Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Allowance on receivables	$ 1,784	$ 2,822
Allowance on accrued rental income	3,086	3,181
Accumulated amortization on debt costs	14,353	20,213
Unamortized premium on mortgages payable	890	130
Unamortized discount on notes payable	$ 10,285	$ 10,816
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	15,000,000	15,000,000
Stated liquidation value per share (in dollars per share)	$ 25.00
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	375,000,000	375,000,000
Common stock, shares issued	132,010,104	121,991,677
Common stock, shares issued and outstanding	132,010,104	121,991,677
Excess stock, par value (in dollars per share)	$ 0.01	$ 0.01
Excess stock, shares authorized	390,000,000	390,000,000
Excess stock, shares issued	0	0
Excess stock, shares outstanding	0	0
Series D Preferred Stock
Depositary shares issued	115,000	115,000
Depositary shares outstanding	115,000	115,000
Stated liquidation value per share (in dollars per share)	$ 2,500.00	$ 2,500.00
Dividend Rate	6.625%	6.625%
Series E Preferred Stock
Depositary shares issued	115,000	115,000
Depositary shares outstanding	115,000	115,000
Stated liquidation value per share (in dollars per share)	$ 2,500.00	$ 2,500.00
Dividend Rate	5.70%	5.70%