WORKERS' COMPENSATION AND PNEUMOCONIOSIS (Details 2) - Pneumoconiosis benefits - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accrued Workers Compensation And Pneumoconiosis Benefits
Service cost		$ 732	$ 857	$ 1,464	$ 1,714
Interest cost		523	565	1,047	1,131
Amortization of net actuarial gain	[1]	(112)	(263)	(225)	(526)
Net periodic benefit cost		$ 1,143	$ 1,159	$ 2,286	$ 2,319

[1] Amortization of net actuarial gain is included in the operating expenses line item within our condensed consolidated statements of income.