Note 9 - Revenue - Domestic Revenues an Export Revenues (Details) $ in Thousands, T in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) T	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) T $ / T	Sep. 30, 2020 USD ($)
REVENUES
Revenues	$ 76,377	$ 39,459	$ 195,889	$ 117,769
Term of domestic sales contracts			1 year
Domestic Coal Revenues
REVENUES
Revenues	47,954	27,284	$ 105,611	89,795
Export Revenues
REVENUES
Revenues	$ 28,423	$ 12,175	$ 90,278	$ 27,974
Fixed Priced Contracts
REVENUES
Outstanding performance obligation, mass | T	0.5		0.5
Average per ton | $ / T			84
Contracts with Indexed Based Pricing Mechanisms
REVENUES
Outstanding performance obligation, mass | T	0.1		0.1