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 [Member]	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	562,053						531,125		30,928
Dividends on common shares, Value	(384,353)						(384,353)
Dividends on preferred shares, Value	(56,187)						(56,187)
Issuance of preferred shares, Shares				12,000
Issuance of preferred shares, Value	291,144			291,144
Redemption of preferred shares, shares				(3,000)
Redemption of preferred shares, value	(75,000)			(75,000)
Common shares issued:
Upon redemption of Class A units, at redemption value, Shares					624
Upon redemption of Class A units, at redemption value, Value	51,216				25	51,191
Under employees' share option plan, Shares					414
Under employees' share option plan, Value	(7,458)				16	8,915	(16,389)
Under dividend reinvestment plan, Shares					15
Under dividend reinvestment plan, Value	1,270				1	1,269
Contributions:
Contributions		120,606	140							120,606	140
Distributions:
Distributions		(44,910)	(10)							(44,910)	(10)
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	10,670				0	11,009	(339)
Change in unrealized net (loss) gain on available-for-sale securities	(202,167)							(202,167)
Amounts reclassified related to sale of available-for-sale securities	0
Pro rata share of other comprehensive loss of nonconsolidated subsidiaries	(38,861)							(38,861)
Change in value of interest rate swap	(8,868)							(8,868)
Adjustment to carry Class A redeemable units at redemption value	(63,657)					(63,657)
Redeemable noncontrolling interests' share of above adjustments	15,717							15,717
Preferred unit and share redemptions	11,700						11,700
Other	(2,638)						(2,971)	343	(10)
Ending balance, Value at Sep. 30, 2012	7,688,854			1,237,699	7,415	7,136,090	(1,319,118)	(160,107)	786,875
Ending balance, Shares at Sep. 30, 2012				51,185	186,143
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	574,539						524,490		50,049
Dividends on common shares, Value	(409,332)						(409,332)
Dividends on preferred shares, Value	(62,439)						(62,439)
Issuance of preferred shares, Shares				12,000
Issuance of preferred shares, Value	290,536			290,536
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					234
Upon redemption of Class A units, at redemption value, Value	19,627				9	19,618
Under employees' share option plan, Shares					66
Under employees' share option plan, Value	3,681				3	3,678
Under dividend reinvestment plan, Shares					16
Under dividend reinvestment plan, Value	1,376					1,376
Contributions:
Contributions		24,328	15,687							24,328	15,687
Distributions:
Distributions		(47,268)	(126,799)							(47,268)	(126,799)
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					(6)
Deferred compensation shares and options, Value	6,877				(12)	7,194	(305)
Change in unrealized net (loss) gain on available-for-sale securities	160,886							160,886
Amounts reclassified related to sale of available-for-sale securities	(42,404)							(42,404)
Pro rata share of other comprehensive loss of nonconsolidated subsidiaries	(25,023)							(25,023)
Change in value of interest rate swap	14,265							14,265
Adjustment to carry Class A redeemable units at redemption value	(43,709)					(43,709)
Redeemable noncontrolling interests' share of above adjustments	(5,982)							(5,982)
Preferred unit and share redemptions	(1,130)						(1,130)
Deconsolidation of partially owned entity	(165,427)								(165,427)
Other	(5,330)					(25)	(5,672)	531	(164)
Ending balance, Value at Sep. 30, 2013	$ 7,827,834			$ 1,277,455	$ 7,440	$ 7,183,660	$ (1,527,663)	$ 83,327	$ 803,615
Ending balance, Shares at Sep. 30, 2013				52,683	187,048