v2.4.0.8
CWP and Workers Comp - Net Periodic Costs (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
Schedule of Net Periodic Benefit Costs and Assumptions for Defined Benefit Postretirement Plans [Line Items]        
Amortization of actuarial gain $ (23,559) $ (26,072) $ (48,747) $ (53,077)
Net periodic (benefit) cost 20,435 12,157 64,526 27,056
Coal Workers Pneumoconiosis [Member]
        
Schedule of Net Periodic Benefit Costs and Assumptions for Defined Benefit Postretirement Plans [Line Items]        
Service cost 2,135 1,928 4,270 3,856
Interest cost 1,808 1,991 3,616 3,982
Amortization of actuarial gain (4,212) (4,933) (8,425) (9,867)
State administrative fees and insurance bond premiums 0 0 0 0
Legal and administrative costs 0 0 0 0
Net periodic (benefit) cost (269) (1,014) (539) (2,029)
Payments for Coal Workers Pnenumoconiosis     5,372  
Workers Compensation [Member]
        
Schedule of Net Periodic Benefit Costs and Assumptions for Defined Benefit Postretirement Plans [Line Items]        
Service cost 3,533 3,634 7,066 7,268
Interest cost 1,655 1,778 3,310 3,556
Amortization of actuarial gain (699) (986) (1,398) (1,972)
State administrative fees and insurance bond premiums 1,345 1,635 3,004 3,545
Legal and administrative costs 591 648 1,182 1,296
Net periodic (benefit) cost 6,425 6,709 13,164 13,693
Payments for workers compensation benefits, state administrative fees and surety bond premiums     $ 14,946