Note 3 - Property, Plant and Equipment - Depreciation and amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment.
Depreciation of plant and equipment	$ 24,132	$ 17,945	$ 17,094
Amortization of right of use assets (finance leases)	4,846	1,109
Amortization and depletion of capitalized mine development costs and mineral rights	12,216	7,151	3,818
Total depreciation and amortization	$ 41,194	$ 26,205	$ 20,912