CWP and Workers Comp - Net Periodic Costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule of Net Periodic Benefit Costs and Assumptions for Defined Benefit Postretirement Plans [Line Items]
Amortization of actuarial gain	$ (21,055)	$ (26,611)	$ (69,802)	$ (79,688)
Net periodic (benefit) cost	19,139	12,696	83,665	39,751
Coal Workers Pneumoconiosis [Member]
Schedule of Net Periodic Benefit Costs and Assumptions for Defined Benefit Postretirement Plans [Line Items]
Service cost	2,135	1,927	6,405	5,783
Interest cost	1,808	1,991	5,424	5,973
Amortization of actuarial gain	(4,213)	(4,933)	(12,638)	(14,799)
State administrative fees and insurance bond premiums	0	0	0	0
Legal and administrative costs	0	0	0	0
Net periodic (benefit) cost	(270)	(1,015)	(809)	(3,043)
Payments for Coal Workers Pnenumoconiosis			7,879
Workers Compensation [Member]
Schedule of Net Periodic Benefit Costs and Assumptions for Defined Benefit Postretirement Plans [Line Items]
Service cost	3,533	3,634	10,599	10,903
Interest cost	1,655	1,778	4,966	5,335
Amortization of actuarial gain	(699)	(986)	(2,098)	(2,958)
State administrative fees and insurance bond premiums	1,496	1,795	4,500	5,340
Legal and administrative costs	591	648	1,773	1,943
Net periodic (benefit) cost	6,576	6,869	19,740	20,563
Payments for workers compensation benefits, state administrative fees and surety bond premiums			$ 21,271