Note 6 - Discontinued Operations and Assets and Liabilities Held for Sale (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2020
Goodwill, Impairment Loss		$ 0	$ 0	$ 1,389
Impairment of Long-Lived Assets to be Disposed of	$ 1,300	1,259	23,427	$ 0
Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of			17,600
Corrosion Protection [Member]
Impairment of Long-Lived Assets to be Disposed of			2,900
Corporate Segment [Member]
Impairment of Long-Lived Assets to be Disposed of			$ 2,900
Energy Services [Member] | Discontinued Operations, Held-for-sale [Member]
Goodwill, Impairment Loss	$ 7,300
Energy Services [Member] | Discontinued Operations, Held-for-sale [Member] | Minimum [Member]
Disposal Group, Including Discontinued Operation, Divestiture Costs		2,000
Energy Services [Member] | Discontinued Operations, Held-for-sale [Member] | Maximum [Member]
Disposal Group, Including Discontinued Operation, Divestiture Costs		$ 3,000
Energy Services [Member] | Weighted Average Cost of Capital [Member] | Discontinued Operations, Held-for-sale [Member]
Goodwill, Measurement Input	0.170	0.170			0.150