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, 2010	$ 6,830,405			$ 783,088	$ 7,317	$ 6,932,728	$ (1,480,876)	$ 73,453	$ 514,695
Beginning balance, shares at Dec. 31, 2010				32,340	183,662
Net income	414,013						412,663		1,350
Dividends on common shares, value	(126,936)						(126,936)
Dividends on preferred shares, value	(13,559)						(13,559)
Common shares issued:
Upon redemption of Class A units, at redemption value, shares					320
Upon redemption of Class A units, at redemption value, value	27,539				13	27,526
Under employees' share option plan, shares					240
Under employees' share option plan, value	14,639				10	15,027	(398)
Under dividend reinvestment plan, shares					5
Under dividend reinvestment plan, value	434				0	434
Limited partners' contributions:
Limited partners' contribution		92,068	170							92,068	170
Distributions:
Distributions to Limited Partners		(11,027)								(11,027)
Conversion Of Series A Preferred Shares To Common Shares, Shares				(1)	2
Conversion of Series A preferred shares to common shares, value	0			(50)	0	50
Deferred compensation shares and options, shares					11
Deferred compensation shares and options, value	2,370				0	2,370
Change in unrealized net gain on securities available-for-sale	68,039							68,039
Pro rata share of other comprehensive income of nonconsolidated subsidiaries	(3,791)							(3,791)
Change in value of interest rate swap	(7,146)							(7,146)
Adjustment to carry redeemable Class A units at redemption value	(42,227)					(42,227)
Other	(147)			(105)		(173)	113	59	(41)
Ending balance, value at Mar. 31, 2011	7,244,844			782,933	7,340	6,935,735	(1,208,993)	130,614	597,215
Ending balance, shares at Mar. 31, 2011				32,339	184,240
Beginning balance, value at Dec. 31, 2011	7,508,447			1,021,660	7,373	7,127,258	(1,401,704)	73,729	680,131
Beginning balance, shares at Dec. 31, 2011				42,187	185,080
Net income	261,119						251,522		9,597
Dividends on common shares, value	(127,973)						(127,973)
Dividends on preferred shares, value	(17,787)						(17,787)
Common shares issued:
Upon redemption of Class A units, at redemption value, shares					158
Upon redemption of Class A units, at redemption value, value	13,028				6	13,022
Under employees' share option plan, shares					389
Under employees' share option plan, value	(8,811)				16	7,562	(16,389)
Under dividend reinvestment plan, shares					5
Under dividend reinvestment plan, value	411				0	411
Distributions:
Distributions to Limited Partners		(21,856)								(21,856)
Conversion Of Series A Preferred Shares To Common Shares, Shares				(2)	3
Conversion of Series A preferred shares to common shares, value	0			(105)		105
Deferred compensation shares and options, shares					7
Deferred compensation shares and options, value	5,577				1	5,915	(339)
Change in unrealized net gain on securities available-for-sale	12,693							12,693
Pro rata share of other comprehensive income of nonconsolidated subsidiaries	(21,944)							(21,944)
Change in value of interest rate swap	2,386							2,386
Adjustment to carry redeemable Class A units at redemption value	(96,061)					(96,061)
Redeemable noncontrolling interests' share of above adjustments	433							433
Other	(125)			0		0	0	(123)	(2)
Ending balance, value at Mar. 31, 2012	$ 7,509,537			$ 1,021,555	$ 7,396	$ 7,058,212	$ (1,312,670)	$ 67,174	$ 667,870
Ending balance, shares at Mar. 31, 2012				42,185	185,642