1.0.0.3 false Condensed Consolidated Balance Sheets (USD $) In Thousands false 1 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u001 Standard http://www.xbrl.org/2003/instance shares xbrli 0 false 2 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u001 Standard http://www.xbrl.org/2003/instance shares xbrli 0 6 Current assets 4 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 7 Cash and cash equivalents 5 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 true true 481557000 481557 false false 2 true true 676190000 676190 false false No definition available. No authoritative reference available. false 8 Trade accounts receivable, net 5 us-gaap_AccountsReceivableNetCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 265848000 265848 false false 2 false true 163674000 163674 false false No definition available. No authoritative reference available. false 9 Deferred income taxes 5 us-gaap_DeferredTaxAssetsNetCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 26101000 26101 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 10 Inventories, net 5 us-gaap_InventoryNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 187855000 187855 false false 2 false true 86594000 86594 false false No definition available. No authoritative reference available. false 11 Prepaid expenses and other current assets 5 us-gaap_PrepaidExpenseCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 105887000 105887 false false 2 false true 65325000 65325 false false No definition available. No authoritative reference available. false 12 Total current assets 5 us-gaap_AssetsCurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1067248000 1067248 false false 2 false true 991783000 991783 false false No definition available. No authoritative reference available. true 13 Property, equipment and mine development costs, net 4 us-gaap_PropertyPlantAndEquipmentNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1063216000 1063216 false false 2 false true 356758000 356758 false false No definition available. No authoritative reference available. false 14 Owned and leased mineral rights, net 4 us-gaap_MineralRights us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 2027573000 2027573 false false 2 false true 180458000 180458 false false No definition available. No authoritative reference available. false 15 Owned lands 4 us-gaap_Land us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 89588000 89588 false false 2 false true 12882000 12882 false false No definition available. No authoritative reference available. false 16 Goodwill 4 us-gaap_Goodwill us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 372551000 372551 false false 2 false true 20547000 20547 false false No definition available. No authoritative reference available. false 17 Acquired coal supply agreements, net 4 anr_AcquiredCoalSupplyAgreementsNet anr false na instant monetary Net carrying amount as of the balance sheet date of an intangible asset that arises from a contractual arrangement with a... false false false false false false false false false 1 false true 434807000 434807 false false 2 false true 2090000 2090 false false Net carrying amount as of the balance sheet date of an intangible asset that arises from a contractual arrangement with a third party (not including franchise rights and license agreements). No authoritative reference available. false 18 Deferred income taxes 4 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 19 Other non-current assets 4 us-gaap_OtherAssetsNoncurrent us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 66814000 66814 false false 2 false true 61631000 61631 false false No definition available. No authoritative reference available. false 20 Total assets 4 us-gaap_Assets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 5121797000 5121797 false false 2 false true 1709838000 1709838 false false No definition available. No authoritative reference available. true 22 Current liabilities 4 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 23 Current portion of long-term debt 5 us-gaap_LongTermDebtCurrent 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 24 Note payable 5 us-gaap_NotesPayableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1859000 1859 false false 2 false true 18288000 18288 false false No definition available. No authoritative reference available. false 25 Trade accounts payable 5 us-gaap_AccountsPayableCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 146054000 146054 false false 2 false true 102975000 102975 false false No definition available. No authoritative reference available. false 26 Accrued expenses and other current liabilities 5 us-gaap_AccruedLiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 250653000 250653 false false 2 false true 140459000 140459 false false No definition available. No authoritative reference available. false 27 Total current liabilities 5 us-gaap_LiabilitiesCurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 432066000 432066 false false 2 false true 261954000 261954 false false No definition available. No authoritative reference available. true 28 Long-term debt 4 us-gaap_LongTermDebtAndCapitalLeaseObligations us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 756553000 756553 false false 2 false true 432795000 432795 false false No definition available. No authoritative reference available. false 29 Pension and postretirement medical benefit obligations 4 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 698557000 698557 false false 2 false true 60211000 60211 false false No definition available. No authoritative reference available. false 30 Asset retirement obligations 4 us-gaap_AssetRetirementObligationsNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 195595000 195595 false false 2 false true 90565000 90565 false false No definition available. No authoritative reference available. false 31 Deferred income taxes 4 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 340174000 340174 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 32 Other non-current liabilities 4 us-gaap_OtherLiabilitiesNoncurrent us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 151982000 151982 false false 2 false true 68621000 68621 false false No definition available. No authoritative reference available. false 33 Total liabilities 4 us-gaap_Liabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2574927000 2574927 false false 2 false true 914146000 914146 false false No definition available. No authoritative reference available. true 35 Stockholders' equity 4 us-gaap_StockholdersEquityAbstract 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 36 Preferred stock - par value $0.01, 10,000,000 shares authorized, none issued 5 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 37 Common stock - par value $0.01, 200,000,000 shares authorized, 120,530,503 issued and 120,229,288 outstanding at September 30, 2009 and 70,513,8800 issued and oustanding at December 31, 2008 5 us-gaap_CommonStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1205000 1205 false false 2 false true 705000 705 false false No definition available. No authoritative reference available. false 38 Additional paid-in capital 5 us-gaap_AdditionalPaidInCapital us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2180153000 2180153 false false 2 false true 484261000 484261 false false No definition available. No authoritative reference available. false 39 Accumulated other comprehensive loss 5 us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true -3650000 -3650 false false 2 false true -30107000 -30107 false false No definition available. No authoritative reference available. false 40 Treasury stock, at cost: 301,215 and 0 shares at September 30, 2009 and December 31, 2008, respectively 5 us-gaap_TreasuryStockValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true -8495000 -8495 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 41 Retained earnings 5 us-gaap_RetainedEarningsAccumulatedDeficit us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 377657000 377657 false false 2 false true 340833000 340833 false false No definition available. No authoritative reference available. false 42 Total stockholders' equity 5 us-gaap_StockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2546870000 2546870 false false 2 false true 795692000 795692 false false No definition available. No authoritative reference available. true 43 Total liabilities and stockholders' equity 4 us-gaap_LiabilitiesAndStockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 true true 5121797000 5121797 false false 2 true true 1709838000 1709838 false false No definition available. No authoritative reference available. true false 2 36 false Thousands UnKnown UnKnown false true