Note 6 - Components of Coal Worker's Pneumoniosis (CWP) and Workers' Compensation Net Periodic Benefit Costs - Components of Net Period Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Coal Workers Pneumoconiosis [Member]
Service Cost	$ 1,115	$ 1,151
Interest Cost	1,178	1,551
Amortization of Actuarial Loss	2,091	1,401
State Administrative Fees and Insurance Bond Premiums	0	0
Net Periodic Benefit (Credit) Cost	4,384	4,103
Workers Compensation [Member]
Service Cost	1,059	1,569
Interest Cost	282	461
Amortization of Actuarial Loss	(45)	(122)
State Administrative Fees and Insurance Bond Premiums	468	621
Net Periodic Benefit (Credit) Cost	$ 1,764	$ 2,529