OTHER ACCRUED LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Subsidence Liability	$ 93,202	$ 83,532
Accrued Payroll and Benefits	17,144	12,978
Accrued Interest	11,521	6,850
Accrued Other Taxes	3,357	5,050
Litigation	2,640	8,235
Short-Term Incentive Compensation	2,411	6,024
Other	10,167	15,588
Current Portion of Long-Term Liabilities:
Postretirement Benefits Other than Pensions	32,361	32,345
Asset Retirement Obligations	29,413	31,017
Operating Lease Liability	15,769
Workers' Compensation	11,846	12,628
Pneumoconiosis Benefits	10,786	12,187
Total Other Accrued Liabilities	$ 240,617	$ 226,434