Number of Interest Rate Swaps Settled

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- Definition

Payments for (proceeds from) derivative instrument operating activities.

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- Definition

Settled Derivative Notional Amount

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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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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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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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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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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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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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Long-Term Debt - Schedule Of Long-Term Debt Instruments (Parenthetical) (Details)	1 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Contract	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Apr. 30, 2014 USD ($)
Debt Instrument [Line Items]
Secured Debt		$ 2,092,200,000	$ 1,979,200,000
Payments for (proceeds from) derivative instrument operating activities		33,499,000	13,325,000	$ 32,174,000
Avista Utilities [Member]
Debt Instrument [Line Items]
Secured Debt		2,017,200,000	1,904,200,000
Line of credit facility, maximum borrowing capacity					$ 400,000,000.0
2032 \| Secured Debt [Member]
Debt Instrument [Line Items]
Pollution Control Bonds		66,700,000
2032 \| Secured Debt [Member] \| Avista Utilities [Member]
Debt Instrument [Line Items]
Pollution Control Bonds		$ 66,700,000	66,700,000
Maturity Year		2032
2034 \| Secured Debt [Member]
Debt Instrument [Line Items]
Pollution Control Bonds		$ 17,000,000.0
2034 \| Secured Debt [Member] \| Avista Utilities [Member]
Debt Instrument [Line Items]
Pollution Control Bonds		$ 17,000,000	17,000,000
Maturity Year		2034
2050 3.07% \| Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 400,000,000.0
2050 3.07% \| First Mortgage [Member] \| Avista Utilities [Member]
Debt Instrument [Line Items]
Secured Debt		$ 165,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.07%
Maturity Year		2050
2019 \| First Mortgage [Member] \| Avista Utilities [Member]
Debt Instrument [Line Items]
Repayments of debt	$ 52,000,000.0
2020 [Member] \| First Mortgage [Member]
Debt Instrument [Line Items]
Number of interest rate swaps settled \| Contract		7
Settled derivative notional amount		$ 70,000,000.0
2020 [Member] \| First Mortgage [Member] \| Avista Utilities [Member]
Debt Instrument [Line Items]
Secured Debt			$ 52,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.89%
Maturity Year		2020