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Commitments and Contingencies - Additional Information (Details) $ in Millions |  | 1 Months Ended | 2 Months Ended | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 15, 2025 Employees Chapter | Jun. 30, 2025 USD ($) Plaintiff | Aug. 31, 2019 USD ($) | May 31, 2025 USD ($) | Jun. 30, 2025 USD ($) Lawsuit Plaintiff | Jul. 31, 2024 | Aug. 31, 2023 a | Jan. 16, 2023 | Sep. 30, 2020 a Structures
Collective Bargaining Agreements Avista Utilities Employees [Member] | IBEW [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Percentage of employees represented |  |  |  |  | 35.00% |  |  |  |
Collective Bargaining Agreements Avista Utilities Bargaining Unit Employees [Member] | IBEW [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Percentage of largest group of employees represented |  |  |  |  | 90.00% |  |  |  |
Collective Bargaining Agreements [Member] | IBEW [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
IBEW chapter | Chapter | 77 |  |  |  |  |  |  |  |
Agreement term |  |  |  |  | 4 years |  |  |  |
Agreement expiration month and year |  |  |  |  | 2025-03 |  |  |  |
Number of employees comprised | Employees | 20 |  |  |  |  |  |  |  |
Boyds Fire [Member] | Asplundh Tree Company and CN Utility Consulting [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Litigation settlement amount |  | $ 3.0 |  |  |  |  |  |  |
Boyds Fire [Member] | Avista Corp [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Litigation settlement amount |  | $ 0.1 |  |  |  |  |  |  |
Boyds Fire [Member] | Damage from Fire [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value |  |  | $ 4.0 |  |  |  |  |  |
Boyds Fire [Member] | Property Damages [Member] | Avista Corp [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value |  |  | 1.0 |  |  |  |  |  |
Boyds Fire [Member] | Insurance proceeds paid to their insureds [Member] | Avista Corp [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value |  |  | $ 2.0 |  |  |  |  |  |
Babb Road Fire [Member] | Damage from Fire [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Litigation settlement amount |  |  |  | $ 27.0 |  |  |  |  |
Number of residential, commercial and other structures impacted | Structures |  |  |  |  |  |  |  |  | 220
Road fire covered area | a |  |  |  |  |  |  |  |  | 15,000
Number of subrogation actions filed | Lawsuit |  |  |  |  | 6 |  |  |  |
Number of actions on behalf of individual plaintiffs | Plaintiff |  |  |  |  | 5 |  |  |  |
Number Of Plaintiffs | Plaintiff |  | 128 |  |  | 128 |  |  |  |
Babb Road Fire [Member] | Damage from Fire [Member] | CN Utility Consulting [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Litigation settlement amount |  |  |  | 6.0 |  |  |  |  |
Babb Road Fire [Member] | Damage from Fire [Member] | Avista Corp [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Litigation settlement amount |  |  |  | $ 21.0 |  |  |  |  |
Orofino Fire [Member] | Damage from Fire [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Road fire covered area | a |  |  |  |  |  |  | 53 |  |
Colstrip [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Settlement Amount |  |  |  |  | $ 1.0 |  |  |  |
Colstrip [Member] | PSE [Member] | Unit 4 [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Owners percentage interest |  | 25.00% |  |  | 25.00% | 25.00% |  |  |
Colstrip [Member] | NorthWestern [Member] | Unit 4 [Member] |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Owners percentage interest |  | 30.00% |  |  | 30.00% |  |  | 15.00% |

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