Consolidated Statements Of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common 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, 2009	$ 5,069,059	$ 1,389	$ 4,373,679	$ 95,433	$ (2,722)	$ (21,777)	$ 623,057
Equity, shares at Dec. 31, 2009		138,880,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		592,000
Conversion of operating partnership units to Common Stock, value	0	6	17,176				(17,182)
Allocated net income for the year	186,984			159,072			27,912
Dividends/distributions declared	(321,838)			(279,268)			(42,570)
Shares issued pursuant to stock purchase plan, shares		9,000
Shares issued pursuant to stock purchase plan, value	630		630
Net activity from stock option and incentive plan, shares		718,000
Net activity from stock option and incentive plan, value	54,815	7	25,038				29,770
Acquisition Of noncontrolling interest In property partnership	(25,482)		(19,098)				(6,384)
Acquisition of equity component of exchangeable senior notes	(439)		(439)
Distributions to noncontrolling interests in property partnerships	(3,365)						(3,365)
Effective portion of interest rate contracts	421					367	54
Amortization of interest rate contracts	3,408					2,974	434
Reallocation of noncontrolling interest	0		20,176				(20,176)
Equity, value at Dec. 31, 2010	4,964,193	1,402	4,417,162	(24,763)	(2,722)	(18,436)	591,550
Equity, shares at Dec. 31, 2010		140,199,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		2,919,000
Conversion of operating partnership units to Common Stock, value	0	29	85,469				(85,498)
Allocated net income for the year	310,487			272,679			37,808
Dividends/distributions declared	(340,128)			(300,996)			(39,132)
Sale of Common Stock, net of offering costs, shares		4,660,000
Sale of Common Stock, net of offering costs, value	439,037	47	438,990
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	620		620
Net activity from stock option and incentive plan, shares		324,000
Net activity from stock option and incentive plan, value	38,719	3	17,289				21,427
Distributions to noncontrolling interests in property partnerships	(2,007)						(2,007)
Effective portion of interest rate contracts	0
Amortization of interest rate contracts	2,595					2,298	297
Reallocation of noncontrolling interest	0		(23,073)				23,073
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	148,107,611	148,108,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		1,111,000
Conversion of operating partnership units to Common Stock, value	0	11	34,610				(34,621)
Conversion of redeemable preferred units to common units	5,852						5,852
Allocated net income for the year	326,839			289,650			37,189
Dividends/distributions declared	(387,989)			(346,555)			(41,434)
Sale of Common Stock, net of offering costs, shares		2,348,000
Sale of Common Stock, net of offering costs, value	247,027	24	247,003
Shares issued pursuant to stock purchase plan, shares		7,000
Shares issued pursuant to stock purchase plan, value	781		781
Net activity from stock option and incentive plan, shares		27,000
Net activity from stock option and incentive plan, value	29,124		5,419				23,705
Distributions to noncontrolling interests in property partnerships	(2,890)						(2,890)
Effective portion of interest rate contracts	0
Amortization of interest rate contracts	2,594					2,321	273
Reallocation of noncontrolling interest	0		(2,197)				2,197
Equity, value at Dec. 31, 2012	$ 5,634,854	$ 1,516	$ 5,222,073	$ (109,985)	$ (2,722)	$ (13,817)	$ 537,789
Equity, shares at Dec. 31, 2012	151,601,209	151,601,000