Note 6 - Components of Coal Workers' Pneumoconiosis (CWP) and Workers' Compensation Net Periodic Benefit Costs - Components of Net Period Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Coal Workers Pneumoconiosis [Member]
Service Cost	$ 1,115	$ 1,150	$ 3,345	$ 3,452
Interest Cost	1,178	1,552	3,533	4,655
Amortization of Actuarial Loss	2,091	1,401	6,273	4,203
State Administrative Fees and Insurance Bond Premiums	0	0	0	0
Net Periodic Benefit (Credit) Cost	4,384	4,103	13,151	12,310
Workers Compensation [Member]
Service Cost	1,059	1,569	3,177	4,707
Interest Cost	282	461	846	1,383
Amortization of Actuarial Loss	(45)	(122)	(135)	(366)
State Administrative Fees and Insurance Bond Premiums	445	583	1,357	1,665
Net Periodic Benefit (Credit) Cost	$ 1,741	$ 2,491	$ 5,245	$ 7,389