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Note 2 - Discontinued Operations (Details Textual) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent, Total						$ 18	$ (9)	$ (10)		$ (1)
Short-term Lease, Cost									20	136
Fuel Conversion Segment [Member] \| Discontinued Operations [Member]
Proceeds from Divestiture of Businesses, Net of Cash Divested, Total										505
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Total										20
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent, Total									$ 0	(1)
Fuel Conversion Segment [Member] \| Discontinued Operations, Disposed of by Sale [Member]
Short-term Lease, Cost										$ 21