Note 12 - Other Accrued Liabilities - Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Subsidence Liability	$ 91,432	$ 89,554
Accrued Payroll and Benefits	23,185	21,179
Accrued Interest	8,985	6,236
Litigation	8,457	3,625
Accrued Other Taxes	5,267	7,126
Accrued Equipment Obligations	300	6,698
Other	20,319	20,220
Postretirement Benefits Other than Pensions	25,867	26,073
Asset Retirement Obligations	20,587	20,587
Pneumoconiosis Benefits	12,133	12,203
Workers' Compensation	9,683	9,653
Total Other Accrued Liabilities	245,755	243,395
Other Accrued Liabilities [Member]
Operating Lease Liability	$ 19,540	$ 20,241