Note 8 - Revenue - Domestic Revenues an Export Revenues (Details) $ in Thousands, T in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) T	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) T $ / T	Jun. 30, 2021 USD ($)
REVENUES
Revenues	$ 138,655	$ 76,057	$ 293,537	$ 119,511
Term of domestic sales contracts			1 year
Domestic Coal Revenues
REVENUES
Revenues	91,397	37,550	$ 150,629	57,656
Export Revenues
REVENUES
Revenues	$ 47,258	$ 38,507	$ 142,908	$ 61,855
Fixed Priced Contracts
REVENUES
Outstanding performance obligation, mass | T	1.1		1.1
Average per ton | $ / T			196
Contracts with Indexed Based Pricing Mechanisms
REVENUES
Outstanding performance obligation, mass | T	0.2		0.2