OTHER ACCRUED LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Subsidence Liability	$ 108,313	$ 104,437
Accrued Payroll and Benefits	16,462	17,326
Equipment Lease Rental	13,163	15,286
Deferred Revenue	8,915	10,520
Accrued Other Taxes	8,765	12,732
Litigation	3,100	12,532
Short-Term Incentive Compensation	2,507	6,073
Other	14,836	21,986
Current Portion of Long-Term Liabilities:
Postretirement Benefits Other than Pensions	43,025	40,611
Asset Retirement Obligations	28,675	26,259
Workers' Compensation	12,280	13,596
Pneumoconiosis Benefits	9,004	10,763
Total Other Accrued Liabilities	$ 269,045	$ 292,121