Summary Of Significant Accounting Policies (Other Income - Net) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Interest income	$ 987us-gaap_InvestmentIncomeInterest	$ 754us-gaap_InvestmentIncomeInterest	$ 944us-gaap_InvestmentIncomeInterest
Interest on regulatory deferrals	220ava_InterestOnRegulatoryDeferrals	126ava_InterestOnRegulatoryDeferrals	68ava_InterestOnRegulatoryDeferrals
Equity-related AFUDC	8,808	6,066	4,055
Net gain (loss) on investments	276us-gaap_GainLossOnInvestments	(3,378)us-gaap_GainLossOnInvestments	(3,343)us-gaap_GainLossOnInvestments
Other income	1,055us-gaap_OtherIncome	1,599us-gaap_OtherIncome	989us-gaap_OtherIncome
Other income-net	$ 11,346us-gaap_OtherNonoperatingIncomeExpense	$ 5,167us-gaap_OtherNonoperatingIncomeExpense	$ 2,713us-gaap_OtherNonoperatingIncomeExpense

Interest On Regulatory Deferrals

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- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

+ References

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-Topic 225

-SubTopic 10

-Section S99

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-Subparagraph (SX 210.5-03.7(c),9(a))

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-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Article 5

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- Definition

Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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-Name Regulation S-X (SX)

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-Subparagraph (SX 210.5-03.7(b))

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- Definition

Reflects the sum of all other revenue and income recognized by the entity in the period not otherwise specified in the income statement.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

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-Subparagraph (SX 210.7-04.4)

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The net amount of other income and expense amounts, the components of which are not separately disclosed on the income statement, resulting from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business) also known as other nonoperating income (expense) recognized for the period. Such amounts may include: (a) dividends, (b) interest on securities, (c) net gains or losses on securities, (d) unusual costs, (e) gains or losses on foreign exchange transactions, and (f) miscellaneous other income and expense items.

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The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

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