Derivative and Other Fair Value Instruments (Details Textuals) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Secured Debt	$ 3,948,115,000	$ 4,111,487,000
Unsecured Debt	5,400,000,000
Notes, net	5,354,038,000	5,609,574,000
Fair value of mortgage notes payable	4,300,000,000	4,300,000,000
Fair value of unsecured notes payable including line of credit	6,000,000,000	6,000,000,000
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	(199,000,000)	(197,600,000)
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 19,100,000