Note 12 - Other Accrued Liabilities - Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Subsidence Liability	$ 89,554	$ 90,645
Accrued Payroll and Benefits	21,179	21,102
Accrued Other Taxes	7,126	4,753
Accrued Equipment Obligations	6,698	0
Accrued Interest	6,236	6,281
Other	23,845	16,281
Postretirement Benefits Other than Pensions	26,073	31,833
Asset Retirement Obligations	20,587	21,741
Pneumoconiosis Benefits	12,203	12,331
Workers' Compensation	9,653	11,323
Total Other Accrued Liabilities	243,395	235,769
Other Accrued Liabilities [Member]
Operating Lease Liability	$ 20,241	$ 19,479