1.0.0.3 true Statements of Shareholders Equity and Comprehensive Income (Parenthetical) (USD $) false 1 $ true false false false Total Alpha Natural Resources Inc. Equity us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_ParentMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 2 $ true false false false Common Stock us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis explicitMember Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 3 $ true false false false Additional Paid-in Capital us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AdditionalPaidInCapitalMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 4 $ true false false false Accumulated Other Comprehensive Income (Loss) us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AccumulatedOtherComprehensiveIncomeMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 5 $ false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 5 Comprehensive income 3 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 false false 3 false false 0 0 false false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. false 6 Tax effect on unrealized gains (losses) 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 true true 2070000 2070000 true false 2 false false 0 0 false false 3 false false 0 0 false false 4 true true 2070000 2070000 true false 5 true true 2070000 2070000 false false No definition available. No authoritative reference available. false 8 Tax effect on adjustments to unrecognized gains and losses and amortization of employee benefit costs 4 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansTax us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false true -997000 -997000 true false 2 false false 0 0 false false 3 false false 0 0 false false 4 false true -997000 -997000 true false 5 false true 997000 997000 false false No definition available. No authoritative reference available. false 5 Comprehensive income 3 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. false 6 Tax effect on unrealized gains (losses) 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 3111000 3111000 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true 3111000 3111000 true false 5 false true 3111000 3111000 false false No definition available. 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No authoritative reference available. false 11 Offering costs of public offering of common shares 3 anr_OfferingCostsOfPublicOfferingOfCommonShares anr false debit duration monetary Offering costs of public offering of common shares. false false false false false false false false false 1 false true 7834000 7834000 true false 2 false true 7834000 7834000 true false 3 false true 7834000 7834000 true false 4 false false 0 0 true false 5 false true 7834000 7834000 false false Offering costs of public offering of common shares. No authoritative reference available. false 12 Proceeds from public offering of common shares, per share 3 anr_ProceedsFromPublicOfferingOfCommonSharesPerShare anr false na duration monetary Proceeds from public offering of common shares, per share. false false false false false false false false false 1 false false 0 0 true false 2 false true 41.25 41.25 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false Proceeds from public offering of common shares, per share. No authoritative reference available. false 5 Comprehensive income 3 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 false false 3 false false 0 0 false false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. false 6 Tax effect on unrealized gains (losses) 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -552000 -552000 true false 2 false false 0 0 false false 3 false false 0 0 false false 4 false true -552000 -552000 true false 5 false true 552000 552000 false false No definition available. No authoritative reference available. false 7 Tax effect on change in fair value of available-for-sale marketable securities 4 us-gaap_OtherComprehensiveIncomeAvailableForSaleSecuritiesTax us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false true 140000 140000 true false 2 false false 0 0 false false 3 false false 0 0 false false 4 false true 140000 140000 true false 5 false true 140000 140000 false false No definition available. No authoritative reference available. false 8 Tax effect on adjustments to unrecognized gains and losses and amortization of employee benefit costs 4 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansTax us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false true -9092000 -9092000 true false 2 false false 0 0 false false 3 false false 0 0 false false 4 false true -9092000 -9092000 true false 5 false true 9092000 9092000 false false No definition available. No authoritative reference available. false 9 Tax effect on amounts reclassified to earnings related to the termination of hedge accounting 4 us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentOnDerivativesIncludedInNetIncomeTax us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true -6968000 -6968000 true false 2 false false 0 0 false false 3 false false 0 0 false false 4 true true -6968000 -6968000 true false 5 true true 6968000 6968000 false false No definition available. No authoritative reference available. false false 5 14 false NoRounding UnKnown UnKnown false true