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Derivatives And Risk Management (Interest Rate Swap Agreements) (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) Caontracts	Dec. 31, 2017 USD ($) Caontracts	Dec. 31, 2016 USD ($) Caontracts
Derivatives, Fair Value [Line Items]
Secured Debt		$ 1,786,700	$ 1,696,700
Derivative, Fair Value, Amount Offset Against Collateral, Net		62,408	44,758
Payments for (proceeds from) derivative instrument operating activities	$ (8,800)
Interest Rate Swap Agreements [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net		$ 34,970	$ 34,900
2017 | Interest Rate Swap Agreements [Member]
Derivatives, Fair Value [Line Items]
Number of interest rate swaps settled | Caontracts	5
Number of contracts | Caontracts			6
Derivative, Notional Amount			$ 75,000
Derivative, Maturity Date			Dec. 31, 2017
Settled derivative notional amount	$ 60,000
2018 | Interest Rate Swap Agreements [Member]
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts		14	14
Derivative, Notional Amount		$ 275,000	$ 275,000
Derivative, Maturity Date		Dec. 31, 2018	Dec. 31, 2018
2019 | Interest Rate Swap Agreements [Member]
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts		6	6
Derivative, Notional Amount		$ 70,000	$ 70,000
Derivative, Maturity Date		Dec. 31, 2019	Dec. 31, 2019
2020 | Interest Rate Swap Agreements [Member]
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts		3	2
Derivative, Notional Amount		$ 30,000	$ 20,000
Derivative, Maturity Date		Dec. 31, 2020	Dec. 31, 2020
2021 | Interest Rate Swap Agreements [Member]
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts		1
Derivative, Notional Amount		$ 15,000
Derivative, Maturity Date		Dec. 31, 2021
2022 | Interest Rate Swap Agreements [Member]
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts		5	5
Derivative, Notional Amount		$ 60,000	$ 60,000
Derivative, Maturity Date		Dec. 31, 2022	Dec. 31, 2022
Avista Utilities [Member]
Derivatives, Fair Value [Line Items]
Secured Debt		$ 1,711,700	$ 1,621,700
Avista Utilities [Member] | 2047 3.91% | First Mortgage [Member]
Derivatives, Fair Value [Line Items]
Secured Debt		$ 90,000	$ 0

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Number of interest rate swaps settled

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Settled derivative notional amount

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Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=d3e41678-113959

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Number of interest rate derivative instruments held by the entity at the reporting date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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