Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) $ in Thousands		12 Months Ended
	Jul. 10, 2022 employee	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Property, plant, and equipment
Less: accumulated depreciation, depletion, and amortization		$ (139,745)	$ (111,937)
Total property, plant and equipment, net		459,091	429,842
Idle mine costs		9,500
Plant and equipment
Property, plant, and equipment
Property, plant and equipment, gross		290,060	232,885
Mining property and mineral rights
Property, plant, and equipment
Property, plant and equipment, gross		120,532	120,760
Number of personnel in the mine | employee	0
Construction in process
Property, plant, and equipment
Property, plant and equipment, gross		13,984	34,698
Capitalized mine development costs
Property, plant, and equipment
Property, plant and equipment, gross		174,260	153,436
Coal Properties
Property, plant, and equipment
Capitalized amounts related to coal reserves		$ 17,400	$ 33,400