CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Mortgage and notes receivable allowance	$ 14	$ 5
Allowance on receivables	1,006	566
Allowance on accrued rental income	3,078	3,078
Accumulated amortization	$ 11,268	$ 9,877
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	15,000,000	15,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	375,000,000	375,000,000
Common stock, shares issued	147,149,945	147,149,945
Common stock, shares issued and outstanding	141,007,725	141,007,725
Series D Preferred Stock
Depositary shares issued (in shares)	115,000	115,000
Depositary shares outstanding (in shares)	115,000	115,000
Stated liquidation value per share (in dollars per share)	$ 2,500	$ 2,500
Dividend rate (percent)	6.625%	6.625%
Series E Preferred Stock
Depositary shares issued (in shares)	115,000	115,000
Depositary shares outstanding (in shares)	115,000	115,000
Stated liquidation value per share (in dollars per share)	$ 2,500	$ 2,500
Dividend rate (percent)	5.70%	5.70%
Series F Preferred Stock
Depositary shares issued (in shares)	138,000	0
Depositary shares outstanding (in shares)	138,000	0
Stated liquidation value per share (in dollars per share)	$ 2,500	$ 0
Dividend rate (percent)	5.20%	0.00%