Note 3 - Property, Plant and Equipment - Depreciation and amortization (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Property, Plant and Equipment.
Capitalized Costs Related to Coal Reserves	$ 46,200		$ 46,200		$ 25,100
Depreciation of plant and equipment	6,763	$ 4,484	16,864	$ 13,354
Depreciation of right of use assets	1,710	413	3,806	540
Amortization of capitalized mine development costs	2,962	1,854	9,228	4,967
Total depreciation and amortization	$ 11,435	$ 6,751	$ 29,898	$ 18,861