ACCRUED WORKERS' COMPENSATION AND PNEUMOCONIOSIS BENEFITS (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accrued Workers Compensation And Pneumoconiosis Benefits
Total adjustments	$ (1,804)	$ (21,739)	$ (1,572)
Black Lung
Accrued Workers Compensation And Pneumoconiosis Benefits
Net actuarial gain (loss)	2,156	(4,570)	(6,872)
Reversal of amortization item, net actuarial (gain) loss	776	(223)	(176)
Total adjustments	$ 2,932	$ (4,793)	$ (7,048)