Fair Value (Quantitative Information) (Details) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($) $ / MWH MMBTU MWh $ / MmBtu	Dec. 31, 2017 USD ($)
Power Exchange Agreements [Member] \| Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Transaction/Delivery Volumes \| MWh	292,145
Average operation and maintenance charges \| $ / MWH	45.61
Minimum [Member] \| Power Exchange Agreements [Member] \| Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions Operation And Maintenance Charges \| $ / MWH	40.05
Maximum [Member] \| Power Exchange Agreements [Member] \| Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions Operation And Maintenance Charges \| $ / MWH	52.59
Fair Value, Measurements, Recurring [Member] \| Power Exchange Agreements [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Liability \| $	$ (5,909)	$ (13,245)
Fair Value, Measurements, Recurring [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Liability \| $	$ (3,004)	$ (3,164)
Sales [Member] \| Minimum [Member] \| Natural Gas Exchange Agreements [Member] \| Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price \| $ / MmBtu	1.46
Transaction/Delivery Volumes \| MMBTU	60,000
Sales [Member] \| Maximum [Member] \| Natural Gas Exchange Agreements [Member] \| Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price \| $ / MmBtu	3.21
Transaction/Delivery Volumes \| MMBTU	310,000
Purchase [Member] \| Minimum [Member] \| Natural Gas Exchange Agreements [Member] \| Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price \| $ / MmBtu	1.40
Transaction/Delivery Volumes \| MMBTU	125,000
Purchase [Member] \| Maximum [Member] \| Natural Gas Exchange Agreements [Member] \| Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price \| $ / MmBtu	1.83
Transaction/Delivery Volumes \| MMBTU	310,000

Fair Value Assumptions, Average Operation And Maintenance Charges

No definition available.

Name:	ava_FairValueAssumptionsAverageOperationAndMaintenanceCharges
Namespace Prefix:	ava_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair Value Assumptions, Operation And Maintenance Charges

+ References

No definition available.

+ Details

Name:	ava_FairValueAssumptionsOperationAndMaintenanceCharges
Namespace Prefix:	ava_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

The forward price on the price risk forward or futures contract, such as a gas futures contract.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeForwardPrice
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure
Namespace Prefix:	us-gaap_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ava_PowerExchangeAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=ava_SurrogateFacilityPricingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ava_NaturalGasExchangeAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_SalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=ava_InternallyDerivedWeightedAverageCostOfGasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=ava_PurchaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: