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Stock Compensation Plans (Narrative) (Details) (USD $)
In Thousands, except Share data in Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense $ 6,007us-gaap_AllocatedShareBasedCompensationExpense $ 5,037us-gaap_AllocatedShareBasedCompensationExpense $ 4,549us-gaap_AllocatedShareBasedCompensationExpense
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years    
Weighted average remaining contractual terms 0 years 8 months 11 days    
Unrecognized compensation expense 1,349us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
1,199us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
1,428us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Total Shareholder Return Market-Based Awards and Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense 1,300us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= ava_TotalShareholderReturnMarketBasedAwardsandPerformanceAwardsMember
900us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= ava_TotalShareholderReturnMarketBasedAwardsandPerformanceAwardsMember
 
Award vesting period 3 years    
Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average remaining contractual terms 2 years    
Unrecognized compensation expense 1,577us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
0us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
0us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Total Shareholder Return Market-Based Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average remaining contractual terms 1 year 5 months    
Unrecognized compensation expense $ 2,833us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= ava_TotalShareholderReturnMarketBasedAwardsMember
$ 3,651us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= ava_TotalShareholderReturnMarketBasedAwardsMember
$ 3,800us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= ava_TotalShareholderReturnMarketBasedAwardsMember
1998 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 4.5us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= ava_NineteenNinetyEightPlanMember
   
Common stock, shares available for grant 0.4us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_AwardTypeAxis
= ava_NineteenNinetyEightPlanMember
   
2000 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 2.5us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= ava_TwoThousandPlanMember
   
Common stock, shares available for grant 1.9us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_AwardTypeAxis
= ava_TwoThousandPlanMember
   
Maximum [Member] | Total Shareholder Return Market-Based Awards and Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock issued range, percent of the performance shares granted 200.00%ava_CommonStockIssuedRangePercentOfPerformanceSharesGranted
/ us-gaap_AwardTypeAxis
= ava_TotalShareholderReturnMarketBasedAwardsandPerformanceAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
   
Minimum [Member] | Total Shareholder Return Market-Based Awards and Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock issued range, percent of the performance shares granted 0.00%ava_CommonStockIssuedRangePercentOfPerformanceSharesGranted
/ us-gaap_AwardTypeAxis
= ava_TotalShareholderReturnMarketBasedAwardsandPerformanceAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember