Subsequent Events/Other (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Debt Instrument [Line Items]
Convertible Notes, stated interest rate	6.95%		6.95%
Maturity date description			October 5,2012
Unsecured revolving credit facility	$ 1,425,000,000		$ 1,425,000,000
Amount available on the credit facility	1,340,000,000		1,340,000,000
Subsequent Events/Other (Textuals) [Abstract]
Repayment of mortgage loans			176,300,000
Number Of Properties Disposed Of			2
Number of apartment units sold			685
Value of property sold			66,500,000
Percentage of facility fee paid by the company			0.20%
Interest rate description			LIBOR plus a spread (currently 1.15%)
Acquisition of properties			3,800,000	4,000,000
Write-off of pursuit costs			3,038,000	2,062,000
Other expenses	(4,626,000)	(1,643,000)	(6,790,000)	(6,026,000)
Insurance/Litigation Settlement proceeds				5,200,000
Estimates of lost revenue and garage reconstruction					14,000,000
Estimates Of Lost Revenue And Garage Reconstruction After Insurance Reimbursements					8,000,000
Initial insurance proceeds			1,600,000
Real estate tax and insurance			1,300,000
Net gain on the sale			1,000,000
Sale price of disposed corporate housing business			4,000,000
Loan amount provided to the buyer by the company			2,000,000
3.85% Unsecured Debt [Member]
Debt Instrument [Line Items]
Convertible Notes, stated interest rate	3.85%		3.85%
Maturity date description			final maturity of 2026
Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maturity date description			July 13, 2014
Unsecured revolving credit facility	1,250,000,000		1,250,000,000
Amount available on the credit facility	$ 1,170,000,000		$ 1,170,000,000