CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (Unaudited) (USD $) In Thousands	Total	PREFERRED SHARES	COMMON SHARES, $0.01 PAR VALUE	PAID IN CAPITAL	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE (LOSS)	PARTIALLY OWNED PROPERTIES	OPERATING PARTNERSHIP	OPERATING PARTNERSHIP ACCUMULATED OTHER COMPREHENSIVE (LOSS)	OPERATING PARTNERSHIP PARTIALLY OWNED PROPERTIES	OPERATING PARTNERSHIP GENERAL PARTNER	OPERATING PARTNERSHIP LIMITED PARTNERS
Beginning Balance at Dec. 31, 2010	$ 5,208,576	$ 200,000	$ 2,902	$ 4,741,521	$ 203,581	$ (57,818)	$ 7,991	$ 110,399
Common Share Issuance:
Conversion of OP Units into Common Shares			3	7,224				(7,227)
Issuance of Common Shares			30	154,478
Exercise of share options			26	83,508							83,534
Employee Share Purchase Plan (ESPP)			1	3,500							3,501
Conversion of restricted shares to LTIP Units			(1)	(3,933)				3,934			(3,934)	3,934
Share-based employee compensation expense:
Restricted shares			2	5,343
Share options				5,386
ESPP discount				872
Offering costs				(2,611)							(2,611)
Supplemental Executive Retirement Plan (SERP)				2,984
Acquisition of Noncontrolling Interests - Partially Owned Properties				(5,575)			(3,000)			(3,000)	(5,575)
Change in market value of Redeemable Noncontrolling Interests - Operating Partnership	41,377			(41,377)
Net income attributable to controlling interests	683,255				683,255			714,788
Common Share distributions					(199,284)
Preferred Share distributions					(6,933)
Accumulated other comprehensive (loss) - derivative instruments:
Unrealized holding (losses) arising during the period	(25,119)					(25,119)		(25,119)	(25,199)
Losses reclassified into earnings from other comprehensive income	1,891					1,891		1,891	1,891
Accumulated other comprehensive income - other instruments:
Unrealized holding gains (losses) arising during the period	493					493		493
Equity compensation associated with Noncontrolling Interests								1,988				1,988
Net income attributable to Noncontrolling Interests	714,819						31	714,819
Distributions to Noncontrolling Interests							(487)	(9,238)		(487)
Change in carrying value of Redeemable Noncontrolling Interests - Operating Partnership	(13,224)							(13,224)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				(3,853)				3,853
Other							(1,240)
Ending Balance at Jun. 30, 2011	5,875,809	200,000	2,963	4,947,467	680,619	(80,553)	3,295	122,018
Beginning Balance at Mar. 31, 2011
Share-based employee compensation expense:
Net income attributable to controlling interests	555,924							581,682
Accumulated other comprehensive (loss) - derivative instruments:
Unrealized holding (losses) arising during the period	(31,201)							(31,201)
Losses reclassified into earnings from other comprehensive income	935							935
Accumulated other comprehensive income - other instruments:
Unrealized holding gains (losses) arising during the period	347							347
Net income attributable to Noncontrolling Interests	581,753							581,753
Ending Balance at Jun. 30, 2011	$ 5,875,809	$ 200,000						$ 122,018