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	314,137						289,819		24,318
Dividends on common shares, Value	(256,119)						(256,119)
Dividends on preferred shares, Value	(35,574)						(35,574)
Common shares issued:
Upon redemption of Class A units, at redemption value, Shares					303
Upon redemption of Class A units, at redemption value, Value	24,976				12	24,964
Under employees' share option plan, Shares					412
Under employees' share option plan, Value	(7,573)				16	8,800	(16,389)
Under dividend reinvestment plan, Shares					10
Under dividend reinvestment plan, Value	843				1	842
Contributions:
Contributions		108,319	30							108,319	30
Distributions:
Distributions		(44,910)								(44,910)
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	8,145				0	8,484	(339)
Change in unrealized net gain (loss) on available-for-sale securities	(220,525)							(220,525)
Pro rata share of other comprehensive loss of nonconsolidated subsidiaries	(26,254)							(26,254)
Change in value of interest rate swap	(6,002)							(6,002)
Adjustments to carry redeemable Class A units at redemption value	(110,581)					(110,581)
Redeemable noncontrolling interests' share of above adjustments	15,894							15,894
Preferred unit and share redemptions	0
Other	372						2	373	(3)
Ending balance, Value at Jun. 30, 2012	7,273,625			1,021,555	7,402	7,059,872	(1,420,304)	(162,785)	767,885
Ending balance, Shares at Jun. 30, 2012				42,185	185,815
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	447,332						421,116		26,216
Dividends on common shares, Value	(272,825)						(272,825)
Dividends on preferred shares, Value	(42,070)						(42,070)
Issuance of Series L preferred shares, Shares				12,000
Issuance of Series L preferred shares, Value	290,536			290,536
Redemption of Series F and Series H preferred shares, Shares				(10,500)
Redemption of Series F and Series H preferred shares, value	(253,269)			(253,269)
Common shares issued:
Upon redemption of Class A units, at redemption value, Shares					180
Upon redemption of Class A units, at redemption value, Value	14,980				7	14,973
Under employees' share option plan, Shares					62
Under employees' share option plan, Value	3,567				3	3,564
Under dividend reinvestment plan, Shares					11
Under dividend reinvestment plan, Value	903					903
Contributions:
Contributions		18,781	15,186							18,781	15,186
Distributions:
Distributions		(43,145)	(120,051)							(43,145)	(120,051)
Conversion of Series A preferred shares to common shares, Shares				(2)	3
Conversion of Series A preferred shares to common shares, Value				(90)	0	90
Deferred compensation shares and options, Shares					0
Deferred compensation shares and options, Value	4,481				0	4,786	(305)
Change in unrealized net gain (loss) on available-for-sale securities	169,138							169,138
Pro rata share of other comprehensive loss of nonconsolidated subsidiaries	(23,354)							(23,354)
Change in value of interest rate swap	14,560							14,560
Adjustments to carry redeemable Class A units at redemption value	(29,393)					(29,393)
Redeemable noncontrolling interests' share of above adjustments	(9,034)							(9,034)
Preferred unit and share redemptions	(1,130)						(1,130)
Deconsolidation of partially owned entity	(165,427)								(165,427)
Other	(2,683)					(25)	(3,154)	530	(34)
Ending balance, Value at Jun. 30, 2013	$ 7,921,227			$ 1,277,455	$ 7,450	$ 7,190,336	$ (1,471,643)	$ 132,894	$ 784,735
Ending balance, Shares at Jun. 30, 2013				52,683	186,991