Note 8 - Revenue - Domestic Revenues an Export Revenues (Details) $ in Thousands, T in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($) T	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) T $ / T	Sep. 30, 2021 USD ($)	Dec. 31, 2023 T $ / T
REVENUES
Revenues | $	$ 136,925	$ 76,377	$ 430,461	$ 195,889
Term of domestic sales contracts			1 year
Domestic Coal Revenues
REVENUES
Revenues | $	78,442	47,954	$ 231,365	105,611
Export Revenues
REVENUES
Revenues | $	$ 58,483	$ 28,423	$ 199,096	$ 90,278
Fixed Priced Contracts
REVENUES
Outstanding performance obligation, mass	0.5		0.5
Average per ton | $ / T			197
Fixed Priced Contracts | Forecast
REVENUES
Outstanding performance obligation, mass					1.4
Average per ton | $ / T					198
Contracts with Indexed Based Pricing Mechanisms
REVENUES
Outstanding performance obligation, mass	0.3		0.3
Contracts with Indexed Based Pricing Mechanisms | Forecast
REVENUES
Outstanding performance obligation, mass					0.1