Note 9 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Long-term deferred tax assets:
Net operating loss	$ 24,081	$ 18,956
Valuation allowance	(1,275)	0
Interest limitation carryforward	0	1,801
Capital loss carryforward	525	555
Alternative minimum tax credit	0	524
Stock-based compensation	179	135
Other	529	1,029
Total long-term deferred tax assets:	24,039	23,000
Coal properties	(26,863)	(27,884)
Net deferred tax liability	$ (2,824)	$ (4,884)