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ACCRUED WORKERS' COMPENSATION AND PNEUMOCONIOSIS BENEFITS (Details 2) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Accrued Workers Compensation And Pneumoconiosis Benefits      
Workers' compensation (benefit) expense $ (110) $ 17,572 $ 18,996
Total expense 6,623 24,478 24,500
Black Lung
     
Accrued Workers Compensation And Pneumoconiosis Benefits      
Service cost 3,810 3,758 3,345
Interest cost 2,253 2,372 2,382
Net amortization 670 776 (223)
Net periodic benefit cost $ 6,733 $ 6,906 $ 5,504