CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Allowance on receivables	$ 506	$ 2,273
Allowance on accrued rental income	1,842	1,842
Accumulated amortization	$ 15,574	$ 14,118
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)	171,694,209	161,503,585
Common stock, shares outstanding (in shares)	171,694,209	161,503,585
5.700% Series E Preferred Stock, $0.01 par value
Preferred stock, issued (in shares)		115,000
Preferred stock, outstanding (in shares)		115,000
Stated liquidation value per share (in dollars per share)		$ 2,500
Dividend rate		5.70%
Depositary Shares, each representing one-hundredth of a share of 5.200% Series F Preferred Stock, $0.01 par value
Preferred stock, issued (in shares)	138,000	138,000
Preferred stock, outstanding (in shares)	138,000	138,000
Stated liquidation value per share (in dollars per share)	$ 2,500	$ 2,500
Dividend rate	5.20%	5.20%