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, 2014	$ 7,902,936	$ 1,531	$ 200,000	$ 6,270,257	$ (762,464)	$ (2,722)	$ (9,304)	$ 2,205,638
Equity, shares at Dec. 31, 2014		153,114,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		322,000
Conversion of operating partnership units to Common Stock, value	0	$ 4		10,839				(10,843)
Allocated net income for the year	305,462				255,901			49,561
Dividends/distributions declared	(228,254)				(204,676)
Dividends/distributions declared								(23,578)
Shares issued pursuant to stock purchase plan, shares		2,000
Shares issued pursuant to stock purchase plan, value	313			313
Net activity from stock option and incentive plan, shares		36,000
Net activity from stock option and incentive plan, value	27,562	$ 0		3,407				24,155
Contributions from noncontrolling interests in property partnerships	1,089							1,089
Distributions to noncontrolling interests in property partnerships	(34,022)							(34,022)
Effective portion of interest rate contracts	12,106						10,027	2,079
Amortization of interest rate contracts	1,255						1,125	130
Reallocation of noncontrolling interest	0			8,740				(8,740)
Equity, value at Jun. 30, 2015	7,988,447	$ 1,535	200,000	6,293,556	(711,239)	(2,722)	1,848	2,205,469
Equity, shares at Jun. 30, 2015		153,474,000
Equity, value at Dec. 31, 2015	$ 7,886,927	$ 1,536	200,000	6,305,687	(780,952)	(2,722)	(14,114)	2,177,492
Equity, shares at Dec. 31, 2015	153,579,966	153,580,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		78,000
Conversion of operating partnership units to Common Stock, value		$ 1		2,663				(2,664)
Allocated net income for the year	$ 333,579				283,530			50,049
Dividends/distributions declared	(228,652)				(204,939)
Dividends/distributions declared								(23,713)
Shares issued pursuant to stock purchase plan, shares		3,000
Shares issued pursuant to stock purchase plan, value	332			332
Net activity from stock option and incentive plan, shares		14,000
Net activity from stock option and incentive plan, value	16,649			1,772				14,877
Sale of an interest in property partnerships	0			1,320				(1,320)
Contributions from noncontrolling interests in property partnerships	5,040							5,040
Distributions to noncontrolling interests in property partnerships	(25,914)							(25,914)
Effective portion of interest rate contracts	(90,997)						(66,759)	(24,238)
Amortization of interest rate contracts	1,255						1,125	130
Reallocation of noncontrolling interest				4,417				(4,417)
Equity, value at Jun. 30, 2016	$ 7,898,219	$ 1,537	$ 200,000	$ 6,316,191	$ (702,361)	$ (2,722)	$ (79,748)	$ 2,165,322
Equity, shares at Jun. 30, 2016	153,674,930	153,675,000