Business Acquisitions Pro Forma Operating Results (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	21 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015
Business Acquisition [Line Items]
Revenues Excluding Acquired Entity	$ 433,699ava_RevenuesExcludingAcquiredEntity	$ 446,578ava_RevenuesExcludingAcquiredEntity
Supplemental Pro Forma Revenues	446,490us-gaap_Revenues	446,578us-gaap_Revenues
Business Acquisition, Pro Forma Revenue	446,490	459,764
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	12,791	0
Income (Loss) from Continuing Operations Attributable to Parent	43,918	47,476
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	0	1,023
Net income attributable to Avista Corporation shareholders	46,449us-gaap_NetIncomeLoss	48,499us-gaap_NetIncomeLoss
Business Acquisition, Pro Forma Net Income (Loss)	46,454	52,049
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	2,531	0
Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Supplemental Pro Forma Revenues	12,791	13,186
Net income attributable to Avista Corporation shareholders	2,531	3,256
Avista Utilities [Member]
Business Acquisition [Line Items]
Supplemental Pro Forma Revenues	424,083	437,574
Business Combination, Acquisition Related Costs			3,000
Net income attributable to Avista Corporation shareholders	44,384	47,996
Avista Utilities [Member] \| Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs	5	294
Acquisition-related Costs [Member] \| Avista Utilities [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs			$ 400

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Revenues Excluding Acquired Entity

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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Amount of income (loss) from a disposal group, net of income tax, reported as a separate component of income before extraordinary items after deduction or consideration of the amount allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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