Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Receivables allowance	$ 3,097,000	$ 2,822,000
Accrued rental income allowance	3,086,000	3,181,000
Debt costs accumulated amortization	12,924,000	20,213,000
Unamortized premium - mortgages payable	101,000	130,000
Unamortized discount - notes payable	$ 10,909,000	$ 10,816,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	15,000,000	15,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	375,000,000	375,000,000
Common stock, shares issued (in shares)	124,510,923	121,991,677
Common stock, shares outstanding (in shares)	124,510,923	121,991,677
Excess stock, par value (in dollars per share)	$ 0.01	$ 0.01
Excess stock, shares authorized (in shares)	390,000,000	390,000,000
Excess stock, shares issued (in shares)	0	0
Excess stock, shares outstanding (in shares)	0	0
Series D Depositary Share
Series D and E, depositary shares issued (in shares)	11,500,000	11,500,000
Series D and E, depositary shares outstanding (in shares)	11,500,000	11,500,000
Series D and E, stated liquidation value per share (in dollars per share)	$ 25	$ 25
Series E Depositary Share
Series D and E, depositary shares issued (in shares)	11,500,000	11,500,000
Series D and E, depositary shares outstanding (in shares)	11,500,000	11,500,000
Series D and E, stated liquidation value per share (in dollars per share)	$ 25	$ 25