Equity, Capital and other Interests (Details Textuals) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2011 Year Project Apartment Property Store Customers OptionPlan State MilitaryHouse	Sep. 30, 2010	Dec. 31, 2009	Jun. 16, 2011	Dec. 31, 2010
Class of Stock [Line Items]
Common shares added to ATM program	5,700,000
Authorization to issue additional common shares	10,000,000
Acquired all of its partner's interest in 1,351 partially owned units	1,351
Reduction of paid in capital	$ 4,800,000
Reduction in partially owned properties	8,000,000
Partially owned development projects acquired from outside partner	3
Shares repurchased	0
Business Acquisition [Line Items]
Cost of acquiring properties	731,948,000
Equity, Capital and Other Interests (Textuals) [Abstract]
Basis for exchange units in operating partnerships of noncontrolling interest	one for one basis
Redemption value of approximately $378.8 million	378,798,000				383,540,000
100,000,000 authorized preferred shares	100,000,000				100,000,000
Preferred stock par value per share	$ 0.01				$ 0.01
Annual dividend of $1.62 per share	$ 1.62
Basis for exchangeable limited partnership units		one for one basis
Depository shares in relation to Preferred shares	ten times
May sell up to 17.0 million Common Shares			17,000,000
Years Company can trade existing Common Shares in market at current prices as well as through negotiated transactions			3 years
Basis for exchangeable operating partnerships units			One-for-one common Share per OP Unit basis
Number of shares authorized for issuance under 2011 plan				12,980,741
Authorized $464.6 million to be repurchased	464,600,000
Value of depository shares in relation to liquidation value and dividend per share	0.1
OPERATING PARTNERSHIP
Class of Stock [Line Items]
Common Stock issued during period, shares	3,000,000
Common Shares average price for total consideration through the ATM program	$ 50.84
Total consideration through ATM program	154,500,000
OP units issued by operating partnership	3,000,000
Depository units in relation to Preference Units	ten times
Annual dividend of $1.62 per Unit	$ 1.62
Value of depository units in relation to liquidation value and dividend per unit	0.1
Business Acquisition [Line Items]
Redemption value of approximately $378.8 million	378,800,000
Partially Owned Properties acquired [Member]
Business Acquisition [Line Items]
Cost of acquiring properties	$ 12,800,000