Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flow from operating activities:
Net income	$ 123,780	$ 131,535
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	127,042	131,191
Impairment charges	81,546	34,570
Gain on sale of operating properties	(5,446)	(31,318)
Equity in income of joint ventures, net	(83,616)	(65,090)
Gains on change in control of interests	(21,711)	(14,156)
Equity in income from other real estate investments, net	(19,363)	(25,103)
Distributions from joint ventures and other real estate investments	82,245	115,627
Change in accounts and notes receivable	11,142	18,320
Change in accounts payable and accrued expenses	6,755	114
Change in other operating assets and liabilities	(36,846)	(20,258)
Net cash flow provided by operating activities	265,528	275,432
Cash flow from investing activities:
Acquisition of operating real estate	(145,303)	(267,427)
Investment in marketable securities	(33,588)
Proceeds from sale/repayments of marketable securities	10,758	118
Investments and advances to real estate joint ventures	(239,903)	(121,242)
Reimbursements of investments and advances to real estate joint ventures	295,186	80,023
Investment in other real estate investments	(23,227)	(4,123)
Reimbursements of investments and advances to other real estate investments	1,200	6,906
Investment in mortgage loans receivable	(11,017)	(25)
Collection of mortgage loans receivable	8,779	9,733
Investment in other investments	(21,366)	(762)
Reimbursements of other investments	463	9,151
Proceeds from sale of operating properties	110,389	206,107
Net cash flow used for investing activities	(97,452)	(144,883)
Cash flow from financing activities:
Principal payments on debt, excluding normal amortization of rental property debt	(66,206)	(200,312)
Principal payments on rental property debt	(12,094)	(11,651)
Proceeds from mortgage/construction loan financings	17,374	6,276
Repayments under unsecured revolving credit facility, net	(62,966)	(226,220)
Borrowings under unsecured term loan/notes	428,118	400,000
Repayments under unsecured term loan/notes	(253,225)
Financing origination costs	(6,096)	(1,391)
Redemption of/distributions to noncontrolling interests	(27,184)	(7,548)
Dividends paid	(199,164)	(184,307)
Proceeds from issuance of stock	27,942	394,409
Repurchase of common stock		(28,958)
Net cash flow (used for) provided by financing activities	(153,501)	140,298
Change in cash and cash equivalents	14,575	270,847
Cash and cash equivalents, beginning of period	141,875	112,882
Cash and cash equivalents, end of period	156,450	383,729
Interest paid during the period (net of capitalized interest of $579 and $926, respectively)	108,906	113,411
Income taxes paid during the period	798	1,584
Operating Real Estate [Member]
Cash flow from investing activities:
Improvements to real estate	(49,497)	(61,593)
Real Estate Under Development [Member]
Cash flow from investing activities:
Improvements to real estate	$ (326)	$ (1,749)