Consolidated Balance Sheets [Parenthetical] - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Convertible preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Convertible preferred stock, shares authorized	5,000,000	5,000,000
Convertible preferred stock, shares issued	0	0
Convertible preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	170,000,000	170,000,000
Common stock, shares issued	69,901,625	60,276,119
Treasury stock, shares held	79,545	79,545