COMPONENTS OF COAL WORKERS’ PNEUMOCONIOSIS (CWP) AND WORKERS’ COMPENSATION NET PERIODIC BENEFIT COSTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Coal Workers Pneumoconiosis
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	$ 1,129	$ 1,041	$ 3,388	$ 3,285
Interest Cost	1,013	1,053	3,038	3,230
Amortization of Actuarial Gain	(1,908)	(1,188)	(5,724)	(3,759)
Administrative Fees	151	0	454	0
State Administrative Fees and Insurance Bond Premiums	0	0	0	0
Curtailment Gain	0	0	0	(1,307)
Net Periodic Benefit (Credit) Cost	385	906	1,156	1,449
Benefit claims paid			9,874
Workers Compensation
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	1,434	1,866	4,301	5,599
Interest Cost	580	625	1,740	1,875
Amortization of Actuarial Gain	(150)	(99)	(449)	(297)
Administrative Fees	135	776	405	2,441
State Administrative Fees and Insurance Bond Premiums	609	0	1,969	0
Curtailment Gain	0	0	0	0
Net Periodic Benefit (Credit) Cost	$ 2,608	$ 3,168	7,966	$ 9,618
Benefit claims paid			$ 10,074