Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Assets:
Operating real estate, net of accumulated depreciation of $1,745,992 and $1,693,090, respectively	$ 7,078,206		$ 6,898,445
Investments and advances in real estate joint ventures	1,433,450		1,404,214
Real estate under development	132,113		179,722
Other real estate investments	326,268		344,131
Mortgages and other financing receivables	98,188		102,972
Cash and cash equivalents	429,529		112,882
Marketable securities	35,811	[1]	33,540	[1]
Accounts and notes receivable	138,558		149,807
Other assets	443,853		388,803
Total assets	10,115,976		9,614,516
Liabilities:
Notes payable	3,159,943	[2]	2,983,886	[2]
Mortgages payable	1,015,313	[3]	1,085,371	[3]
Construction loans payable	42,935		45,128
Dividends payable	94,856		92,159
Other liabilities	464,691		432,755
Total liabilities	4,777,738		4,639,299
Redeemable noncontrolling interests	95,059		95,074
Stockholders' equity:
Common Stock, $.01 par value, authorized 750,000,000 shares issued and outstanding 407,608,794 and 406,937,830 shares, respectively	4,076		4,069
Paid-in capital	5,938,244		5,492,022
Cumulative distributions in excess of net income	(813,097)		(702,999)
	5,129,502		4,794,046
Accumulated other comprehensive income	(56,785)		(107,660)
Total stockholders' equity	5,072,717		4,686,386
Noncontrolling interests	170,462		193,757
Total equity	5,243,179		4,880,143
Total liabilities and equity	10,115,976		9,614,516
Preferred Stock [Member]
Stockholders' equity:
Preferred Stock, Value	0		0
Series F Preferred Stock [Member]
Stockholders' equity:
Preferred Stock, Value			700
Series G Preferred Stock [Member]
Stockholders' equity:
Preferred Stock, Value	184		184
Series H Preferred Stock [Member]
Stockholders' equity:
Preferred Stock, Value	70		70
Series I Preferred Stock [Member]
Stockholders' equity:
Preferred Stock, Value	16
Series J Preferred Stock [Member]
Stockholders' equity:
Preferred Stock, Value	$ 9

[1] As of September 30, 2012, $32.7 million of these assets' estimated fair value were classified within Level 1 of the fair value hierarchy and the remaining $3.4 million were classified within Level 3 of the fair value hierarchy.

[2] The Company determined that its valuation of these Notes payable was classified within Level 2 of the fair value hierarchy.

[3] The Company determined that its valuation of these liabilities was classified within Level 3 of the fair value hierarchy.