Income Taxes Deferred Asset and Liability Sched (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Other	$ 136,211	$ 129,293
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	54,998	141,758
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions	103,146	65,309
Deferred Tax Assets, Operating Loss Carryforwards	57,669	58,428
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Deferred Rent	24,763	27,918
Deferred Tax Assets, Gross	1,889,598	2,023,000
Deferred Tax Assets, Valuation Allowance	(41,016)	(62,668)
Deferred Tax Assets	1,848,582	1,960,332
Components of Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment	(1,046,235)	(1,221,362)
Deferred Tax Liabilities, Derivatives	(98,539)	(29,209)
Deferred Tax Liabilities, Deferred Expense, Other Capitalized Costs	(31,284)	(31,574)
Deferred Tax Liabilities, Other	(23,717)	(19,170)
Deferred Tax Liabilities	(1,199,775)	(1,301,315)
Deferred Tax Assets, Valuation Allowance, Noncurrent	(41,016)	(61,890)
Deferred Tax Assets, Valuation Allowance, Current		(778)
Deferred Tax Assets (Liabilities), Net	648,807	659,017
Income Tax Reconciliation, Prior Year Income Taxes	2,257	4,609	(1,256)
State Operating Losses [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Valuation Allowance	34,980	39,744
Other Tax Carryforward, Name [Domain]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Valuation Allowance	6,036	22,924
Other Comprehensive Income (Loss) [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Valuation Allowance	872	9,639
Other Postretirement Benefit Plans, Defined Benefit [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits	1,217,246	1,251,641
Workers Compensation [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits	65,266	67,025
Subsidence [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Other	41,453	34,659
Coal Workers Pneumoconiosis [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits	69,915	71,661
reclamation [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Asset Retirement Obligations	23,738	31,177
Mine Closing [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Asset Retirement Obligations	95,193	144,131
alternative minimum [Member]
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	55,251
Components of Deferred Tax Liabilities [Abstract]
Income Tax Reconciliation, Prior Year Income Taxes	25,687
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	$ 5,823