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		259,000
Conversion of operating partnership units to Common Stock, value	0	$ 3		8,686				(8,689)
Allocated net income for the year	206,939				173,771			33,168
Dividends/distributions declared	(114,005)				(102,300)
Dividends/distributions declared								(11,705)
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		27,000
Net activity from stock option and incentive plan, value	21,616	$ 0		1,842				19,774
Contributions from noncontrolling interests in property partnerships	629							629
Distributions to noncontrolling interests in property partnerships	(16,574)							(16,574)
Effective portion of interest rate contracts	(3,533)						(3,165)	(368)
Amortization of interest rate contracts	627						562	65
Reallocation of noncontrolling interest	0			5,162				(5,162)
Equity, value at Mar. 31, 2015	7,998,948	$ 1,534	200,000	6,286,260	(690,993)	(2,722)	(11,907)	2,216,776
Equity, shares at Mar. 31, 2015		153,402,000
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		13,000
Conversion of operating partnership units to Common Stock, value		$ 0		446				(446)
Allocated net income for the year	$ 216,222				184,365			31,857
Dividends/distributions declared	(114,326)				(102,461)
Dividends/distributions declared								(11,865)
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		9,000
Net activity from stock option and incentive plan, value	9,080			696				8,384
Contributions from noncontrolling interests in property partnerships	2,489							2,489
Distributions to noncontrolling interests in property partnerships	(12,915)							(12,915)
Effective portion of interest rate contracts	(58,646)						(43,154)	(15,492)
Amortization of interest rate contracts	627						562	65
Reallocation of noncontrolling interest				(438)				438
Equity, value at Mar. 31, 2016	$ 7,929,790	$ 1,536	$ 200,000	$ 6,306,723	$ (699,048)	$ (2,722)	$ (56,706)	$ 2,180,007
Equity, shares at Mar. 31, 2016	153,604,966	153,605,000