Consolidated Statements Of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	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]
Equity, value at Dec. 31, 2011	$ 5,413,516	$ 1,481		$ 4,936,457	$ (53,080)	$ (2,722)	$ (16,138)	$ 547,518
Equity, shares at Dec. 31, 2011		148,108,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		366,000
Conversion of operating partnership units to Common Stock, value	0	4		11,232				(11,236)
Conversion of redeemable preferred units to common units	5,852
Allocated net income for the year	253,091				224,244			28,847
Dividends/distributions declared					(248,014)
Sale of common stock, net of offering costs		2,348,000
Sale of common stock, net of offering costs	247,186	24		247,162
Shares issued in connection with exchange of Exchangeable Senior Notes, value	0
Shares issued pursuant to stock purchase plan, shares		8,000
Shares issued pursuant to stock purchase plan, value	781			781
Net activity from stock option and incentive plan, shares		26,000
Net activity from stock option and incentive plan, value	24,294			4,473				19,821
Noncontrolling interests in property partnerships recorded upon consolidation	0
Distributions to noncontrolling interests in property partnerships	(2,250)							(2,250)
Amortization of interest rate contracts	1,967						1,759	208
Reallocation of noncontrolling interest				(5,565)				5,565
Equity, value at Sep. 30, 2012	5,666,323	1,509		5,194,540	(76,850)	(2,722)	(14,379)	564,225
Equity, shares at Sep. 30, 2012		150,856,000
Equity, value at Dec. 31, 2012	5,634,854	1,516	0	5,222,073	(109,985)	(2,722)	(13,817)	537,789
Equity, shares at Dec. 31, 2012	151,601,209	151,601,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		337,000
Conversion of operating partnership units to Common Stock, value	0	4		10,402				(10,406)
Allocated net income for the year	726,717				658,272			68,445
Dividends/distributions declared	(336,037)				(302,081)			(33,956)
Issuance of 5.25% Series B cumulative redeemable preferred stock	193,623		200,000
Shares issued in connection with exchange of Exchangeable Senior Notes, shares		419,000
Shares issued in connection with exchange of Exchangeable Senior Notes, value	43,834	4		43,830
Equity component of exchange of Exchangeable Senior Notes				(43,869)
Issuance of 5.25% Series B cumulative redeemable preferred stock				(6,377)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	681			681
Net activity from stock option and incentive plan, shares		28,000
Net activity from stock option and incentive plan, value	30,632			6,510				24,122
Noncontrolling interests in property partnerships recorded upon consolidation	480,861							480,861
Contributions from noncontrolling interests in property partnerships	10,932							10,932
Distributions to noncontrolling interests in property partnerships	(2,250)							(2,250)
Amortization of interest rate contracts	1,884						1,695	189
Reallocation of noncontrolling interest	0			16,924				(16,924)
Equity, value at Sep. 30, 2013	$ 6,741,862	$ 1,524	$ 200,000	$ 5,250,174	$ 246,206	$ (2,722)	$ (12,122)	$ 1,058,802
Equity, shares at Sep. 30, 2013	152,390,595	152,391,000