Note 4 - Vessel Acquisitions, Dispositions and New-build Program (Details Textual) $ in Thousands, kr in Millions	1 Months Ended			2 Months Ended	5 Months Ended		10 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Jan. 31, 2017 NOK (kr)	Jan. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	May 31, 2016 NOK (kr)	May 31, 2016 USD ($)	Nov. 14, 2017 USD ($)	Dec. 31, 2017	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2016 USD ($)
Proceeds from Sale of Property, Plant, and Equipment
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property
Number of Vessels Under Construction								0
NORWAY
Payments for Installment on Vessel Contracts		kr 195.0	$ 23,300
Predecessor [Member]
Proceeds from Sale of Property, Plant, and Equipment							$ 3,065		$ 6,529	$ 8,910
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property							$ (5,207)		(8,564)	$ (1,160)
Number of Vessels Under Construction										2
Predecessor [Member] | NORWAY
Payments for Installment on Vessel Contracts					kr 92.2	$ 11,000
Predecessor [Member] | BAE Systems [Member]
Price of Vessels, Option or Right, Not Obligation to Purchase, Exercised											$ 26,000
Predecessor [Member] | Vessel [Member]
Proceeds from Sale of Property, Plant, and Equipment									6,500
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property									$ (8,600)
Predecessor [Member] | Fast Supply Vessels [Member]
Number of Vessel Sold	2
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property	$ (5,300)
North Sea Segment [Member] | Predecessor [Member]
Number of Vessel Sold									1
Southeast Asia Segment [Member] | Predecessor [Member]
Number of Vessel Sold									3