(51,591)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	688			688
Net activity from stock option and incentive plan, shares		66,000
Net activity from stock option and incentive plan, value	26,887			(2,665)				29,552
Sale of an interest in property partnerships	0			(4,216)					4,216
Acquisition of noncontrolling interest in property partnership	(186,963)			(162,462)					(24,501)
Contributions from noncontrolling interests in property partnerships	26,968								26,968
Distributions to noncontrolling interests in property partnerships	(53,149)								(53,149)
Effective portion of interest rate contracts	(9,307)						(8,354)	(953)	0
Amortization of interest rate contracts	4,998						4,099	467	432
Reallocation of noncontrolling interest	0			34,390				(34,390)
Equity, shares at Sep. 30, 2019		154,572,000
Equity, value at Sep. 30, 2019	7,995,767	$ 1,546	200,000	6,274,792	(749,666)	(2,722)	(51,996)	603,690	1,720,123
Equity, shares at Jun. 30, 2019		154,563,000
Equity, value at Jun. 30, 2019	8,020,667	$ 1,546	200,000	6,278,961	(710,592)	(2,722)	(51,340)	608,593	1,696,221
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of operating partnership units to common stock, shares		7,000
Redemption of operating partnership units to common stock, value	0	$ 0		223				(223)
Allocated net income for the year	141,370				110,394			12,506	18,470
Dividends/distributions declared	(166,668)				(149,468)			(17,200)
Shares issued pursuant to stock purchase plan, shares		2,000
Shares issued pursuant to stock purchase plan, value	315			315
Net activity from stock option and incentive plan, shares		0
Net activity from stock option and incentive plan, value	(445)			(7,219)				6,774
Sale of an interest in property partnerships	0			(4,216)					4,216
Acquisition of noncontrolling interest in property partnership	43			43					0
Contributions from noncontrolling interests in property partnerships	14,820								14,820
Distributions to noncontrolling interests in property partnerships	(13,748)								(13,748)
Effective portion of interest rate contracts	(2,253)						(2,022)	(231)
Amortization of interest rate contracts	1,666						1,366	156	144
Reallocation of noncontrolling interest	0			6,685				(6,685)
Equity, shares at Sep. 30, 2019		154,572,000
Equity, value at Sep. 30, 2019	$ 7,995,767	$ 1,546	200,000	6,274,792	(749,666)	(2,722)	(51,996)	603,690	1,720,123
Equity, shares at Dec. 31, 2019	154,790,298	154,790,000
Equity, value at Dec. 31, 2019	$ 8,014,236	$ 1,548	200,000	6,294,719	(760,523)	(2,722)	(48,335)	600,860	1,728,689
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	(1,679)				(1,505)			(174)	0
Redemption of operating partnership units to common stock, shares		774,000
Redemption of operating partnership units to common stock, value	0	$ 8		26,674				(26,682)
Allocated net income for the year	993,786				862,416			97,090	34,280
Dividends/distributions declared	(516,929)				(465,108)			(51,821)
Shares issued pursuant to stock purchase plan, shares		7,000
Shares issued pursuant to stock purchase plan, value	759			759
Net activity from stock option and incentive plan, shares		65,000
Net activity from stock option and incentive plan, value	41,924	$ 0		9,646				32,278
Contributions from noncontrolling interests in property partnerships	7,364								7,364
Distributions to noncontrolling interests in property partnerships	(40,091)								(40,091)
Effective portion of interest rate contracts	(9,352)						(8,416)	(936)	0
Amortization of interest rate contracts	5,020						4,129	459	432
Reallocation of noncontrolling interest	$ 0			16,278				(16,278)
Equity, shares at Sep. 30, 2020	155,636,300	155,636,000
Equity, value at Sep. 30, 2020	$ 8,495,038	$ 1,556	200,000	6,348,076	(364,720)	(2,722)	(52,622)	634,796	1,730,674
Equity, shares at Jun. 30, 2020		155,622,000
Equity, value at Jun. 30, 2020	8,547,146	$ 1,556	200,000	6,340,665	(302,511)	(2,722)	(54,921)	640,491	1,724,588
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of operating partnership units to common stock, shares		9,000
Redemption of operating partnership units to common stock, value	0	$ 0		338				(338)
Allocated net income for the year	118,060				92,934			9,565	15,561
Dividends/distributions declared	(172,326)				(155,143)			(17,183)
Shares issued pursuant to stock purchase plan, shares		5,000
Shares issued pursuant to stock purchase plan, value	434			434
Net activity from stock option and incentive plan, shares		0
Net activity from stock option and incentive plan, value	8,639			1,390				7,249
Contributions from noncontrolling interests in property partnerships	1,407								1,407
Distributions to noncontrolling interests in property partnerships	(11,026)								(11,026)
Effective portion of interest rate contracts	1,027						917	110
Amortization of interest rate contracts	1,677						1,382	151	144
Reallocation of noncontrolling interest	$ 0			5,249				(5,249)
Equity, shares at Sep. 30, 2020	155,636,300	155,636,000
Equity, value at Sep. 30, 2020	$ 8,495,038	$ 1,556	$ 200,000	$ 6,348,076	$ (364,720)	$ (2,722)	$ (52,622)	$ 634,796	$ 1,730,674