Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	9 Months Ended	12 Months Ended
Jan. 31, 1999	Sep. 30, 2011 mW	Dec. 31, 2002
Variable Interest Entities [Abstract]
Evaluated power capacity of Lancaster project		270
Minimum estimated life of plant, in years		15
Maximum estimated life of plant, in years		25
Future contractual obligation		$ 346
Amounts borrowed from a funding trust	145.0
Cash received from monetization of the contract	143.4
Maturity date of loan from funding trust		Jan. 01, 2015
Amount of cash received fully amortized by 2002			$ 143.4

Amount of Cash Received Fully Amortized by Year End 2002

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Namespace Prefix:	ava
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Cash Received From Monetization Of The Contract

+ Details

Name:	ava_CashReceivedFromMonetizationOfContract
Namespace Prefix:	ava
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Evaluated Power Capacity

+ Details

Name:	ava_EvaluatedPowerCapacity
Namespace Prefix:	ava
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	duration

- Definition

Variable Interest Entities Disclosure [Abstract]

+ Details

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Namespace Prefix:	ava
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, collateralized financings, and capital lease obligations.

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date when the debt instrument is scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The maximum useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum useful life of long lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLifeMinimum
Namespace Prefix:	us-gaap
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph b

-URI http://asc.fasb.org/extlink&oid=6970148&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS140-4/FIN46(R)

-Paragraph C6

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6970148&loc=d3e5747-111685

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant