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Long-Term Debt - Schedule Of Long-Term Debt Instruments (Parenthetical) (Details) | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2021 USD ($) | Sep. 30, 2021 USD ($) | Dec. 31, 2021 USD ($) Contract | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Apr. 30, 2014 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |
Secured Debt | $ 2,232,200,000 |  | $ 2,232,200,000 | $ 2,092,200,000 |  |
Proceeds from issuance of long-term debt |  |  | 140,000,000 | 165,000,000 | $ 180,000,000 |
Avista Utilities [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Secured Debt | $ 2,157,200,000 |  | $ 2,157,200,000 | 2,017,200,000 |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  | $ 400,000,000.0
First Mortgage [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 8.00% |  | 8.00% |  |  |
2032 | Secured Debt [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Pollution Control Bonds | $ 66,700,000 |  | $ 66,700,000 |  |  |
2032 | Secured Debt [Member] | Avista Utilities [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Pollution Control Bonds | 66,700,000 |  | $ 66,700,000 | 66,700,000 |  |
Maturity Year |  |  | 2032 |  |  |
2034 | Secured Debt [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Pollution Control Bonds | 17,000,000.0 |  | $ 17,000,000.0 |  |  |
2034 | Secured Debt [Member] | Avista Utilities [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Pollution Control Bonds | 17,000,000 |  | $ 17,000,000 | 17,000,000 |  |
Maturity Year |  |  | 2034 |  |  |
2.90% Due in 2051 [Member] | Line of Credit [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | 400,000,000.0 |  | $ 400,000,000.0 |  |  |
2.90% Due in 2051 [Member] | First Mortgage [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Proceeds from issuance of long-term debt | 70,000,000.0 |  |  |  |  |
2.90% Due in 2051 [Member] | First Mortgage [Member] | Interest Rate Swap [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Number of interest rate swaps settled | Contract |  |  | 4 |  |  |
Notional Amount | 45,000,000.0 |  | $ 45,000,000.0 |  |  |
Net payments from settlement of derivatives |  |  | 17,200,000 |  |  |
2.90% Due in 2051 [Member] | First Mortgage [Member] | Avista Utilities [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Secured Debt | $ 140,000,000 |  | $ 140,000,000 |  |  |
Proceeds from issuance of long-term debt |  | $ 70,000,000.0 |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 2.90% | 2.90% | 2.90% |  |  |
Maturity Year |  | 2051 | 2051 |  |  |
2050 3.07% | First Mortgage [Member] | Avista Utilities [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Secured Debt | $ 165,000,000 |  | $ 165,000,000 | $ 165,000,000 |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.07% |  | 3.07% |  |  |
Maturity Year |  |  | 2050 |  |  |

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