Balance Sheet Components - Schedule of Regulatory Assets and Liabilities (Parenthetical) (Details) $ in Millions	9 Months Ended
Sep. 30, 2021 USD ($)
Regulated Asset Liability [Line Items]
Change to flow-through tax treatment of certain basis adjustments	$ 128.8

Increase decrease in flow-through tax treatment of certain basis adjustments.

No definition available.

Name:	ava_IncreaseDecreaseInFlowThroughTaxTreatmentOfCertainBasisAdjustments
Namespace Prefix:	ava_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration