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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Coal Workers Pneumoconiosis [Member]
Service Cost	$ 1,115	$ 1,151	$ 2,230	$ 2,302
Interest Cost	1,177	1,552	2,355	3,103
Amortization of Actuarial Loss	2,091	1,401	4,182	2,802
State Administrative Fees and Insurance Bond Premiums	0	0	0	0
Net Periodic Benefit (Credit) Cost	4,383	4,104	8,767	8,207
Workers Compensation [Member]
Service Cost	1,059	1,569	2,118	3,138
Interest Cost	282	461	564	922
Amortization of Actuarial Loss	(45)	(122)	(90)	(244)
State Administrative Fees and Insurance Bond Premiums	444	461	912	1,082
Net Periodic Benefit (Credit) Cost	$ 1,740	$ 2,369	$ 3,504	$ 4,898