Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Assets:
Operating real estate, net of accumulated depreciation of $1,743,276 and $1,693,090, respectively	$ 7,087,796		$ 6,898,445
Investments and advances in real estate joint ventures	1,436,038		1,404,214
Real estate under development	129,877		179,722
Other real estate investments	340,325		344,131
Mortgages and other financing receivables	96,150		102,972
Cash and cash equivalents	383,729		112,882
Marketable securities	34,439	[1]	33,540	[1]
Accounts and notes receivable	131,487		149,807
Other assets	390,230		388,803
Total assets	10,030,071		9,614,516
Liabilities:
Notes payable	3,161,028	[2]	2,983,886	[2]
Mortgages payable	990,586	[3]	1,085,371	[3]
Construction loans payable	40,002		45,128
Dividends payable	98,883		92,159
Other liabilities	439,424		432,755
Total liabilities	4,729,923		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 406,891,427 and 406,937,830 shares, respectively	4,069		4,069
Paid-in capital	5,880,740		5,492,022
Cumulative distributions in excess of net income	(771,282)		(702,999)
	5,114,497		4,794,046
Accumulated other comprehensive income	(99,889)		(107,660)
Total stockholders' equity	5,014,608		4,686,386
Noncontrolling interests	190,481		193,757
Total equity	5,205,089		4,880,143
Total liabilities and equity	10,030,071		9,614,516
Preferred Stock [Member]
Stockholders' equity:
Preferred Stock, Value	0		0
Series F Preferred Stock [Member]
Stockholders' equity:
Preferred Stock, Value	700		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

[1] As of June 30, 2012, $31.3 million of these assets 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.