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Fair Value of Derivative and Other Financial Instruments - Derivative Balance Sheet Information (Details) (USD $) | Mar. 31, 2015 | Dec. 31, 2014
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Derivatives, Fair Value [Line Items] |  |
Current assets | $ 9,342,000 us-gaap_DerivativeAssetsCurrent | $ 11,232,000 us-gaap_DerivativeAssetsCurrent
Commodity derivative instruments, Current liabilities | (1,235,000)us-gaap_DerivativeLiabilitiesCurrent | (1,209,000)us-gaap_DerivativeLiabilitiesCurrent
Commodity derivative instruments, Long-term liabilities | (277,000)us-gaap_DerivativeLiabilitiesNoncurrent | (477,000)us-gaap_DerivativeLiabilitiesNoncurrent
Assets, Current | 503,721,000 us-gaap_AssetsCurrent | 432,817,000 us-gaap_AssetsCurrent
PNMR and PNM [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, Collateral, Right to Reclaim Cash | 0 us-gaap_DerivativeCollateralRightToReclaimCash / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 0 us-gaap_DerivativeCollateralRightToReclaimCash / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Margin Deposit Assets | 2,800,000 us-gaap_MarginDepositAssets / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 3,800,000 us-gaap_MarginDepositAssets / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Derivative, Collateral, Obligation to Return Cash | 200,000 us-gaap_DerivativeCollateralObligationToReturnCash / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 200,000 us-gaap_DerivativeCollateralObligationToReturnCash / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Fair Value Hedging [Member] | Commodity Contract [Member] | PNMR and PNM [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Current assets | 9,342,000 us-gaap_DerivativeAssetsCurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 11,232,000 us-gaap_DerivativeAssetsCurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Deferred charges | 0 us-gaap_DerivativeAssetsNoncurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 0 us-gaap_DerivativeAssetsNoncurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Assets | 9,342,000 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 11,232,000 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Current liabilities | (1,235,000)us-gaap_DerivativeLiabilitiesCurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | (1,209,000)us-gaap_DerivativeLiabilitiesCurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Long-term liabilities | (277,000)us-gaap_DerivativeLiabilitiesNoncurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | (477,000)us-gaap_DerivativeLiabilitiesNoncurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Liabilities | (1,512,000)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | (1,686,000)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Commodity derivative instruments, Net | 7,830,000 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | 9,546,000 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember
Fuel and Purchased Power Adjustment Clause [Member] | Fair Value Hedging [Member] | Commodity Contract [Member] | Public Service Company of New Mexico [Member] | Maximum [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Assets, Current | 100,000 us-gaap_AssetsCurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_RangeAxis = us-gaap_MaximumMember / pnm_ScheduleOfRegulatoryRateMattersAxis = pnm_FuelAndPurchasedPowerAdjustmentClauseMember |
Palo Verde Nuclear Generating Station [Member] | Fair Value Hedging [Member] | Commodity Contract [Member] | PNMR and PNM [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Current assets | $ 2,200,000 us-gaap_DerivativeAssetsCurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember | $ 3,000,000 us-gaap_DerivativeAssetsCurrent / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember

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