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Summary Of Significant Accounting Policies (Asset Retirement Obligations) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligations [Abstract]
Regulatory liability for utility plant retirement costs	$ 285,786	$ 273,983

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- Definition

Asset Retirement Obligations [Abstract]

+ References

No definition available.

+ Details

Name:	ava_AssetRetirementObligationsAbstract
Namespace Prefix:	ava_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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- Definition

Utility plant retirement costs recovered through rates charged to customers as a portion of depreciation expense. These costs do not represent legal or contractual obligations.

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No definition available.

+ Details

Name:	ava_RegulatoryLiabilityForUtilityPlantRetirementCostsNoncurrent
Namespace Prefix:	ava_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant