CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (UNAUDITED) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
CONDENSED CONSOLIDATED BALANCE SHEETS
Vessels, accumulated depreciation	$ 239,136	$ 221,646
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares	225,000,000	225,000,000
Common stock, issued shares	83,267,426	83,267,426
Common stock, outstanding shares	83,267,426	83,267,426
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred Stock, Shares Issued	0	0
Preferred stock, outstanding shares	0	0