CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Allowance on receivables	$ 835	$ 506
Allowance on accrued rental income	6,947	1,842
Debt costs, accumulated amortization	$ 17,294	$ 15,574
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)	175,232,971	171,694,209
Common stock, shares outstanding (in shares)	175,232,971	171,694,209
5.200% Series F, 138,000 shares issued and outstanding, at stated liquidation value of $2,500 per share
Dividend rate	5.20%	5.20%
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