Summary of Significant Accounting Policies (Details) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2011 Year Project Apartment Property Store Customers OptionPlan State MilitaryHouse	Sep. 30, 2010	Dec. 31, 2011	Dec. 31, 2008	Aug. 18, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Unsecured Notes, face amount	$ 650,000,000
Convertible Notes, Premiums paid	0
Convertible Notes, stated interest rate	6.95%
Summary of Significant Accounting Policies (Textuals) [Abstract]
Deferred Tax Asset	38,700,000
Partially Owned Consolidated Properties	21
Partially Owned Consolidated Units	3,916
Noncontrolling Interests - Partially Owned Properties	(1,714,000)					7,991,000
Company owned properties in limited-life partnerships	6
Noncontrolling Interest Settlement Value	32,900,000
Convertible Notes, outstanding	482,500,000				482,500,000
Reduction in Earnings	5,000,000	5,800,000	5,000,000
Amount of Conversion Option	44,300,000
Paid-In Capital Increase				44,300,000
Decrease in Balance of Notes				17,300,000
Decrease in Earnings Per Share	$ 0.02	$ 0.02	$ 0.02
Unamortized cash and conversion option discounts	0					5,000,000
Carrying amount of conversion option remaining in paid-in capital	44,300,000					44,300,000
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Unsecured Notes, face amount	650,000,000
Convertible Notes, Premiums paid	0
Convertible Notes, issuance date	August 2006
Convertible Notes, maturity date	Aug. 01, 2026
Convertible Notes, stated interest rate	3.85%	3.85%
Interest expense recognized in relation to nonconvertible debt	11,800,000	13,900,000
Effective interest rate for conversion option	5.80%
Adjustments for New Accounting Pronouncement [Member] | Restatement Adjustment [Member]
Retained Earnings Adjustments [Line Items]
Retained Earnings Decrease				$ 27,000,000