Note 5 - 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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Coal Workers Pneumoconiosis [Member]
Service Cost	$ 1,151	$ 948	$ 2,302	$ 1,896
Interest Cost	1,552	1,750	3,103	3,500
Amortization of Actuarial Loss	1,401	254	2,802	508
State Administrative Fees and Insurance Bond Premiums	0	0	0	0
Net Periodic Benefit (Credit) Cost	4,104	2,952	8,207	5,904
Workers Compensation [Member]
Service Cost	1,569	1,421	3,138	2,842
Interest Cost	461	646	922	1,293
Amortization of Actuarial Loss	(122)	(193)	(244)	(387)
State Administrative Fees and Insurance Bond Premiums	461	574	1,082	1,161
Net Periodic Benefit (Credit) Cost	$ 2,369	$ 2,448	$ 4,898	$ 4,909