Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Property, plant, and equipment
Less: Accumulated depreciation and amortization	$ (80,269,000)	$ (56,242,000)
Total property, plant and equipment, net	227,077,000	180,531,000
Plant and Equipment
Property, plant, and equipment
Property, plant and equipment, gross	167,019,000	155,173,000
Mining Properties and Mineral Rights
Property, plant, and equipment
Property, plant and equipment, gross	26,064,000	76,000
Construction in Progress
Property, plant, and equipment
Property, plant and equipment, gross	9,972,000	7,245,000
Capitalized mine development cost
Property, plant, and equipment
Property, plant and equipment, gross	104,291,000	74,279,000
Coal Properties
Property, plant, and equipment
Capitalized Costs Related to Coal Reserves	$ 25,100,000	$ 15,400,000