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Variable Interest Entities (Details) (USD $) | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014 | Oct. 08, 2013
Variable Interest Entity, Statement Of Operation [Abstract] |  |  |  |
Earnings attributable to non-controlling interest | $ 3,380,000 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | $ 3,531,000 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |
Current assets | 503,721,000 us-gaap_AssetsCurrent |  | 432,817,000 us-gaap_AssetsCurrent |
Total assets | 5,939,339,000 us-gaap_Assets | 5,507,026,000 us-gaap_Assets | 5,829,325,000 us-gaap_Assets |
Current liabilities | 693,034,000 us-gaap_LiabilitiesCurrent |  | 704,282,000 us-gaap_LiabilitiesCurrent |
Owners’ equity – non-controlling interest | 72,766,000 us-gaap_MinorityInterest |  | 73,546,000 us-gaap_MinorityInterest |
Net earnings | 14,340,000 us-gaap_NetIncomeLoss | 12,468,000 us-gaap_NetIncomeLoss |  |
Public Service Company of New Mexico [Member] |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |
Operating Leases, Renewal Options After Original Lease Term (in years) | 2 years |  |  |
Operating Leases, Extended Lease Term Option (in years) | 6 years |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |
Operating Leases, Future Minimum Payments Due, Next Six Months | 8,400,000 pnm_OperatingLeasesFutureMinimumPaymentsDueNextSixMonths / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |  | 26,000,000 pnm_OperatingLeasesFutureMinimumPaymentsDueNextSixMonths / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Property Lease Guarantee [Member] | Maximum [Member] |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |
Loss Contingency, Range of Possible Loss, Portion Not Accrued | 217,300,000.0 us-gaap_LossContingencyRangeOfPossibleLossPortionNotAccrued / us-gaap_JointlyOwnedUtilityPlantAxis = pnm_PaloVerdeNuclearGeneratingStationMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LossContingenciesByNatureOfContingencyAxis = us-gaap_PropertyLeaseGuaranteeMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |
Valencia [Member] | Public Service Company of New Mexico [Member] |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Long Term Contract For Purchase of Electric Power Fixed Costs | 4,800,000 pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 4,800,000 pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |
Long Term Contract For Purchase of Electric Power Variable Charges | 100,000 pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 200,000 pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |
Variable Interest Entity, Statement Of Operation [Abstract] |  |  |  |
Operating revenues | 4,904,000 pnm_ResultsOfOperationsVariableInterestEntityOperatingRevenues / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 4,931,000 pnm_ResultsOfOperationsVariableInterestEntityOperatingRevenues / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |
Operating expenses | (1,524,000)pnm_ResultsOfOperationsVariableInterestEntityOperatingExpenses / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | (1,400,000)pnm_ResultsOfOperationsVariableInterestEntityOperatingExpenses / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |
Earnings attributable to non-controlling interest | 3,380,000 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 3,531,000 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |
Current assets | 2,839,000 us-gaap_AssetsCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 2,513,000 us-gaap_AssetsCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Net property, plant, and equipment | 71,679,000 us-gaap_PropertyPlantAndEquipmentNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 72,321,000 us-gaap_PropertyPlantAndEquipmentNet / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Total assets | 74,518,000 us-gaap_Assets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 74,834,000 us-gaap_Assets / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Current liabilities | 1,752,000 us-gaap_LiabilitiesCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 1,288,000 us-gaap_LiabilitiesCurrent / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Owners’ equity – non-controlling interest | 72,766,000 us-gaap_MinorityInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  | 73,546,000 us-gaap_MinorityInterest / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |
Long term contract option to purchase, ownership percentage | 50.00%pnm_Longtermcontractoptiontopurchaseownershippercentage / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |
Long term contract option to purchase, purchase price - percentage of adjusted NBV | 50.00%pnm_LongtermcontractoptiontopurchasepurchasepricepercentageofadjustedNBV / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |
Long term contract option to purchase, purchase price - percentage of FMV | 50.00%pnm_LongtermcontractoptiontopurchasepurchasepricepercentageofFMV / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |
Long term contract option to purchase, number of days to set FMV | 60 days |  |  |
Long term contract option to purchase, estimated purchase price |  |  |  | 85,000,000 pnm_Longtermcontractoptiontopurchaseestimatedpurchaseprice / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Long term contract option to purchase, approximate approval period | 15 months |  |  |
Valencia [Member] | Public Service Company of New Mexico [Member] | Purchased Through May 30, 2028 [Member] |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Number of mega watts purchased (in megawatts) | 158 pnm_NumberOfMegaWattsPurchased / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_LongTermContractForPurchaseOfElectricPowerAxis = pnm_PurchasedThroughMay302028Member / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |
Variable Interest Entity, Not Primary Beneficiary [Member] | Public Service Company of New Mexico [Member] |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |
Operating leases, future minimum payments due, renewal term | 150,500,000 pnm_Operatingleasesfutureminimumpaymentsduerenewalterm / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember |  |  |
Delta [Member] | Public Service Company of New Mexico [Member] |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Long Term Contract For Purchase of Electric Power Fixed Costs |  | 1,600,000 pnm_LongTermContractForPurchaseOfElectricPowerFixedCosts / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = pnm_DeltaMember |  |
Long Term Contract For Purchase of Electric Power Variable Charges |  | 200,000 pnm_LongTermContractForPurchaseOfElectricPowerVariableCharges / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = pnm_DeltaMember |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |
Period of Long Term Contract For Purchase of Electric Power Fixed Costs | 20 years |  |  |
Delta [Member] | Public Service Company of New Mexico [Member] | Delta [Member] |  |  |  |
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract] |  |  |  |
Revenues |  | 1,800,000 us-gaap_Revenues / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = pnm_DeltaMember |  |
Net earnings |  | $ 300,000 us-gaap_NetIncomeLoss / us-gaap_BusinessAcquisitionAxis = pnm_DeltaMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = pnm_DeltaMember |  |

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