Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Property, plant, and equipment
Less: accumulated depreciation, depletion, and amortization	$ (201,055)	$ (139,745)
Total property, plant and equipment, net	482,019	459,091
Plant and equipment
Property, plant, and equipment
Property, plant and equipment, gross	331,899	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	31,048	13,984
Capitalized mine development costs
Property, plant, and equipment
Property, plant and equipment, gross	199,595	174,260
Coal Properties
Property, plant, and equipment
Capitalized amounts related to coal reserves	$ 16,200	$ 17,400