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Revenue derived from sale of coal and related products. Also includes rendering of services and selling of products for exploration, development, mining, and processing, as well as supporting activities.

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount after accretion (amortization) of discount (premium), and investment expense, of interest income and dividend income on nonoperating securities.

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Accumulated Other Comprehensive Income (Loss) (Schedule of Reclassifications) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 745,192us-gaap_CoalProductsAndServicesRevenue	$ 742,180us-gaap_CoalProductsAndServicesRevenue	$ 713,776us-gaap_CoalProductsAndServicesRevenue	$ 735,971us-gaap_CoalProductsAndServicesRevenue	$ 719,386us-gaap_CoalProductsAndServicesRevenue	$ 791,269us-gaap_CoalProductsAndServicesRevenue	$ 766,332us-gaap_CoalProductsAndServicesRevenue	$ 737,370us-gaap_CoalProductsAndServicesRevenue	$ 2,937,119us-gaap_CoalProductsAndServicesRevenue	$ 3,014,357us-gaap_CoalProductsAndServicesRevenue	$ 3,768,126us-gaap_CoalProductsAndServicesRevenue
Loss from continuing operations before income taxes									(532,719)	(1,080,726)	(1,092,822)
Provision for (benefit from) income taxes									(25,634)us-gaap_IncomeTaxExpenseBenefit	335,498us-gaap_IncomeTaxExpenseBenefit	353,907us-gaap_IncomeTaxExpenseBenefit
Net income (loss)	(240,135)us-gaap_ProfitLoss	(97,218)us-gaap_ProfitLoss	(96,860)us-gaap_ProfitLoss	(124,140)us-gaap_ProfitLoss	(371,214)us-gaap_ProfitLoss	(128,363)us-gaap_ProfitLoss	(72,206)us-gaap_ProfitLoss	(70,049)us-gaap_ProfitLoss	(558,353)us-gaap_ProfitLoss	(641,832)us-gaap_ProfitLoss	(683,687)us-gaap_ProfitLoss
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									9,885	386
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									1,692	1,847
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									5,736	(916)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									2,457	(545)
Reclassification out of accumulated other comprehensive income [Member] \| Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Commodity Contract [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues									2,643	2,886
Provision for (benefit from) income taxes									(951)	(1,039)
Net income (loss)									1,692	1,847
Reclassification out of accumulated other comprehensive income [Member] \| Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service credits									11,760	13,705
Amortization of net actuarial gains (losses)									(2,797)	(15,136)
Loss from continuing operations before income taxes									8,963	(1,431)
Provision for (benefit from) income taxes									(3,227)	515
Net income (loss)									5,736	(916)
Reclassification out of accumulated other comprehensive income [Member] \| Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and investment income									3,838	(852)
Provision for (benefit from) income taxes									(1,381)	307
Net income (loss)									$ 2,457	$ (545)