Note 8 - Subsequent Event (Details Textual) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2018 USD ($) $ / shares	Jun. 30, 2018 $ / shares	Dec. 31, 2017 $ / shares
Common Stock, Par or Stated Value Per Share | $ / shares		$ 0.01	$ 0.01
Scenario, Forecast [Member] | Tidewater Inc. [Member]
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.001
Scenario, Forecast [Member] | Gulfmark Offshore, Inc. [Member] | Tidewater Inc. [Member]
Business Combination Exchange Ratio	1.1
Business Combination, Termination Fee, Acquiror | $	$ 35
Business Combination, Termination Fee, Acquiree | $	$ 13