Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Property, plant, and equipment
Less: accumulated depreciation, depletion, and amortization	$ (184,290)	$ (139,745)
Total property, plant and equipment, net	476,748	459,091
Capitalized amounts related to coal reserves	1,600
Accrued loss recovery asset	3,100
Plant and equipment
Property, plant, and equipment
Property, plant and equipment, gross	323,440	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	30,223	13,984
Capitalized mine development costs
Property, plant, and equipment
Property, plant and equipment, gross	186,843	174,260
Proceeds from insurance for methane ignition on mine	6,000
Increase in property, plant, and equipment and noncurrent liabilities due to change in asset retirement obligations estimates	$ 1,600
Gain on Insurance Recovery		$ 4,900
Accrued loss recovery asset			$ 1,100