CWP and Workers Comp (Details) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2011	Sep. 30, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Deferred Income Tax Expense (Benefit)				$ (53,011,000)	$ 17,029,000	$ 47,430,000
Coal Workers Pneumoconiosis [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	4,620,000				5,067,000	7,074,000
Interest cost	9,330,000			9,330,000	10,789,000	12,054,000
Post Employment Benefit Plan Legal And Administrative Costs				3,000,000	3,000,000	2,700,000
Amortization of actuarial gain	21,182,000				21,585,000	19,590,000
State administrative fees and insurance bond premiums	0			0	0	0
Legal and administrative costs				7,620,000	8,067,000
Net periodic (benefit) cost	(4,960,000)	(3,457,000)		1,510,000
Legal and administrative costs				7,620,000	8,067,000
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	183,580,000			183,580,000	184,531,000	194,641,000
Defined Benefit Plan, Actuarial Net (Gains) Losses				(6,783,000)	(17,381,000)
Defined Benefit Plan, Benefits Paid				(11,118,000)	(11,585,000)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	173,553,000			173,553,000	(173,616,000)
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(183,580,000)			(183,580,000)	(184,531,000)
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	(10,027,000)			(10,027,000)	(10,915,000)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(164,374,000)			(164,374,000)	(178,772,000)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax	(395,000)			(395,000)	(1,123,000)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(164,769,000)			(164,769,000)	(179,895,000)
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Defined Benefit Plan, Amortization of Net Gains (Losses)			(19,338,000)
Defined Benefit Plan, Amortization of Net Prior Service Cost (Credit)	(728,000)		(395,000)		(728,000)	(728,000)
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate				5.20%	5.80%	6.20%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.50%			4.50%	5.20%	5.80%
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	10,027,000			10,027,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	10,280,000			10,280,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	10,533,000			10,533,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	10,721,000			10,721,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	10,856,000			10,856,000
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	54,752,000			54,752,000
Coal Workers Pneumoconiosis [Member] | PPACA Legislation [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic (benefit) cost					6,658
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Amounts Recognized in Balance Sheet					45,700
Coal Workers Pneumoconiosis [Member] | remeasurent and assumption changes [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic (benefit) cost					10,576
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Amounts Recognized in Balance Sheet					47,700
Coal Workers Pneumoconiosis [Member] | All Other [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic (benefit) cost					3,918
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Amounts Recognized in Balance Sheet					1,232
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Deferred Income Tax Expense (Benefit)					768
Workers Compensation [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost				17,872,000	27,015,000	28,394,000
Interest cost				8,238,000	9,156,000	8,765,000
Post Employment Benefit Plan Legal And Administrative Costs				2,143,000	3,384,000	3,401,000
Amortization of actuarial gain				3,907,000	3,072,000	4,200,000
State administrative fees and insurance bond premiums				7,035,000	7,816,000	6,710,000
Legal and administrative costs				20,015,000	30,399,000
Net periodic (benefit) cost	31,381,000	44,299,000		43,070,000
Legal and administrative costs				20,015,000	30,399,000
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	174,069,000			174,069,000	174,456,000	179,268,000
Defined Benefit Plan, Actuarial Net (Gains) Losses				(2,783,000)	(14,553,000)
Defined Benefit Plan, Benefits Paid				(32,892,000)	(37,630,000)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	149,232,000			149,232,000	(146,702,000)
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(174,069,000)			(174,069,000)	(174,456,000)
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	(24,837,000)			(24,837,000)	(27,754,000)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(55,233,000)			(55,233,000)	(56,358,000)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax	0			0	0
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(55,233,000)			(55,233,000)	(56,358,000)
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Defined Benefit Plan, Amortization of Net Gains (Losses)			(3,944,000)
Defined Benefit Plan, Amortization of Net Prior Service Cost (Credit)			0	0	0	0
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate				5.10%	5.60%	5.90%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.40%			4.40%	5.10%	5.60%
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	31,375,000			31,375,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	31,360,000			31,360,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	31,576,000			31,576,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	31,925,000			31,925,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	32,328,000			32,328,000
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	169,785,000			169,785,000
Workers Compensation [Member] | Actuarial Benefits [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	24,837,000			24,837,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	24,658,000			24,658,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	24,707,000			24,707,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	24,884,000			24,884,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	25,111,000			25,111,000
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	130,900,000			130,900,000
Workers Compensation [Member] | Other Workers Comp benefits [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	6,538,000			6,538,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	6,702,000			6,702,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	6,869,000			6,869,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	7,041,000			7,041,000
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	7,217,000			7,217,000
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 38,885,000			$ 38,885,000