Note 3 - Vessel Acquisitions and Dispositions (Details Textual) $ in Thousands, NOK in Millions	1 Months Ended				3 Months Ended			5 Months Ended		6 Months Ended		12 Months Ended
	Jan. 31, 2017 NOK	Jan. 31, 2017 USD ($)	Jul. 31, 2016	May 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	May 31, 2016 NOK	May 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015	Mar. 31, 2016 USD ($)
Vessel [Member] | North Sea [Member]
Proceeds from Sale of Property, Plant, and Equipment				$ 1,400
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property						$ (5,900)
Vessel [Member] | South East Asia [Member] | Subsequent Event [Member]
Proceeds from Sale of Property, Plant, and Equipment					$ 3,600
Vessel [Member] | South East Asia [Member]
Number of Vessels Sold			2
UNITED STATES
Number of Vessels, Remaining to be Delivered												2
NORWAY
Installment Payment on Vessel Contracts								NOK 92.2	$ 11,000
Final Payment on Vessel Contracts	NOK 195.0	$ 23,300
BAE Systems [Member]
Price of Vessels, Option or Right, Not Obligation to Purchase, Exercised													$ 26,000
Interest Costs Capitalized						$ 700	$ 1,300			$ 1,700	$ 2,500
Proceeds from Sale of Property, Plant, and Equipment										1,429	715
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property										$ (5,918)