CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Intangible assets, accumulated amortization	$ 16,391,000	$ 15,543,000
Preferred shares, par value (in dollars per share)	$ 0.01
Common stock, par value (in dollars per share)	$ 1	$ 1.00
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	77,383,000	70,495,000
Common stock, shares outstanding (in shares)	77,383,000	70,495,000
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	$ 86,250,000	$ 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	$ 172,500,000	$ 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	$ 125,000,000	$ 125,000,000