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 [Member]
Equity, value at Dec. 31, 2016	$ 7,931,924	$ 1,538	$ 200,000	$ 6,333,424	$ (693,694)	$ (2,722)	$ (52,251)	$ 2,145,629
Equity, shares at Dec. 31, 2016		153,790,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		23,000
Conversion of operating partnership units to Common Stock, value	0	$ 0		793				(793)
Allocated net income for the year	115,564				99,708			15,856
Dividends/distributions declared	(131,665)				(118,012)			(13,653)
Shares issued pursuant to stock purchase plan, shares		3,000
Shares issued pursuant to stock purchase plan, value	373			373
Net activity from stock option and incentive plan, shares		33,000
Net activity from stock option and incentive plan, value	12,281	$ 0		996				11,285
Cumulative effect of a change in accounting principle	(2,035)				(272)			(1,763)
Contributions from noncontrolling interests in property partnerships	8,145							8,145
Distributions to noncontrolling interests in property partnerships	(13,635)							(13,635)
Effective portion of interest rate contracts	180						97	83
Amortization of interest rate contracts	1,306						1,171	135
Reallocation of noncontrolling interest	0			4,384				(4,384)
Equity, value at Mar. 31, 2017	7,922,438	$ 1,538	200,000	6,339,970	(712,270)	(2,722)	(50,983)	2,146,905
Equity, shares at Mar. 31, 2017		153,849,000
Equity, value at Dec. 31, 2017	$ 8,102,456	$ 1,543	200,000	6,377,908	(712,343)	(2,722)	(50,429)	2,288,499
Equity, shares at Dec. 31, 2017	154,325,286	154,325,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		24,000
Conversion of operating partnership units to Common Stock, value		$ 1		831				(832)
Allocated net income for the year	$ 216,312				178,646			37,666
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
Cumulative effect of a change in accounting principle	5,496				4,933			563
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	299
Reallocation of noncontrolling interest				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)	$ 2,305,062
Equity, shares at Mar. 31, 2018	154,362,303	154,362,000