Long-Term Debt - Schedule Of Long-Term Debt Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Secured Debt	$ 2,092,200	$ 1,979,200
Secured and Unsecured Debt	2,107,200	1,994,200
Unamortized debt discount	(710)	(788)
Unamortized Debt Issuance Expense	(14,256)	(13,944)
Total	2,092,234	1,979,468
Current portion of long-term debt		(52,000)
Long-term debt	2,008,534	1,843,768
Secured Debt [Member]
Debt Instrument [Line Items]
Pollution Control Bonds	(83,700)	(83,700)
2032 \| Secured Debt [Member]
Debt Instrument [Line Items]
Pollution Control Bonds	66,700
2034 \| Secured Debt [Member]
Debt Instrument [Line Items]
Pollution Control Bonds	17,000
Avista Utilities [Member]
Debt Instrument [Line Items]
Secured Debt	$ 2,017,200	1,904,200
Avista Utilities [Member] \| 2020 [Member] \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2020
Debt Instrument, Interest Rate, Stated Percentage	3.89%
Secured Debt		52,000
Avista Utilities [Member] \| 2022 [Member] \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2022
Debt Instrument, Interest Rate, Stated Percentage	5.13%
Secured Debt	$ 250,000	250,000
Avista Utilities [Member] \| 2023 7.18% - 7.54% \| Secured Debt [Member]
Debt Instrument [Line Items]
Maturity Year	2023
Medium-Term Notes, Noncurrent	$ 13,500	13,500
Avista Utilities [Member] \| 2023 7.18% - 7.54% \| Minimum [Member] \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.18%
Avista Utilities [Member] \| 2023 7.18% - 7.54% \| Maximum [Member] \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.54%
Avista Utilities [Member] \| 2028 \| Secured Debt [Member]
Debt Instrument [Line Items]
Maturity Year	2028
Debt Instrument, Interest Rate, Stated Percentage	6.37%
Medium-Term Notes, Noncurrent	$ 25,000	25,000
Avista Utilities [Member] \| 2032 \| Secured Debt [Member]
Debt Instrument [Line Items]
Maturity Year	2032
Pollution Control Bonds	$ 66,700	66,700
Avista Utilities [Member] \| 2034 \| Secured Debt [Member]
Debt Instrument [Line Items]
Maturity Year	2034
Pollution Control Bonds	$ 17,000	17,000
Avista Utilities [Member] \| 2035 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2035
Debt Instrument, Interest Rate, Stated Percentage	6.25%
Secured Debt	$ 150,000	150,000
Avista Utilities [Member] \| 2037 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2037
Debt Instrument, Interest Rate, Stated Percentage	5.70%
Secured Debt	$ 150,000	150,000
Avista Utilities [Member] \| 2040 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2040
Debt Instrument, Interest Rate, Stated Percentage	5.55%
Secured Debt	$ 35,000	35,000
Avista Utilities [Member] \| 2041 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2041
Debt Instrument, Interest Rate, Stated Percentage	4.45%
Secured Debt	$ 85,000	85,000
Avista Utilities [Member] \| 2044 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2044
Debt Instrument, Interest Rate, Stated Percentage	4.11%
Secured Debt	$ 60,000	60,000
Avista Utilities [Member] \| 2045 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2045
Debt Instrument, Interest Rate, Stated Percentage	4.37%
Secured Debt	$ 100,000	100,000
Avista Utilities [Member] \| 2047 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2047
Debt Instrument, Interest Rate, Stated Percentage	4.23%
Secured Debt	$ 80,000	80,000
Avista Utilities [Member] \| 2047 3.91% \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2047
Debt Instrument, Interest Rate, Stated Percentage	3.91%
Secured Debt	$ 90,000	90,000
Avista Utilities [Member] \| 2048 4.35% \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2048
Debt Instrument, Interest Rate, Stated Percentage	4.35%
Secured Debt	$ 375,000	375,000
Avista Utilities [Member] \| 2049 3.43% \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2049
Debt Instrument, Interest Rate, Stated Percentage	3.43%
Secured Debt	$ 180,000	180,000
Avista Utilities [Member] \| 2050 3.07% \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2050
Debt Instrument, Interest Rate, Stated Percentage	3.07%
Secured Debt	$ 165,000
Avista Utilities [Member] \| 2051 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2051
Debt Instrument, Interest Rate, Stated Percentage	3.54%
Secured Debt	$ 175,000	175,000
Alaska Electric Light & Power [Member] \| 2044 \| First Mortgage [Member]
Debt Instrument [Line Items]
Maturity Year	2044
Debt Instrument, Interest Rate, Stated Percentage	4.54%
Secured Debt	$ 75,000	75,000
Alaska Energy Resources Company [Member] \| 2024 \| Unsecured Debt [Member]
Debt Instrument [Line Items]
Maturity Year	2024
Debt Instrument, Interest Rate, Stated Percentage	3.44%
Unsecured Debt	$ 15,000	$ 15,000

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

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- Definition

Secured and Unsecured Debt

+ References

No definition available.

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- Definition

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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No definition available.

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- Definition

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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- Definition

Amount, after accumulated amortization, of debt discount.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

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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- Definition

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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Amount of long-term debt classified as other, payable after one year or the operating cycle, if longer.

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- Definition

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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- Definition

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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