Consolidated Statements of Changes in Equity (USD $) In Thousands, unless otherwise specified	Total	Real Estate Fund [Member]	All Other Except Real Estate Fund [Member]	Preferred Shares	Common Shares	Additional Capital	Earnings Less Than Distributions	Accumulated Other Comprehensive Income (Loss)	Non-controlling Interests	Non-controlling Interests Real Estate Fund [Member]	Non-controlling Interests All Other Except Real Estate Fund [Member]
Beginning balance, Value at Dec. 31, 2008	$ 6,214,652			$ 823,807	$ 6,195	$ 6,025,976	$ (1,047,340)	$ (6,899)	$ 412,913
Beginning balance, Shares at Dec. 31, 2008				33,954	155,286
Net income (loss)	103,330						106,169		(2,839)
Common Stock Dividends Shares					6,441
Dividends paid on common shares, Value	(262,397)				258	285,338	(547,993)
Dividends paid on preferred shares, Value	(57,076)						(57,076)
Proceeds from the issuance of shares, Shares					17,250
Proceeds from the issuance of shares, Value	710,226				690	709,536
Common shares issued:
Upon redemption of Class A units, at redemption value, Shares					1,768
Upon redemption of Class A units, at redemption value, Value	90,955				70	90,885
Under employees' share option plan, Shares					468
Under employees' share option plan, Value	(29,638)				4	1,713	(31,355)
Limited partner's distribution:
Conversion Of Series A preferred shares to common shares, Shares				(2)	2
Conversion of Series A preferred shares to common shares, Value	0			(89)	0	89
Deferred compensation shares and options, Shares					(1)
Deferred compensation shares and options, Value	13,092				1	13,091
Change in unrealized net gain on securities available-for-sale	6,147							6,147
Sale of securities available-for-sale	7,715							7,715
Pro rata share of other comprehensive income of nonconsolidated subsidiaries	22,052							22,052
Voluntary surrender of equity awards on March 31, 2009	32,588					32,588
Change in value of interest rate swap	0
Adjustment to carry redeemable Class A units at redemption value	(167,049)					(167,049)
Allocation of cash paid to the equity component upon repurchase of convertible senior debentures	(30,159)					(30,159)
Other	(5,032)			(32)		(1,001)	4	(566)	(3,437)
Ending balance, Value at Dec. 31, 2009	6,649,406			823,686	7,218	6,961,007	(1,577,591)	28,449	406,637
Ending balance, Shares at Dec. 31, 2009				33,952	181,214
Net income (loss)	652,803						647,883		4,920
Dividends paid on common shares, Value	(474,299)						(474,299)
Dividends paid on preferred shares, Value	(55,669)						(55,669)
Redemption of preferred shares, Shares				1,600
Redemption of preferred shares, Value	(35,600)			(39,982)			4,382
Common shares issued:
Upon redemption of Class A units, at redemption value, Shares					1,548
Upon redemption of Class A units, at redemption value, Value	126,764				62	126,702
Under employees' share option plan, Shares					812
Under employees' share option plan, Value	(261)				33	25,290	(25,584)
In connection with dividend reinvestment plan, Shares					22
In connection with dividend reinvestment plan, Value	1,657				1	1,656
Limited partners' contributions:
Limited partners' contribution		93,583	8,783							93,583	8,783
Limited partner's distribution:
Conversion Of Series A preferred shares to common shares, Shares				(12)	18
Conversion of Series A preferred shares to common shares, Value	0			(616)	1	615
Deferred compensation shares and options, Shares					48
Deferred compensation shares and options, Value	9,347				2	9,345
Change in unrealized net gain on securities available-for-sale	46,447							46,447
Sale of securities available-for-sale	(13,160)							(13,160)
Pro rata share of other comprehensive income of nonconsolidated subsidiaries	11,853							11,853
Change in value of interest rate swap	0
Adjustment to carry redeemable Class A units at redemption value	(191,826)					(191,826)
Other	577					(61)	2	(136)	772
Ending balance, Value at Dec. 31, 2010	6,830,405			783,088	7,317	6,932,728	(1,480,876)	73,453	514,695
Ending balance, Shares at Dec. 31, 2010				32,340	183,662
Net income (loss)	684,088						662,302		21,786
Dividends paid on common shares, Value	(508,745)						(508,745)
Dividends paid on preferred shares, Value	(65,694)						(65,694)
Proceeds from the issuance of shares, Shares				9,850
Proceeds from the issuance of shares, Value	238,842			238,842
Common shares issued:
Upon redemption of Class A units, at redemption value, Shares					798
Upon redemption of Class A units, at redemption value, Value	64,830				32	64,798
Under employees' share option plan, Shares					590
Under employees' share option plan, Value	10,439				23	23,705	(13,289)
In connection with dividend reinvestment plan, Shares					21
In connection with dividend reinvestment plan, Value	1,772				1	1,771	0
Limited partners' contributions:
Limited partners' contribution		203,407	778							203,407	778
Limited partner's distribution:
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders		(49,422)	(15,604)							(49,422)	(15,604)
Conversion Of Series A preferred shares to common shares, Shares				(3)	5
Conversion of Series A preferred shares to common shares, Value	0			(165)	0	165
Deferred compensation shares and options, Shares					4
Deferred compensation shares and options, Value	10,085				0	10,608	(523)
Change in unrealized net gain on securities available-for-sale	46,177							46,177
Sale of securities available-for-sale	(9,540)							(9,540)
Pro rata share of other comprehensive income of nonconsolidated subsidiaries	12,859							12,859
Change in value of interest rate swap	(43,704)							(43,704)
Adjustment to carry redeemable Class A units at redemption value	98,092					98,092
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	(271)							(271)
Other	(347)			(105)		(4,609)	5,121	(5,245)	4,491
Ending balance, Value at Dec. 31, 2011	$ 7,508,447			$ 1,021,660	$ 7,373	$ 7,127,258	$ (1,401,704)	$ 73,729	$ 680,131
Ending balance, Shares at Dec. 31, 2011				42,187	185,080