Note 2 - Business Segments and Sales of Products (Details Textual) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
Environmental Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 0.5
Financially-settled Forward Contracts [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Derivative, Gain (Loss) on Derivative, Net, Total	$ 0.9	$ (4.8)

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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+ Details