Noncontrolling Interests - Outstanding Cumulative Redeemable Preferred Units (Details) (USD $)			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Series E Preferred Stock [Member]	Mar. 31, 2013 Series F Preferred Stock [Member]	Mar. 31, 2013 Series G Preferred Stock [Member]
Preferred Units [Line Items]
Noncontrolling Interest in Operating Partnerships			$ 20,000,000	$ 17,500,000	$ 27,000,000
Preferred Units, Outstanding	1,290,000	1,290,000	400,000	350,000	540,000
Preferred Stock, Liquidation Preference			$ 50	$ 50	$ 50
Preferred Stock, Dividend Rate, Percentage			7.00%	6.65%	6.70%
Preferred Stock Redeemable As Of			Jun. 16, 2010	Jun. 30, 2010	Dec. 15, 2011
Preferred Stock, Exchangeable After			6/16/15 into Series E Cumulative Redeemable Preferred Shares of the Trust	12/12/15 into Series F Cumulative Redeemable Preferred Shares of the Trust	12/15/16 into Series G Cumulative Redeemable Preferred Shares of the Trust