Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Receivables, allowance	$ 1,057	$ 1,403
Accrued rental income, allowance	3,086	4,870
Accumulated amortization - debt costs	17,887	15,381
Unamortized premium - mortgages payable	202	0
Unamortized discount - notes payable - convertible	3,174	6,363
Unamortized discount - notes payable	$ 9,571	$ 5,033
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)		104,754,859
Common stock, shares issued and outstanding (in shares)	109,421,774	104,754,859
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 [Member]
Series D and Series C, depositary shares issued (in shares)	11,500,000	0
Series D and Series C, depositary shares outstanding (in shares)	11,500,000	0
Series D and Series C, stated liquidation value per share (in dollars per share)	$ 25	$ 0
Series C Depositary Share [Member]
Series D and Series C, depositary shares issued (in shares)	0	3,680,000
Series D and Series C, depositary shares outstanding (in shares)	0	3,680,000
Series D and Series C, stated liquidation value per share (in dollars per share)	$ 0	$ 25