Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Receivables allowance	$ 1,887	$ 1,784
Accrued rental income allowance	3,086	3,086
Debt costs accumulated amortization	13,787	14,353
Unamortized premium - mortgages payable	839	890
Unamortized discount - notes payable	$ 9,968	$ 10,285
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)	133,446,857	132,010,104
Common stock, shares outstanding (in shares)	133,446,857	132,010,104
Series D
Dividend rate	6.625%	6.625%
Preferred stock, depositary shares issued (in shares)	115,000	115,000
Preferred stock, depositary shares outstanding (in shares)	115,000	115,000
Preferred stock, stated liquidation value per share (in dollars per share)	$ 2,500	$ 2,500
Series E
Dividend rate	5.70%	5.70%
Preferred stock, depositary shares issued (in shares)	115,000	115,000
Preferred stock, depositary shares outstanding (in shares)	115,000	115,000
Preferred stock, stated liquidation value per share (in dollars per share)	$ 2,500	$ 2,500