Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Property, plant, and equipment
Less: accumulated depreciation, depletion, and amortization	$ (222,448)	$ (201,055)
Total property, plant and equipment, net	487,872	482,019
Plant and equipment
Property, plant, and equipment
Property, plant and equipment, gross	367,108	331,899
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	12,316	31,048
Capitalized mine development costs
Property, plant, and equipment
Property, plant and equipment, gross	$ 210,364	$ 199,595