Note 3 - Property, Plant and Equipment - Depreciation and amortization (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Property, Plant and Equipment.
Capitalized Costs Related to Coal Reserves	$ 28,400		$ 28,400		$ 25,100
Depreciation of plant and equipment	5,346	$ 4,471	10,100	$ 8,870
Depreciation of right of use assets	1,383	127	2,097	127
Amortization of capitalized mine development costs	3,054	1,357	6,266	3,113
Total depreciation and amortization	$ 9,783	$ 5,955	$ 18,463	$ 12,110