Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Series E Depositary Share	Dec. 31, 2012 Series E Depositary Share	Dec. 31, 2013 Series D Depositary Share	Dec. 31, 2012 Series D Depositary Share
Receivables, net of allowance of $2,822 and $855, respectively	$ 2,822	$ 855
Accrued rental income, net of allowance of $3,181 and $3,270, respectively	3,181	3,270
Debt costs, net of accumulated amortization of $20,213 and $17,965, respectively	20,213	17,965
Mortgages payable, including unamortized premium of $130 and $187, respectively	130	187
Notes payable – convertible, net of unamortized discount of $2,072 at December 31, 2012	0	2,072
Notes payable, net of unamortized discount of $10,816 and $9,338, respectively	$ 10,816	$ 9,338
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	15,000,000	15,000,000
Depositary shares issued			11,500,000		11,500,000	11,500,000
Depositary shares outstanding			11,500,000		11,500,000	11,500,000
Stated liquidation value per share			$ 25.00		$ 25.00	$ 25
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	375,000,000	375,000,000
Common stock, shares issued	121,991,677	121,991,677
Common stock, shares issued and outstanding	111,554,997	111,554,997
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