Unaudited Condensed Consolidated Balance Sheets (Parentheticals) - USD ($) shares in Thousands, $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Allowance for doubtful accounts of trade accounts receivable	$ 1,023	$ 3,470
Accumulated depreciation of vessels, equipment, and other fixed assets	$ 21,360	$ 4,392
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000	5,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	25,000	25,000
Common stock, shares issued (in shares)	7,460	7,043
Common stock, shares outstanding (in shares)	7,458	7,042