Note 11 - Other Accrued Liabilities - Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Subsidence Liability	$ 90,849	$ 90,645
Accrued Payroll and Benefits	19,142	21,102
Accrued Equipment Obligations	6,550	0
Accrued Interest	5,737	6,281
Other	22,340	21,034
Postretirement Benefits Other than Pensions	30,884	31,833
Asset Retirement Obligations	22,057	21,741
Operating Lease Liability	19,790	19,479
Pneumoconiosis Benefits	12,172	12,331
Workers' Compensation	11,005	11,323
Total Other Accrued Liabilities	$ 240,526	$ 235,769