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Regulatory Matters (Schedule Of Asset And Liability) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Regulated Asset Liability [Line Items]    
Earning a return, asset $ 191,490ava_RegulatoryAssetEarningReturn  
Not earning a return, asset 383,014us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided  
Pending regulatory treatment, asset 4,496us-gaap_AmountOfRegulatoryCostsNotYetApproved  
Total, asset 579,000us-gaap_RegulatoryAssets 384,355us-gaap_RegulatoryAssets
Earning a return, liability 278,166ava_RegulatoryLiabilityEarningReturn  
Not earning a return, liability 20,578ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided  
Pending Regulatory Treatment Liability 34,884ava_PendingRegulatoryTreatmentLiability  
Total, liability 333,628us-gaap_RegulatoryLiabilities 354,281us-gaap_RegulatoryLiabilities
Natural Gas Deferrals [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 3,921ava_RegulatoryLiabilityEarningReturn
/ us-gaap_RegulatoryLiabilityAxis
= ava_NaturalGasDeferralsMember		  
Not earning a return, liability 0ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryLiabilityAxis
= ava_NaturalGasDeferralsMember		  
Pending Regulatory Treatment Liability 0ava_PendingRegulatoryTreatmentLiability
/ us-gaap_RegulatoryLiabilityAxis
= ava_NaturalGasDeferralsMember		  
Total, liability 3,921us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_NaturalGasDeferralsMember		 12,075us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_NaturalGasDeferralsMember
Power Deferrals [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 14,186ava_RegulatoryLiabilityEarningReturn
/ us-gaap_RegulatoryLiabilityAxis
= ava_PowerDeferralsRegulatoryLiabilityMember		  
Not earning a return, liability 0ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryLiabilityAxis
= ava_PowerDeferralsRegulatoryLiabilityMember		  
Pending Regulatory Treatment Liability 0ava_PendingRegulatoryTreatmentLiability
/ us-gaap_RegulatoryLiabilityAxis
= ava_PowerDeferralsRegulatoryLiabilityMember		  
Total, liability 14,186us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_PowerDeferralsRegulatoryLiabilityMember		 17,904us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_PowerDeferralsRegulatoryLiabilityMember
Removal Costs [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 254,140ava_RegulatoryLiabilityEarningReturn
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_RemovalCostsMember		  
Not earning a return, liability 0ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_RemovalCostsMember		  
Pending Regulatory Treatment Liability 0ava_PendingRegulatoryTreatmentLiability
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_RemovalCostsMember		  
Total, liability 254,140us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_RemovalCostsMember		 242,850us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_RemovalCostsMember
Income Tax Related Liabilities [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 0ava_RegulatoryLiabilityEarningReturn
/ us-gaap_RegulatoryLiabilityAxis
= ava_IncomeTaxRelatedLiabilitiesMember		  
Not earning a return, liability 14,534ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryLiabilityAxis
= ava_IncomeTaxRelatedLiabilitiesMember		  
Pending Regulatory Treatment Liability 0ava_PendingRegulatoryTreatmentLiability
/ us-gaap_RegulatoryLiabilityAxis
= ava_IncomeTaxRelatedLiabilitiesMember		  
Total, liability 14,534us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_IncomeTaxRelatedLiabilitiesMember		 9,203us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_IncomeTaxRelatedLiabilitiesMember
Regulatory Liability for Interest Rate Swaps [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 0ava_RegulatoryLiabilityEarningReturn
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForInterestRateSwapsMember		  
Not earning a return, liability 460ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForInterestRateSwapsMember		  
Pending Regulatory Treatment Liability 0ava_PendingRegulatoryTreatmentLiability
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForInterestRateSwapsMember		  
Total, liability 460us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForInterestRateSwapsMember		 33,543us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForInterestRateSwapsMember
Regulatory Liability For Production Facility [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 0ava_RegulatoryLiabilityEarningReturn
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForProductionFacilityMember		  
Not earning a return, liability 0ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForProductionFacilityMember		  
Pending Regulatory Treatment Liability 29,028ava_PendingRegulatoryTreatmentLiability
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForProductionFacilityMember		  
Total, liability 29,028us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForProductionFacilityMember		 25,046us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_RegulatoryLiabilityForProductionFacilityMember
Other Regulatory Assets [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 5,919ava_RegulatoryLiabilityEarningReturn
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember		  
Not earning a return, liability 1,309ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember		  
