Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Property, plant, and equipment
Less: accumulated depreciation, depletion, and amortization	$ (152,297)	$ (139,745)
Total property, plant and equipment, net	466,253	459,091
Plant and equipment
Property, plant, and equipment
Property, plant and equipment, gross	296,837	290,060
Mining property and mineral rights
Property, plant, and equipment
Property, plant and equipment, gross	120,532	120,532
Construction in process
Property, plant, and equipment
Property, plant and equipment, gross	23,010	13,984
Capitalized mine development costs
Property, plant, and equipment
Property, plant and equipment, gross	$ 178,171	$ 174,260