Note 16 - Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Coal Workers Pneumoconiosis [Member]
Service cost	$ 4,460	$ 4,603	$ 3,791
Interest cost	4,710	6,206	7,001
Recognized net actuarial loss (gain)	8,364	5,604	1,016
State administrative fees and insurance bond premiums	0	0	0
Net periodic benefit costs	17,534	16,413	11,808
Workers Compensation [Member]
Service cost	4,236	6,276	5,685
Interest cost	1,127	1,844	2,585
Recognized net actuarial loss (gain)	(179)	(488)	(774)
State administrative fees and insurance bond premiums	1,778	1,996	2,157
Net periodic benefit costs	$ 6,962	$ 9,628	$ 9,653