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Committed Lines of Credit (Details) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Apr. 30, 2014
Jul. 01, 2014
Short-term Debt [Line Items]        
Line of Credit, Current $ 65,000,000us-gaap_LinesOfCreditCurrent $ 105,000,000us-gaap_LinesOfCreditCurrent    
Avista Utilities [Member]        
Short-term Debt [Line Items]        
Line of Credit, Current 65,000,000us-gaap_LinesOfCreditCurrent
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AvistaUtilitiesMember
105,000,000us-gaap_LinesOfCreditCurrent
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AvistaUtilitiesMember
   
Letters of credit outstanding at end of period 35,579,000us-gaap_LettersOfCreditOutstandingAmount
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AvistaUtilitiesMember
32,579,000us-gaap_LettersOfCreditOutstandingAmount
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AvistaUtilitiesMember
   
Average interest rate at end of period 0.94%us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AvistaUtilitiesMember
0.93%us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AvistaUtilitiesMember
   
Alaska Electric Light & Power [Member]        
Short-term Debt [Line Items]        
Line of Credit, Current 0us-gaap_LinesOfCreditCurrent
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AlaskaElectricLightPowerMember
0us-gaap_LinesOfCreditCurrent
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AlaskaElectricLightPowerMember
   
Line of Credit [Member] | Avista Utilities [Member]        
Short-term Debt [Line Items]        
Line of Credit Facility, Maximum Borrowing Capacity     400,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AvistaUtilitiesMember
 
Line of Credit [Member] | Alaska Electric Light & Power [Member]        
Short-term Debt [Line Items]        
Line of Credit Facility, Maximum Borrowing Capacity       $ 25,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_LineOfCreditMember
/ us-gaap_StatementBusinessSegmentsAxis
= ava_AlaskaElectricLightPowerMember