Note 16 - Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Changes in Benefit Obligation, Plan Assets and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Salary Retirement (Note 15)	$ 38,947	$ 0
Coal Workers Pneumoconiosis [Member]
Benefit obligation at beginning of period	241,923	214,473
State administrative fees and insurance bond premiums	0	0	$ 0
Service cost	4,460	4,603	3,791
Interest cost	4,710	6,206	7,001
Actuarial (gain) loss	(22,256)	29,510
Benefits and other payments	(12,966)	(12,869)
Benefit obligation at end of period	215,871	241,923	214,473
Salary Retirement (Note 15)	0	0
Current liabilities	(12,398)	(12,203)
Noncurrent liabilities	(203,473)	(229,720)
Net asset (obligation) recognized	(215,871)	(241,923)
Net actuarial loss	40,638	71,259
Net amount recognized (before tax effect)	40,638	71,259
Workers Compensation [Member]
Benefit obligation at beginning of period	73,441	71,480
State administrative fees and insurance bond premiums	1,778	1,996	2,157
Service cost	4,236	6,276	5,685
Interest cost	1,127	1,844	2,585
Actuarial (gain) loss	(2,039)	1,897
Benefits and other payments	(11,282)	(10,052)
Benefit obligation at end of period	67,261	73,441	$ 71,480
Salary Retirement (Note 15)	1,092	602
Current liabilities	(10,205)	(9,653)
Noncurrent liabilities	(58,148)	(64,390)
Net asset (obligation) recognized	(67,261)	(73,441)
Net actuarial loss	(10,726)	(8,866)
Net amount recognized (before tax effect)	$ (10,726)	$ (8,866)