Pending Regulatory Treatment Liability 0ava_PendingRegulatoryTreatmentLiability
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember		  
Total, liability 7,228us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember		 11,170us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Revenue Subject to Refund Cumulative [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, liability 0ava_RegulatoryLiabilityEarningReturn
/ us-gaap_RegulatoryLiabilityAxis
= ava_RevenueSubjecttoRefundCumulativeMember		  
Not earning a return, liability 4,275ava_RemainingAmountsOfRegulatoryLiabilitiesForWhichNoInterestDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryLiabilityAxis
= ava_RevenueSubjecttoRefundCumulativeMember		  
Pending Regulatory Treatment Liability 5,856ava_PendingRegulatoryTreatmentLiability
/ us-gaap_RegulatoryLiabilityAxis
= ava_RevenueSubjecttoRefundCumulativeMember		  
Total, liability 10,131us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_RevenueSubjecttoRefundCumulativeMember		 2,490us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ava_RevenueSubjecttoRefundCumulativeMember
Investment In Exchange Power-Net [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory assets 2019  
Earning a return, asset 11,433ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_InvestmentInExchangePowerNetMember		  
Not earning a return, asset 0us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_InvestmentInExchangePowerNetMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_InvestmentInExchangePowerNetMember		  
Total, asset 11,433us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_InvestmentInExchangePowerNetMember		 13,883us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_InvestmentInExchangePowerNetMember
Deferred Income Tax Charge [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 100,412ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= us-gaap_DeferredIncomeTaxChargesMember		  
Not earning a return, asset 0us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= us-gaap_DeferredIncomeTaxChargesMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= us-gaap_DeferredIncomeTaxChargesMember		  
Total, asset 100,412us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_DeferredIncomeTaxChargesMember		 71,421us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_DeferredIncomeTaxChargesMember
Pension and Other Postretirement Plans Costs [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionAndOtherPostretirementPlansCostsMember		  
Not earning a return, asset 235,758us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionAndOtherPostretirementPlansCostsMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionAndOtherPostretirementPlansCostsMember		  
Total, asset 235,758us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionAndOtherPostretirementPlansCostsMember		 156,984us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionAndOtherPostretirementPlansCostsMember
Current Regulatory Asset For Utility Derivatives [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_CurrentRegulatoryAssetForUtilityDerivativesMember		  
Not earning a return, asset 29,640us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_CurrentRegulatoryAssetForUtilityDerivativesMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_CurrentRegulatoryAssetForUtilityDerivativesMember		  
Total, asset 29,640us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_CurrentRegulatoryAssetForUtilityDerivativesMember		 10,829us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_CurrentRegulatoryAssetForUtilityDerivativesMember
Unamortized Debt Repurchase Costs [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 17,357ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_UnamortizedDebtRepurchaseCostsMember		  
Not earning a return, asset 0us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_UnamortizedDebtRepurchaseCostsMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_UnamortizedDebtRepurchaseCostsMember		  
Total, asset 17,357us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_UnamortizedDebtRepurchaseCostsMember		 19,417us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_UnamortizedDebtRepurchaseCostsMember
Regulatory Asset For Settlement With Coeur d'Alene Tribe [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory assets 2059  
Earning a return, asset 47,887ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetSettlementMember		  
Not earning a return, asset 0us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetSettlementMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetSettlementMember		  
Total, asset 47,887us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetSettlementMember		 49,198us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetSettlementMember
Demand Side Management Programs [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_DemandSideManagementProgramsMember		  
Not earning a return, asset 4,603us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_DemandSideManagementProgramsMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_DemandSideManagementProgramsMember		  
Total, asset 4,603us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_DemandSideManagementProgramsMember		 9,576us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_DemandSideManagementProgramsMember
