Consolidated Statements of Changes in Equity (USD $) In Thousands, unless otherwise specified	Total	Real Estate Funds [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 Funds [Member]	Non-controlling Interests All Other Except Real Estate Fund [Member]
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 options plan, Shares					389
Under employees' share options plan, Value	(8,811)				16	7,562	(16,389)
Under dividend reinvestment plan, Shares					5
Under dividend reinvestment plan, Value	411					411
Distributions:
Distributions		(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				(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 loss of nonconsolidated subsidiaries	(21,944)							(21,944)
Change in value of interest rate swap	2,386							2,386
Adjustments to carry redeemable Class A units at redemption value	(96,061)					(96,061)
Redeemable noncontrolling interests' share of above adjustments	433							433
Preferred share redemptions	0
Other	(125)							(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
Beginning balance, Value at Dec. 31, 2012	7,904,144			1,240,278	7,440	7,195,438	(1,573,275)	(18,946)	1,053,209
Beginning balance, Shares at Dec. 31, 2012				51,185	186,735
Net income	274,208						262,922		11,286
Dividends on common shares, Value	(136,342)						(136,342)
Dividends on preferred shares, Value	(21,702)						(21,702)
Issuance of Series L preferred shares, Shares				12,000
Issuance of Series L preferred shares, Value	290,710			290,710
Redemption of preferred shares, Shares				(10,500)
Redemption of preferred shares, Value	(253,269)			(253,269)
Common shares issued:
Upon redemption of Class A units, at redemption value, Shares					162
Upon redemption of Class A units, at redemption value, Value	13,404				5	13,399
Under employees' share options plan, Shares					27
Under employees' share options plan, Value	1,176				1	1,175
Under dividend reinvestment plan, Shares					5
Under dividend reinvestment plan, Value	433					433
Contributions:
Contributions		10,251	14,316							10,251	14,316
Distributions:
Distributions		(43,145)	(120,051)							(43,145)	(120,051)
Deferred compensation shares and options, Shares					6
Deferred compensation shares and options, Value	2,208				1	2,512	(305)
Change in unrealized net gain on securities available-for-sale	148,789							148,789
Pro rata share of other comprehensive loss of nonconsolidated subsidiaries	(3,647)							(3,647)
Change in value of interest rate swap	2,523							2,523
Adjustments to carry redeemable Class A units at redemption value	(44,998)					(44,998)
Redeemable noncontrolling interests' share of above adjustments	(8,299)							(8,299)
Preferred share redemptions	(9,230)						(9,230)
Other	(869)						(1,364)	533	(38)
Ending balance, Value at Mar. 31, 2013	$ 8,020,610			$ 1,277,719	$ 7,447	$ 7,167,959	$ (1,479,296)	$ 120,953	$ 925,828
Ending balance, Shares at Mar. 31, 2013				52,685	186,935