Long-Term Debt and Capital Leases Long-Term Debt and Capital Leases (Schedule of Long-Term Debt Instruments) (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent	$ (83,700)	$ (83,700)
Interest Rate at End of Period	2.08%	1.81%
Secured Debt	$ 1,696,700	$ 1,696,700
Secured and Unsecured Debt	1,711,700	1,711,700
Capital Lease Obligations	63,791	65,435
Debt Instrument, Unamortized Discount	(709)	(792)
Unamortized Debt Issuance Expense	(10,204)	(10,639)
Long-Term Debt, Before Current Portion And Bonds Held by Company	1,764,578	1,765,704
Long-term Debt and Capital Lease Obligations, Current	(277,814)	(3,287)
Long-term debt and capital leases	$ 1,403,064	$ 1,678,717
Minimum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	1.81%	1.29%
Maximum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	2.08%	1.81%
Avista Utilities [Member]
Debt Instrument [Line Items]
Secured Debt	$ 1,621,700	$ 1,621,700
Avista Utilities [Member] \| First Mortgage [Member] \| 2018 5.95%
Debt Instrument [Line Items]
Maturity Year	2018
Interest Rate at End of Period	5.95%
Secured Debt	$ 250,000	250,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2019
Debt Instrument [Line Items]
Maturity Year	2019
Interest Rate at End of Period	5.45%
Secured Debt	$ 90,000	90,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2020
Debt Instrument [Line Items]
Maturity Year	2020
Interest Rate at End of Period	3.89%
Secured Debt	$ 52,000	52,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2022
Debt Instrument [Line Items]
Maturity Year	2022
Interest Rate at End of Period	5.13%
Secured Debt	$ 250,000	250,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2035
Debt Instrument [Line Items]
Maturity Year	2035
Interest Rate at End of Period	6.25%
Secured Debt	$ 150,000	150,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2037
Debt Instrument [Line Items]
Maturity Year	2037
Interest Rate at End of Period	5.70%
Secured Debt	$ 150,000	150,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2040
Debt Instrument [Line Items]
Maturity Year	2040
Interest Rate at End of Period	5.55%
Secured Debt	$ 35,000	35,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2041
Debt Instrument [Line Items]
Maturity Year	2041
Interest Rate at End of Period	4.45%
Secured Debt	$ 85,000	85,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2044
Debt Instrument [Line Items]
Maturity Year	2044
Interest Rate at End of Period	4.11%
Secured Debt	$ 60,000	60,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2045
Debt Instrument [Line Items]
Maturity Year	2045
Interest Rate at End of Period	4.37%
Secured Debt	$ 100,000	100,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2047
Debt Instrument [Line Items]
Maturity Year	2047
Interest Rate at End of Period	4.23%
Secured Debt	$ 80,000	80,000
Avista Utilities [Member] \| First Mortgage [Member] \| 2051
Debt Instrument [Line Items]
Maturity Year	2051
Interest Rate at End of Period	3.54%
Secured Debt	$ 175,000	175,000
Avista Utilities [Member] \| Secured Debt [Member] \| 2018 7.39% to 7.45%
Debt Instrument [Line Items]
Maturity Year	2018
Medium-term Notes, Noncurrent	$ 22,500	22,500
Avista Utilities [Member] \| Secured Debt [Member] \| 2018 7.39% to 7.45% \| Minimum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	7.39%
Avista Utilities [Member] \| Secured Debt [Member] \| 2018 7.39% to 7.45% \| Maximum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	7.45%
Avista Utilities [Member] \| Secured Debt [Member] \| 2023 7.18% to 7.54%
Debt Instrument [Line Items]
Maturity Year	2023
Medium-term Notes, Noncurrent	$ 13,500	13,500
Avista Utilities [Member] \| Secured Debt [Member] \| 2028
Debt Instrument [Line Items]
Maturity Year	2028
Medium-term Notes, Noncurrent	$ 25,000	25,000
Interest Rate at End of Period	6.37%
Avista Utilities [Member] \| Secured Debt [Member] \| 2032
Debt Instrument [Line Items]
Maturity Year	2032
Long-term Pollution Control Bond, Noncurrent	$ 66,700	66,700
Avista Utilities [Member] \| Secured Debt [Member] \| 2034
Debt Instrument [Line Items]
Maturity Year	2034
Long-term Pollution Control Bond, Noncurrent	$ 17,000	17,000
Avista Utilities [Member] \| Secured Debt [Member] \| Two Thousand Twenty Three Seven Point One Eight Percentage To Seven Point Five Four Percentage [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	7.18%
Avista Utilities [Member] \| Secured Debt [Member] \| Two Thousand Twenty Three Seven Point One Eight Percentage To Seven Point Five Four Percentage [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	7.54%
Alaska Electric Light & Power [Member] \| First Mortgage [Member] \| 2044
Debt Instrument [Line Items]
Maturity Year	2044
Interest Rate at End of Period	4.54%
Secured Debt	$ 75,000	75,000
Alaska Energy Resources Company [Member] \| Unsecured Debt [Member] \| 2019
Debt Instrument [Line Items]
Maturity Year	2019
Interest Rate at End of Period	3.85%
Unsecured Debt	$ 15,000	$ 15,000

Long-Term Debt, Before Current Portion And Bonds Held by Company

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Secured and Unsecured Debt

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

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Amount, after accumulated amortization, of debt discount.

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Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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Noncurrent portion of a debt security issued by a state, certain agencies or authorities, a local government, or development corporation to finance the construction of air- or water-pollution control facilities or sewage or solid waste disposal facilities pursuant to federal law. The bonds are backed by the credit of the beneficiary of the financing rather than the credit of the issuer.

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Carrying value at the balance sheet date of the noncurrent portion of a financial instrument used to receive debt funding on a regular basis with original maturities ranging from 5-10 years.

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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.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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