ACCRUED WORKERS' COMPENSATION AND PNEUMOCONIOSIS BENEFITS (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of the changes in workers' compensation liability
Balance at the beginning of the period	$ 77,046	$ 73,201
Accruals	18,544	24,812
Payments	(10,639)	(10,477)
Interest accretion	2,481	2,739
Valuation gain	(24,523)	(13,229)
Balance at the end of the period	$ 62,909	$ 77,046