CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Intangible assets, accumulated amortization	$ 19,896,000	$ 18,248,000
Preferred shares, par value (in dollars per share)	$ 0.01
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	79,490,000	77,550,000
Common stock, shares outstanding (in shares)	79,490,000	77,550,000
Series B Preferred Stock
Preferred shares, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred shares, authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	3,450,000	3,450,000
Preferred shares, outstanding (in shares)	3,450,000	3,450,000
Liquidation preference	$ 87,840,000	$ 86,250,000
Series C Preferred Stock
Preferred shares, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred shares, authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	6,900,000	6,900,000
Preferred shares, outstanding (in shares)	6,900,000	6,900,000
Liquidation preference	$ 175,605,000	$ 172,500,000
Series D Preferred Stock
Preferred shares, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred shares, authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	5,000,000	5,000,000
Preferred shares, outstanding (in shares)	5,000,000	5,000,000
Liquidation preference	$ 127,149,000	$ 125,000,000