Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Assets:
Operating real estate, net of accumulated depreciation of $1,801,679 and $1,745,462, respectively	$ 7,307,210		$ 7,104,562
Investments and advances in real estate joint ventures	1,442,240		1,428,155
Real estate under development	97,260		97,263
Other real estate investments	334,082		317,557
Mortgages and other financing receivables	72,361		70,704
Cash and cash equivalents	166,894		141,875
Marketable securities	76,786	[1]	36,541	[1]
Accounts and notes receivable	164,510		171,540
Other assets	400,492		383,037
Total assets	10,061,835		9,751,234
Liabilities:
Notes payable	3,337,420	[2]	3,192,127	[2]
Mortgages payable	1,113,653	[3]	1,003,190	[3]
Dividends payable	99,156		96,518
Other liabilities	469,494		445,843
Total liabilities	5,019,723		4,737,678
Redeemable noncontrolling interests	86,324		81,076
Preferred stock, $1.00 par value, authorized 5,961,200 shares, 102,000 shares issued and outstanding (in series) Aggregate liquidation preference $975,000	102		102
Common stock, $.01 par value, authorized 750,000,000 shares issued and outstanding 408,622,972 and 407,782,102 shares, respectively	4,086		4,078
Paid-in capital	5,667,845		5,651,170
Cumulative distributions in excess of net income	(856,620)		(824,008)
Accumulated other comprehensive income	(27,678)		(66,182)
Total stockholders' equity	4,787,735		4,765,160
Noncontrolling interests	168,053		167,320
Total equity	4,955,788		4,932,480
Total liabilities and equity	$ 10,061,835		$ 9,751,234

[1] As of March 31, 2013 and December 31, 2012, the Company determined that $73.8 million and $22.4 million, respectively, of the marketable securities estimated fair value were classified within Level 1 of the fair value hierarchy and the remaining $3.3 million and $3.4 million, respectively, were classified within Level 3 of the fair value hierarchy.

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

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