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v3.20.2

Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions | 9 Months Ended
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Sep. 30, 2020 USD ($)
COVID-19 |
Accounting Policies [Line Items] |
Deferred incremental bad debt expense | $ 2.5

X
- Definition Accounting policies. + References No definition available. + Details
Name: | ava_AccountingPoliciesLineItems
Namespace Prefix: | ava_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Deferred incremental bad debt expense. + References No definition available. + Details
Name: | ava_DeferredIncrementalBadDebtExpense
Namespace Prefix: | ava_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_UnusualOrInfrequentItemAxis=ava_COVID19Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |