Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Series C Depositary Share [Member]	Dec. 31, 2011 Series C Depositary Share [Member]	Dec. 31, 2012 Series D Depositary Share [Member]	Dec. 31, 2011 Series D Depositary Share [Member]
Receivables, allowance	$ 855	$ 1,403
Accrued rental income allowance	3,270	4,870
Accumulated amortization - debt costs	17,965	15,381
Unamortized premium - mortgages payable	187	0
Unamortized discount - notes payable - convertible	2,072	6,363
Unamortized discount - notes payable	$ 9,338	$ 5,033
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	15,000,000	15,000,000
Depositary shares issued			0	3,680,000	11,500,000	0
Depositary shares outstanding			0	3,680,000	11,500,000	0
Stated liquidation value per share			$ 0	$ 25	$ 25	$ 0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	375,000,000	375,000,000
Common stock, shares issued	111,554,997	104,754,859
Common stock, shares issued and outstanding	111,554,997	104,754,859
Excess stock, par value	$ 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