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v3.20.4

Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Parenthetical) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($)
COVID-19 [Member] |
Summary Of Significant Accounting Policies [Line Items] |
Deferred incremental bad debt expense | $ 7.1

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- Definition Deferred incremental bad debt expense. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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Period Type: | duration

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- Definition Summary of significant accounting policies. + References No definition available. + Details
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Namespace Prefix: | ava_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |