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Long-Term Debt (Narrative) (Details) (USD $)
 0 Months Ended 12 Months Ended
Dec. 31, 1998
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Debt Instrument [Line Items]        
Long-term Pollution Control Bond, Noncurrent   $ (83,700,000)us-gaap_LongTermPollutionControlBond [1],[2] $ (83,700,000)us-gaap_LongTermPollutionControlBond [1],[2]  
Secured Debt   1,511,700,000us-gaap_SecuredDebt 1,376,700,000us-gaap_SecuredDebt  
Debt instrument, interest rate, stated percentage 8.45%us-gaap_DebtInstrumentInterestRateStatedPercentage 1.11%us-gaap_DebtInstrumentInterestRateStatedPercentage 1.11%us-gaap_DebtInstrumentInterestRateStatedPercentage 1.19%us-gaap_DebtInstrumentInterestRateStatedPercentage
Amount borrowed to acquire a long-term fixed rate electric capacity contract 145,000,000ava_AmountBorrowedToAcquireLongTermFixedRateElectricCapacityContract      
Funds held in trust account which are used to secure long-term debt   1,600,000us-gaap_AssetsHeldInTrustNoncurrent    
Current portion of nonrecourse long-term debt of Spokane Energy   1,431,000us-gaap_OtherLongTermDebtCurrent 16,407,000us-gaap_OtherLongTermDebtCurrent  
2032 [Member] | Secured Debt [Member]        
Debt Instrument [Line Items]        
Long-term Pollution Control Bond, Noncurrent   66,700,000us-gaap_LongTermPollutionControlBond
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandThirtyTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		    
2034 [Member] | Secured Debt [Member]        
Debt Instrument [Line Items]        
Long-term Pollution Control Bond, Noncurrent   17,000,000us-gaap_LongTermPollutionControlBond
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandThirtyFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		    
Avista Corporation [Member]        
Debt Instrument [Line Items]        
Secured Debt   1,436,700,000us-gaap_SecuredDebt
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember		 1,376,700,000us-gaap_SecuredDebt
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember		  
Avista Corporation [Member] | First Mortgage [Member]        
Debt Instrument [Line Items]        
Amount of First Mortgage Bonds that Could be Issued, Percent   66.66%ava_AmountOfFirstMortgageBondsThatCouldBeIssuedPercent
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		    
Amount of first mortgage bonds that could be issued   1,000,000,000ava_AmountOfFirstMortgageBondsThatCouldBeIssued
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		    
Avista Corporation [Member] | 2032 [Member] | Secured Debt [Member]        
Debt Instrument [Line Items]        
Long-term Pollution Control Bond, Noncurrent   66,700,000us-gaap_LongTermPollutionControlBond
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandThirtyTwoMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		 [2] 66,700,000us-gaap_LongTermPollutionControlBond
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandThirtyTwoMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		 [2]  
Maturity Year   2032 [2]    
Avista Corporation [Member] | 2034 [Member] | Secured Debt [Member]        
Debt Instrument [Line Items]        
Long-term Pollution Control Bond, Noncurrent   17,000,000us-gaap_LongTermPollutionControlBond
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandThirtyFourMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		 [1] 17,000,000us-gaap_LongTermPollutionControlBond
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandThirtyFourMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SecuredDebtMember		 [1]  
Maturity Year   2034 [1]    
Avista Corporation [Member] | 2047 [Member] | First Mortgage [Member]        
Debt Instrument [Line Items]        
Secured Debt   80,000,000us-gaap_SecuredDebt
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= ava_AvistaCorporationMember
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= us-gaap_FirstMortgageMember		 80,000,000us-gaap_SecuredDebt
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= ava_TwoThousandFortySevenMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		  
Debt instrument, interest rate, stated percentage   4.23%us-gaap_DebtInstrumentInterestRateStatedPercentage
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= ava_TwoThousandFortySevenMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		    
Maturity Year   2047    
Avista Corporation [Member] | 2016 | First Mortgage [Member]        
Debt Instrument [Line Items]        
Secured Debt   90,000,000us-gaap_SecuredDebt
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/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		 90,000,000us-gaap_SecuredDebt
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandSixteenMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		  
Debt instrument, interest rate, stated percentage   0.84%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandSixteenMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		    
Maturity Year   2016    
Avista Corporation [Member] | Two Thousand Forty Four [Member] | First Mortgage [Member]        
Debt Instrument [Line Items]        
Secured Debt   60,000,000us-gaap_SecuredDebt
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandFortyFourMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		 [1]    
Debt instrument, interest rate, stated percentage   4.11%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandFortyFourMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		 [1]    
Maturity Year   2044 [1]    
Avista Corporation [Member] | 2019 [Member] | First Mortgage [Member]        
Debt Instrument [Line Items]        
Secured Debt   90,000,000us-gaap_SecuredDebt
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandNineteenMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		 90,000,000us-gaap_SecuredDebt
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandNineteenMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		  
Debt instrument, interest rate, stated percentage   5.45%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandNineteenMember
/ dei_LegalEntityAxis
= ava_AvistaCorporationMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		    
Maturity Year   2019    
Alaska Electric Light & Power [Member] | First Mortgage [Member]        
Debt Instrument [Line Items]        
Amount of First Mortgage Bonds that Could be Issued, Percent   66.66%ava_AmountOfFirstMortgageBondsThatCouldBeIssuedPercent
/ dei_LegalEntityAxis
= ava_AlaskaElectricLightPowerMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		    
Amount of first mortgage bonds that could be issued   0ava_AmountOfFirstMortgageBondsThatCouldBeIssued
/ dei_LegalEntityAxis
= ava_AlaskaElectricLightPowerMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		    
Alaska Electric Light & Power [Member] | Two Thousand Forty Four [Member] | First Mortgage [Member]        
Debt Instrument [Line Items]        
Secured Debt   75,000,000us-gaap_SecuredDebt
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandFortyFourMember
/ dei_LegalEntityAxis
= ava_AlaskaElectricLightPowerMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		 [3] 0us-gaap_SecuredDebt
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandFortyFourMember
/ dei_LegalEntityAxis
= ava_AlaskaElectricLightPowerMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		 [3]  
Debt instrument, interest rate, stated percentage   4.54%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= ava_TwoThousandFortyFourMember
/ dei_LegalEntityAxis
= ava_AlaskaElectricLightPowerMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FirstMortgageMember		 [3]    
Maturity Year   2044 [3]    
Alaska Energy Resources Company [Member] | 2019 [Member] | Unsecured Debt [Member]        
Debt Instrument [Line Items]        
Debt instrument, interest rate, stated percentage   3.85%us-gaap_DebtInstrumentInterestRateStatedPercentage
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= ava_AlaskaEnergyResourcesCompanyMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 [4]    
Maturity Year   2019 [4]    
Unsecured Debt   $ 15,000,000us-gaap_UnsecuredDebt
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/ dei_LegalEntityAxis
= ava_AlaskaEnergyResourcesCompanyMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 [4] $ 0us-gaap_UnsecuredDebt
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= ava_TwoThousandNineteenMember
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= ava_AlaskaEnergyResourcesCompanyMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		 [4]  
[1] In December 2014, Avista Corp. issued $60.0 million of first mortgage bonds to three institutional investors in a private placement transaction. The first mortgage bonds bear an interest rate of 4.11 percent and mature in 2044. The total net proceeds from the sale of the new bonds were used to repay a portion of the borrowings outstanding under the Company’s $400.0 million committed line of credit and for general corporate purposes.
[2] In December 2010, $66.7 million and $17.0 million of the City of Forsyth, Montana Pollution Control Revenue Refunding Bonds (Avista Corporation Colstrip Project) due in 2032 and 2034, respectively, which had been held by Avista Corp. since 2008 and 2009, respectively, were refunded by new bond issues (Series 2010A and Series 2010B). The new bonds were not offered to the public and were purchased by Avista Corp. due to market conditions. The Company expects that at a later date, subject to market conditions, these bonds may be remarketed to unaffiliated investors. So long as Avista Corp. is the holder of these bonds, the bonds will not be reflected as an asset or a liability on Avista Corp.'s Consolidated Balance Sheets.
[3] In September 2014, AEL&P issued $75.0 million of 4.54 percent first mortgage bonds due in 2044 to two institutional investors in the private placement market. The first mortgage bonds were issued under and in accordance with the AEL&P Mortgage and Deed of Trust, dated as of July 1, 2014.
[4] In December 2014, AERC issued a $15.0 million unsecured term loan note due in 2019 to a national cooperative bank. The term note bears an interest rate of 3.85 percent.