Note 8 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating loss	$ 26,570	$ 32,659
Valuation allowance	(3,681)	(4,651)
Stock-based compensation	163	0
Other	471	0
Total deferred tax assets	23,523	28,008
Coal properties	(26,446)	(30,368)
Investment in partnerships	(1,480)	(484)
Other	(203)	(6)
Total deferred tax liabilities	(28,129)	(30,858)
Net deferred tax liability	$ (4,606)	$ (2,850)