Note 4 - Vessel Acquisitions, Dispositions and New-build Program (Details Textual) $ in Thousands, NOK in Millions		1 Months Ended		5 Months Ended		12 Months Ended
	Mar. 15, 2017 USD ($)	Jan. 31, 2017 NOK	Jan. 31, 2017 USD ($)	May 31, 2016 NOK	May 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2016 USD ($)
Proceeds from Sale of Property, Plant, and Equipment						$ 6,529	$ 8,910	$ 32,261
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property						(8,564)	$ (1,160)	$ 12,461
Number of Vessels Under Construction							2
NORWAY
Payments for Installment on Vessel Contracts				NOK 92.2	$ 11,000
BAE Systems [Member]
Price of Vessels, Option or Right, Not Obligation to Purchase, Exercised									$ 26,000
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)
Crew Boat and Fast Supply Vessel [Member] | Subsequent Event [Member]
Number of Vessel Sold	2
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property	$ (5,300)
Platform Supply Vessel[ Member] | Subsequent Event [Member] | North Sea [Member]
Payments for Installment on Vessel Contracts		NOK 195.0	$ 23,300
North Sea Segment [Member]
Number of Vessel Sold						1
Southeast Asia Segment [Member]
Number of Vessel Sold						3