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REGULATORY MATTERS: Regulatory Assets and Liabilities Table (Details) - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets $ 1,564,458 $ 1,507,372
Regulatory Liabilities 1,052,151 984,326
Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1] 505,302  
Regulatory Liabilities [1] 415,343  
Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 1,059,156  
Regulatory Liabilities 636,808  
Income taxes    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [2] 121,489 127,634
Income taxes | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[2] 0  
Income taxes | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [2] 121,489  
Depreciation-related excess deferred income taxes    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [3] 128,180 137,903
Depreciation-related excess deferred income taxes | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[3] 128,180  
Depreciation-related excess deferred income taxes | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [3] 0  
Removal costs    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [4] 162,652 166,181
Removal costs | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[4] 0  
Removal costs | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [4] 162,652  
Investment tax credits    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 235,724 230,322
Investment tax credits | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1] 0  
Investment tax credits | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 235,724  
Deferred revenue-AFUDC    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [5] 280,979 250,942
Deferred revenue-AFUDC | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[5] 224,083  
Deferred revenue-AFUDC | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [5] 56,896  
Energy efficiency regulatory liability    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 16,493 9,277
Energy efficiency regulatory liability | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1] 16,493  
Energy efficiency regulatory liability | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 0  
Power supply costs    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [6] 42,419 3,949
Power supply costs | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[6] 42,419  
Power supply costs | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [6] 0  
Tax reform accrual for future amortization    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [7] 44,423 42,266
Tax reform accrual for future amortization | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[7] 0  
Tax reform accrual for future amortization | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [7] 44,423  
Other regulatory assets (liabilities)    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 8,007 15,852
Other regulatory assets (liabilities) | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1] 4,168  
Other regulatory assets (liabilities) | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 3,839  
Unfunded postretirement benefits    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [8] 11,785 0
Unfunded postretirement benefits | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[8] 0  
Unfunded postretirement benefits | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [8] 11,785  
Income taxes    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [9] 821,346 811,054
Income taxes | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[9] 0  
Income taxes | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [9] 821,346  
Unfunded postretirement benefits    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [8] 0 18,824
Unfunded postretirement benefits | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[8] 0  
Unfunded postretirement benefits | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [8] 0  
Pension expense deferrals    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [10] 247,340 252,197
Pension expense deferrals | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[10] 245,508  
Pension expense deferrals | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [10] 1,832  
Power supply costs    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 0 18,507
Power supply costs | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[6] 0  
Power supply costs | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 0  
Fixed cost adjustment    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Asset, Net [6] 6,855 17,761
Fixed cost adjustment | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Asset, Net [1],[6] 8,205  
Fixed cost adjustment | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Asset, Net [6] (1,350)  
Valmy Plant settlements    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 83,941 80,767
Valmy Plant settlements | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[6] 83,941  
Valmy Plant settlements | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 0  
Jim Bridger Plant    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 164,660 147,451
Jim Bridger Plant | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[6] 151,739  
Jim Bridger Plant | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 12,921  
Wildfire Mitigation Plan Deferral    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 91,670 63,966
Wildfire Mitigation Plan Deferral | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[6] 0  
Wildfire Mitigation Plan Deferral | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 91,670  
Asset retirement obligation    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [4] 62,166 37,842
Asset retirement obligation | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[4] 0  
Asset retirement obligation | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [4] 62,166  
Long-term service agreement    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 18,639 19,796
Long-term service agreement | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1] 11,313  
Long-term service agreement | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 7,326  
Other regulatory assets (liabilities)    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 18,321 11,089
Other regulatory assets (liabilities) | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1] 4,596  
Other regulatory assets (liabilities) | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 13,725  
Mark to Market liabilities    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [11] 49,520 $ 28,118
Mark to Market liabilities | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[11] 0  
Mark to Market liabilities | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [11] $ 49,520  
[1] Earning a return includes either interest or a return on the investment as a component of rate base at the allowed rate of return. The interest rate on deferral accounts is published annually by the IPUC and OPUC. The applicable rates for 2025 were 5.0% and 4.5%, respectively.
[2] Represents the tax gross-up related to the depreciation-related excess deferred income taxes and investment tax credits included in this table and has a corresponding deferred tax asset disclosed in Note 2 - "Income Taxes."
[3] For depreciation-related temporary differences under the normalized tax accounting method, the resulting excess deferred taxes will flow back to customers ratably over the remaining regulatory lives of Idaho Power's plant assets under the alternative method provided in the statute.
[4] Asset retirement obligations and removal costs are discussed in Note 14 - "Asset Retirement Obligations (ARO)."
[5] Idaho Power is collecting revenue in the Idaho jurisdiction for AFUDC on HCC relicensing costs but is deferring revenue recognition of the amounts collected until the license is issued and the asset is placed in service under the new license.
[6] This item is discussed in more detail in this Note 3 - "Regulatory Matters."
[7] Represents amount accrued under the May 2018 Idaho tax reform settlement stipulation (described below) for the future amortization of existing or future unspecified regulatory deferrals that would otherwise be a future liability recoverable from Idaho customers.
[8] Represents the unfunded obligation of Idaho Power’s pension and postretirement benefit plans, which are discussed in Note 12 - "Benefit Plans."
[9] Represents flow-through income tax accounting differences which have a corresponding deferred tax liability disclosed in Note 2 - "Income Taxes."
[10] Idaho Power records a regulatory asset for the difference between net periodic pension cost and pension cost considered for rate-making purposes relating to Idaho Power's defined benefit pension plan. In its Idaho jurisdiction, Idaho Power’s inclusion of pension costs for the establishment of retail rates is based upon contributions made to the pension plan. This regulatory asset account represents the difference between cumulative cash contributions and amounts collected in rates. Deferred costs are amortized into expense as the amounts are provided for in Idaho retail revenues.
[11] This item is discussed in more detail in Note 16 - "Derivative Financial Instruments."