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 (Income) Loss [Member]	Noncontrolling Interests - Common units [Member]	Noncontrolling interest - property partnerships [Member]
Equity, value at Dec. 31, 2017	$ 8,102,456	$ 1,543	$ 200,000	$ 6,377,908	$ (712,343)	$ (2,722)	$ (50,429)	$ 604,739	$ 1,683,760
Equity, shares at Dec. 31, 2017		154,325,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	5,496				4,933			563
Conversion of operating partnership units to Common Stock, shares		24,000
Conversion of operating partnership units to Common Stock, value	0	$ 1		831				(832)
Allocated net income for the year	216,312				178,646			20,432	17,234
Dividends/distributions declared	(140,466)				(126,115)			(14,351)
Shares issued pursuant to stock purchase plan, shares		3,000
Shares issued pursuant to stock purchase plan, value	429			429
Net activity from stock option and incentive plan, shares		10,000
Net activity from stock option and incentive plan, value	13,620			(185)				13,805
Contributions from noncontrolling interests in property partnerships	15,267								15,267
Distributions to noncontrolling interests in property partnerships	(30,690)								(30,690)
Amortization of interest rate contracts	1,666						1,367	155	144
Reallocation of noncontrolling interest	0			5,164				(5,164)
Equity, value at Mar. 31, 2018	8,184,090	$ 1,544	200,000	6,384,147	(654,879)	(2,722)	(49,062)	619,347	1,685,715
Equity, shares at Mar. 31, 2018		154,362,000
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
Equity, shares at Dec. 31, 2018	154,458,478	154,458,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	$ (4,379)				(3,864)			(445)	(70)
Conversion of operating partnership units to Common Stock, shares		14,000
Conversion of operating partnership units to Common Stock, value	0			492				(492)
Allocated net income for the year	131,159				100,730			11,599	18,830
Dividends/distributions declared	(166,600)				(149,415)			(17,185)
Shares issued pursuant to stock purchase plan, shares		4,000
Shares issued pursuant to stock purchase plan, value	373			373
Net activity from stock option and incentive plan, shares		39,000
Net activity from stock option and incentive plan, value	16,469			3,059				13,410
Contributions from noncontrolling interests in property partnerships	4,387								4,387
Distributions to noncontrolling interests in property partnerships	(24,128)								(24,128)
Effective portion of interest rate contracts	(2,628)						(2,359)	(269)
Amortization of interest rate contracts	1,666						1,366	156	144
Reallocation of noncontrolling interest	0			3,065				(3,065)
Equity, value at Mar. 31, 2019	$ 8,170,287	$ 1,545	$ 200,000	$ 6,414,612	$ (728,083)	$ (2,722)	$ (48,734)	$ 623,061	$ 1,710,608
Equity, shares at Mar. 31, 2019	154,515,486	154,515,000