Noncontrolling Interests - Outstanding Cumulative Redeemable Preferred Units (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Preferred Units [Line Items]
Preferred Units, Outstanding	1,290,000	1,290,000	9,740,000
Preferred Stock Redemption Premium	$ 40,000
Preferred Unit Redemptions [Abstract]
Preferred Stock Redemption Discount		(3,689,000)
Series E Preferred Stock [Member]
Preferred Units [Line Items]
Noncontrolling Interest in Operating Partnerships	20,000,000	20,000,000
Preferred Units, Outstanding	400,000	400,000
Preferred Stock, Liquidation Preference	50	50
Preferred Stock, Dividend Rate		7.00%
Preferred Stock Redeemable As Of		Jun. 16, 2010
Preferred Stock, Exchangeable After		6/16/15 into Series E Cumulative Redeemable Preferred Shares of the Trust
Series F Preferred Stock [Member]
Preferred Units [Line Items]
Noncontrolling Interest in Operating Partnerships	17,500,000	17,500,000
Preferred Units, Outstanding	350,000	350,000
Preferred Stock, Liquidation Preference	50	50
Preferred Stock, Dividend Rate		6.65%
Preferred Stock Redeemable As Of		Jun. 30, 2010
Preferred Stock, Exchangeable After		12/12/15 into Series F Cumulative Redeemable Preferred Shares of the Trust
Preferred Unit Redemptions [Abstract]
Preferred Stock, Redemption Amount		32,500,000
Payments for Repurchase of Preferred Stock		26,000,000
Series G Preferred Stock [Member]
Preferred Units [Line Items]
Noncontrolling Interest in Operating Partnerships	27,000,000	27,000,000
Preferred Units, Outstanding	540,000	540,000
Preferred Stock, Liquidation Preference	50	50
Preferred Stock, Dividend Rate		6.70%
Preferred Stock Redeemable As Of		Dec. 15, 2011
Preferred Stock, Exchangeable After		12/15/16 into Series G Cumulative Redeemable Preferred Shares of the Trust
Series H Preferred Stock [Member]
Preferred Units [Line Items]
Preferred Stock, Dividend Rate		7.40%
Preferred Unit Redemptions [Abstract]
Preferred Stock, Redemption Amount		100,000,000
Series B Preferred Stock [Member]
Preferred Units [Line Items]
Preferred Stock, Dividend Rate		7.45%
Preferred Unit Redemptions [Abstract]
Preferred Stock, Redemption Amount		$ 95,000,000