1.0.0.3 false Consolidated Balance Sheets (USD $) In Thousands false 1 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 2 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 4 Current assets: 2 us-gaap_AssetsCurrentAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 5 Cash and cash equivalents 3 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 true true 465869000 465869 false false 2 true true 676190000 676190 false false No definition available. No authoritative reference available. false 6 Trade accounts receivable, net 3 us-gaap_AccountsReceivableNetCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 232631000 232631 false false 2 false true 163674000 163674 false false No definition available. No authoritative reference available. false 7 Inventories, net 3 us-gaap_InventoryNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 176372000 176372 false false 2 false true 86594000 86594 false false No definition available. No authoritative reference available. false 8 Prepaid expenses and other current assets 3 anr_PrepaidExpensesAndOtherCurrentAssets anr false debit instant monetary Prepaid expenses and other current assets. false false false false false false false false false 1 false true 176953000 176953 false false 2 false true 65325000 65325 false false Prepaid expenses and other current assets. No authoritative reference available. true 9 Total current assets 3 us-gaap_AssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1051825000 1051825 false false 2 false true 991783000 991783 false false No definition available. No authoritative reference available. false 10 Property, equipment and mine development costs, net 2 us-gaap_PropertyPlantAndEquipmentNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1082446000 1082446 false false 2 false true 356758000 356758 false false No definition available. No authoritative reference available. false 11 Owned and leased mineral rights, net 2 us-gaap_MineralRights us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1985855000 1985855 false false 2 false true 180458000 180458 false false No definition available. No authoritative reference available. false 12 Owned lands 2 us-gaap_Land us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 91262000 91262 false false 2 false true 12882000 12882 false false No definition available. No authoritative reference available. false 13 Goodwill 2 us-gaap_Goodwill us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 357868000 357868 false false 2 false true 20547000 20547 false false No definition available. No authoritative reference available. false 14 Acquired coal supply agreements, net 2 us-gaap_FiniteLivedIntangibleAssetsNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 396491000 396491 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 15 Deferred income taxes 2 us-gaap_DeferredTaxAssetsNetNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true 83689000 83689 false false No definition available. No authoritative reference available. false 16 Other non-current assets 2 us-gaap_OtherAssetsNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 157024000 157024 false false 2 false true 63721000 63721 false false No definition available. No authoritative reference available. true 17 Total assets 2 us-gaap_Assets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 5122771000 5122771 false false 2 false true 1709838000 1709838 false false No definition available. No authoritative reference available. true 19 Current liabilities: 2 us-gaap_LiabilitiesCurrentAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 20 Current portion of long-term debt 3 us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 33500000 33500 false false 2 false true 232000 232 false false No definition available. No authoritative reference available. false 21 Note payable 3 us-gaap_NotesPayableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true 18288000 18288 false false No definition available. No authoritative reference available. false 22 Trade accounts payable 3 us-gaap_AccountsPayableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 143400000 143400 false false 2 false true 102975000 102975 false false No definition available. No authoritative reference available. false 23 Accrued expenses and other current liabilities 3 us-gaap_AccruedLiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 258293000 258293 false false 2 false true 140459000 140459 false false No definition available. No authoritative reference available. true 24 Total current liabilities 3 us-gaap_LiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 435193000 435193 false false 2 false true 261954000 261954 false false No definition available. No authoritative reference available. false 25 Long-term debt 2 us-gaap_LongTermDebtAndCapitalLeaseObligations us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 756753000 756753 false false 2 false true 432795000 432795 false false No definition available. No authoritative reference available. false 26 Pension and postretirement medical benefit obligations 2 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 682991000 682991 false false 2 false true 60211000 60211 false false No definition available. No authoritative reference available. false 27 Asset retirement obligations 2 us-gaap_AssetRetirementObligationsNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 190724000 190724 false false 2 false true 90565000 90565 false false No definition available. No authoritative reference available. false 28 Deferred income taxes 2 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 316464000 316464 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 29 Other non-current liabilities 2 us-gaap_OtherLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 149357000 149357 false false 2 false true 68621000 68621 false false No definition available. No authoritative reference available. true 30 Total liabilities 2 us-gaap_Liabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2531482000 2531482 false false 2 false true 914146000 914146 false false No definition available. No authoritative reference available. true 32 Stockholders' equity: 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 33 Preferred stock - par value $0.01, 10,000,000 shares authorized, none issued 3 us-gaap_PreferredStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 34 Common stock - par value $0.01, 200,000,000 shares authorized,120,782,952 issued and 120,473,495 outstanding at December 31, 2009 and 70,513,880 issued and outstanding at December 31, 2008 3 us-gaap_CommonStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1208000 1208 false false 2 false true 705000 705 false false No definition available. No authoritative reference available. false 35 Additional paid-in capital 3 us-gaap_AdditionalPaidInCapitalCommonStock us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2194305000 2194305 false false 2 false true 484261000 484261 false false No definition available. No authoritative reference available. false 36 Accumulated other comprehensive income (loss) 3 us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 5812000 5812 false false 2 false true -30107000 -30107 false false No definition available. No authoritative reference available. false 37 Treasury stock, at cost: 309,457 and 0 shares at December 31, 2009 and December 31, 2008, respectively 3 us-gaap_TreasuryStockValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true -8874000 -8874 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 38 Retained earnings 3 us-gaap_RetainedEarningsAccumulatedDeficit us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 398838000 398838 false false 2 false true 340833000 340833 false false No definition available. No authoritative reference available. true 39 Total stockholders' equity 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2591289000 2591289 false false 2 false true 795692000 795692 false false No definition available. No authoritative reference available. true 40 Total liabilities and stockholders' equity 2 us-gaap_LiabilitiesAndStockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 true true 5122771000 5122771 false false 2 true true 1709838000 1709838 false false No definition available. No authoritative reference available. true false 2 35 false Thousands UnKnown UnKnown false true