Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Net income	$ 180,968	$ 188,620
Depreciation and amortization	191,420	197,964
Impairment charges	109,000
Gain on sale of operating properties	(29,859)	(44,596)
Equity in income of joint ventures, net	(179,791)	(89,587)
Gains on change in control of interests	(21,711)	(14,156)
Equity in income from other real estate investments, net	(29,910)	(35,340)
Distributions from joint ventures and other real estate investments	211,362	150,721
Change in accounts and notes receivable	11,414	11,249
Change in accounts payable and accrued expenses	69,053	34,915
Change in other operating assets and liabilities	(36,258)	(29,940)
Net cash flow provided by operating activities	533,841	407,590
Acquisition of operating real estate	(182,423)	(338,959)
Investment in marketable securities	(33,588)
Proceeds from sale/repayments of marketable securities	10,800	156
Investments and advances to real estate joint ventures	(289,494)	(159,121)
Reimbursements of investments and advances to real estate joint ventures	409,748	135,987
Investment in other real estate investments	(23,488)	(4,215)
Reimbursements of investments and advances to other real estate investments	19,557	26,637
Investment in mortgage loans receivable	(11,469)	(15,623)
Collection of mortgage loans receivable	13,900	24,613
Investment in other investments	(21,366)	(924)
Reimbursements of other investments	9,175	9,538
Proceeds from sale of operating properties	247,965	277,174
Net cash flow provided by (used for) investing activities	70,286	(130,050)
Principal payments on debt, excluding normal amortization of rental property debt	(132,492)	(212,105)
Principal payments on rental property debt	(18,264)	(17,585)
Principal payments on construction loan financings		(213)
Proceeds from mortgage/construction loan financings	35,974	6,276
Repayments under unsecured revolving credit facility, net	(99,076)	(226,558)
Borrowings under unsecured term loan/notes	621,562	400,000
Repayments under unsecured term loan/notes	(446,717)	(17,000)
Financing origination costs	(7,365)	(1,904)
Redemption of/distributions to noncontrolling interests	(27,184)	(25,868)
Dividends paid	(299,754)	(285,092)
Proceeds from issuance of stock	29,044	625,102
Redemption of preferred stock		(175,000)
Repurchase of common stock		(30,946)
Net cash flow (used for) provided by financing activities	(344,272)	39,107
Change in cash and cash equivalents	259,855	316,647
Cash and cash equivalents, beginning of period	141,875	112,882
Cash and cash equivalents, end of period	401,730	429,529
Interest paid during the period (net of capitalized interest of $888 and $1,273, respectively)	142,805	149,976
Income taxes paid during the period	1,240	1,970
Operating Real Estate [Member]
Improvements to real estate	(78,490)	(82,890)
Real Estate Under Development [Member]
Improvements to real estate	(541)	(2,423)
Impairment Charges [Member]
Impairment charges	$ 167,153	$ 37,740