Note 2 - Business Segments and Sales of Products (Details Textual) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Environmental Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 0.4		$ 0.9
Financially-settled Forward Contracts [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Derivative, Gain (Loss) on Derivative, Net, Total	$ 8.2	$ 11.3	$ 9.1	$ 6.6