WORKERS' COMPENSATION AND PNEUMOCONIOSIS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reconciliation of the changes in workers' compensation liability
Beginning balance	$ 78,755	$ 76,902	$ 77,046	$ 73,201
Accruals increase	3,982	6,291	7,947	12,214
Payments	(2,727)	(2,683)	(5,603)	(5,589)
Interest accretion	620	685	1,240	1,369
Ending balance	$ 80,630	$ 81,195	$ 80,630	$ 81,195