CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (USD $)	Total	PREFERRED SHARES	COMMON SHARES, $0.01 PAR VALUE	PAID IN CAPITAL	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME	OPERATING PARTNERSHIP	Partially Owned Properties [Member]
Beginning Balance, Noncontrolling Interest at Dec. 31, 2011	$ 193,842,000						$ 119,536,000	$ 74,306,000
Beginning Balance, Parent at Dec. 31, 2011	5,669,015,000					(196,718,000)
Common Share Issuance:
Issuance of Common Shares	123,601,393		21,000	123,580,000
Exercise of share options			7,000	18,931,000
Employee Share Purchase Plan (ESPP)			1,000	4,209,000
Share-based employee compensation expense:
Restricted shares			1,000	2,709,000
Share options				4,092,000
ESPP discount				743,000
Offering costs				(1,887,000)
Supplemental Executive Retirement Plan (SERP)				(6,292,000)
Change in market value	37,603,000			(37,603,000)
Adjustment for Noncontrolling Interests ownership in Operating Partnership				(3,778,000)			3,778,000
Net income attributable to controlling interests	145,299,000				145,299,000
Common Share distributions					(101,404,000)
Preferred Share distributions					(3,466,000)
Accumulated other comprehensive (loss) income - derivative instruments:
Unrealized holding gains arising during the year	3,218,000					3,218,000
Losses reclassified into earnings from other comprehensive income	(3,563,000)					3,563,000
Accumulated other comprehensive income (loss) - other instruments:
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	(36,000)					(36,000)
Issuance of LTIP Units to Noncontrolling Interests							5,000
Conversion of OP Units held by Noncontrolling Interests into OP Units held by General Partner				1,085,000			(1,085,000)
Equity Compensation associated with Noncontrolling Interests							2,163,000
Net Income (Loss) Attributable to Noncontrolling Interest							6,418,000	450,000
Distributions to Noncontrolling Interests							(4,567,000)	(1,762,000)
Change in carrying value	3,217,000						(3,217,000)
Contributions by Noncontrolling Interests								921,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	6,018,954,000	200,000,000	3,005,000	5,152,975,000	656,001,000
Ending Balance, Noncontrolling Interest at Mar. 31, 2012	196,946,000						123,031,000	73,915,000
Ending Balance, Parent at Mar. 31, 2012	$ 5,822,008,000					$ (189,973,000)