Note 12 - Other Accrued Liabilities - Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Subsidence Liability	$ 89,917	$ 90,645
Accrued Payroll and Benefits	20,444	21,102
Accrued Equipment Obligations	10,097	0
Accrued Interest	9,576	6,281
Other	22,004	21,034
Postretirement Benefits Other than Pensions	30,410	31,833
Asset Retirement Obligations	22,057	21,741
Operating Lease Liability	20,020	19,479
Pneumoconiosis Benefits	12,092	12,331
Workers' Compensation	10,778	11,323
Total Other Accrued Liabilities	$ 247,395	$ 235,769