Noncontrolling Interests - Outstanding Cumulative Redeemable Preferred Units (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Preferred Units [Line Items]
Preferred Units, Outstanding	1,290,000	9,740,000
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
Preferred Units, Outstanding	400,000
Preferred Stock, Liquidation Preference	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
Preferred Units, Outstanding	350,000
Preferred Stock, Liquidation Preference	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
Preferred Units, Outstanding	540,000
Preferred Stock, Liquidation Preference	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