XML 103 R93.htm IDEA: XBRL DOCUMENT v2.4.1.9
Pension Plans And Other Postretirement Benefit Plans (Changes In Level 3 Assets) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 27.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember		 47.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember		  
Debt Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 58.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_DebtSecuritiesMember		 31.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_DebtSecuritiesMember		  
Absolute Return [Member] | Partnership And Closely Held Investments [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of beginning of year 34,151us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 17,755us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		  
Realized gains 0us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 0us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		  
Unrealized gains (losses) 1,963us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 2,396us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		  
Purchases, net 0us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 14,000us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		  
Fair value of plan assets as of end of year 36,114us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 34,151us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		  
Real Estate [Member] | Common/Collective Trusts [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of beginning of year 19,735us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 17,596us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Realized gains 24us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 0us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Unrealized gains (losses) 1,097us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 2,139us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Purchases, net 447us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 0us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Fair value of plan assets as of end of year 21,303us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 19,735us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Real Estate [Member] | Partnership And Closely Held Investments [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of beginning of year 3,873us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Realized gains 595us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 0us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Unrealized gains (losses) (644)us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 113us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Purchases, net 2,936us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 3,760us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Fair value of plan assets as of end of year 6,760us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 3,873us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Private Equity Funds [Member] | Partnership And Closely Held Investments [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of beginning of year 377us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		 660us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		  
Realized gains 0us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		 (323)us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		  
Unrealized gains (losses) (304)us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		 345us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		  
Purchases, net 0us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		 (305)us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		  
Fair value of plan assets as of end of year 73us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		 377us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_PrivateEquityFundsMember		  
Other Post-Retirement Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of beginning of year     25,288us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Fair value of plan assets as of end of year 31,312us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember		 29,732us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember		 25,288us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Other Post-Retirement Benefits [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		  
Other Post-Retirement Benefits [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 60.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember		 60.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember		  
Other Post-Retirement Benefits [Member] | Debt Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 40.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_DebtSecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember		 40.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_DebtSecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember		  
Pension Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of beginning of year     406,061us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Fair value of plan assets as of end of year 539,311us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember		 481,502us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember		 406,061us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Pension Benefits [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of end of year 64,250us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 58,136us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		  
Pension Benefits [Member] | Absolute Return [Member] | Partnership And Closely Held Investments [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of end of year 36,114us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 34,151us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 [1]  
Pension Benefits [Member] | Absolute Return [Member] | Partnership And Closely Held Investments [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of end of year 36,114us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 34,151us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_PartnershipAndCloselyHeldInvestmentsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_InvestmentTypeAxis
= ava_AbsoluteReturnMember		 [1]  
Pension Benefits [Member] | Real Estate [Member] | Common/Collective Trusts [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of end of year 21,303us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		 19,735us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_RealEstateMember		  
Pension Benefits [Member] | Real Estate [Member] | Common/Collective Trusts [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of end of year 21,303us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ava_CommonAndCollectiveTrustsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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Pension Benefits [Member] | Real Estate [Member] | Partnership And Closely Held Investments [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets as of end of year 6,760us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Pension Benefits [Member] | Real Estate [Member] | Partnership And Closely Held Investments [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
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Pension Benefits [Member] | Private Equity Funds [Member] | Partnership And Closely Held Investments [Member]      
Defined Benefit Plan Disclosure [Line Items]      
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Pension Benefits [Member] | Private Equity Funds [Member] | Partnership And Closely Held Investments [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
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[1] This category invests in multiple strategies to diversify risk and reduce volatility. The strategies include: (a) event driven, relative value, convertible, and fixed income arbitrage, (b) distressed investments, (c) long/short equity and fixed income, and (d) market neutral strategies.
[2] This category includes private equity funds that invest primarily in U.S. companies.