Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Mortgages, notes and accrued interest receivable, allowance	$ 8		$ 5
Receivables allowance	671		566
Accrued rental income allowance	3,133		3,078
Debt costs accumulated amortization	$ 10,218		$ 9,877
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)	143,235,896		141,007,725
Common stock, shares outstanding (in shares)	143,235,896		141,007,425
Series D Depositary Share
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 Depositary Share
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