Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) $ in Thousands		12 Months Ended
	Jul. 10, 2022 employee	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Property, plant, and equipment
Less: Accumulated depreciation and amortization		$ (111,937)	$ (80,269)
Total property, plant and equipment, net		429,842	227,077
Idle mine costs		9,500
Number of personnel in the mine | employee	0
Plant and equipment
Property, plant, and equipment
Property, plant and equipment, gross		232,885	167,019
Mining property and mineral rights
Property, plant, and equipment
Property, plant and equipment, gross		120,760	26,064
Construction in process
Property, plant, and equipment
Property, plant and equipment, gross		34,698	9,972
Capitalized mine development costs
Property, plant, and equipment
Property, plant and equipment, gross		153,436	104,291
Coal Properties
Property, plant, and equipment
Capitalized amounts related to coal reserves		$ 33,400	$ 25,100