Montana Lease Payments [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 1,984ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_LeasePaymentsMember		  
Not earning a return, asset 0us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_LeasePaymentsMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_LeasePaymentsMember		  
Total, asset 1,984us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_LeasePaymentsMember		 3,022us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_LeasePaymentsMember
Lancaster Plant 2010 Net Costs [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory assets 2015  
Earning a return, asset 1,247ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_PlantNetCostsMember		  
Not earning a return, asset 0us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_PlantNetCostsMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_PlantNetCostsMember		  
Total, asset 1,247us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_PlantNetCostsMember		 2,607us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_PlantNetCostsMember
Deferred Maintenance Costs [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory assets 2017  
Earning a return, asset 0ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_DeferredMaintenanceCostsMember		  
Not earning a return, asset 5,804us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_DeferredMaintenanceCostsMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_DeferredMaintenanceCostsMember		  
Total, asset 5,804us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_DeferredMaintenanceCostsMember		 5,813us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_DeferredMaintenanceCostsMember
Power Deferrals Regulatory Asset [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 8,291ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_PowerDeferralsRegulatoryAssetMember		  
Not earning a return, asset 0us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_PowerDeferralsRegulatoryAssetMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_PowerDeferralsRegulatoryAssetMember		  
Total, asset 8,291us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_PowerDeferralsRegulatoryAssetMember		 5,065us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_PowerDeferralsRegulatoryAssetMember
Regulatory Asset For Interest Rate Swaps [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetForInterestRateSwapsMember		 [1]  
Not earning a return, asset 77,063us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetForInterestRateSwapsMember		 [1]  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetForInterestRateSwapsMember		 [1]  
Total, asset 77,063us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetForInterestRateSwapsMember		 [1] 0us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_RegulatoryAssetForInterestRateSwapsMember		 [1]
Non Current Regulatory Asset For Utility Derivatives [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 0ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= ava_NonCurrentRegulatoryAssetForUtilityDerivativesMember		  
Not earning a return, asset 24,483us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= ava_NonCurrentRegulatoryAssetForUtilityDerivativesMember		  
Pending regulatory treatment, asset 0us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= ava_NonCurrentRegulatoryAssetForUtilityDerivativesMember		  
Total, asset 24,483us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_NonCurrentRegulatoryAssetForUtilityDerivativesMember		 23,258us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ava_NonCurrentRegulatoryAssetForUtilityDerivativesMember
Other Regulatory Assets [Member]    
Regulated Asset Liability [Line Items]    
Earning a return, asset 2,879ava_RegulatoryAssetEarningReturn
/ us-gaap_RegulatoryAssetAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember		  
Not earning a return, asset 5,663us-gaap_RemainingAmountsOfRegulatoryAssetsForWhichNoReturnOnInvestmentDuringRecoveryPeriodIsProvided
/ us-gaap_RegulatoryAssetAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember		  
Pending regulatory treatment, asset 4,496us-gaap_AmountOfRegulatoryCostsNotYetApproved
/ us-gaap_RegulatoryAssetAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember		  
Total, asset $ 13,038us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember		 $ 13,282us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Minimum [Member] | Regulatory Liability for Interest Rate Swaps [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory liability 2014  
Maximum [Member] | Regulatory Liability for Interest Rate Swaps [Member]    
Regulated Asset Liability [Line Items]    
Remaining amortization period, regulatory liability 2015  
[1] For interest rate swap agreements, each period Avista Utilities records all mark-to-market gains and losses as assets and liabilities and records offsetting regulatory assets and liabilities, such that there is no income statement impact. This is similar to the treatment of energy commodity derivatives described above. Upon settlement of interest rate swaps, the regulatory asset or liability (included as part of long-term debt) is amortized as a component of interest expense over the term of the associated debt.