Note 8 - Revenue - Domestic Revenues an Export Revenues (Details) $ in Thousands, T in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($) T	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) T $ / T	Jun. 30, 2022 USD ($)
REVENUES
Revenues	$ 137,469	$ 138,655	$ 303,829	$ 293,537
Term of domestic sales contracts			1 year
Domestic Coal Revenues
REVENUES
Revenues	53,401	91,397	$ 93,428	150,629
Export Revenues
REVENUES
Revenues	$ 84,068	$ 47,258	$ 210,401	$ 142,908
Fixed Priced Contracts
REVENUES
Outstanding performance obligation, mass | T	0.9		0.9
Average per ton | $ / T			198
Contracts with Indexed Based Pricing Mechanisms
REVENUES
Outstanding performance obligation, mass | T	0.7		0.7