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REGULATORY MATTERS: Regulatory Assets and Liabilities Table (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets $ 1,653,050 $ 1,501,961
Regulatory Liabilities 882,553 860,601
Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1] 630,899  
Regulatory Liabilities [1] 336,964  
Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 1,022,151  
Regulatory Liabilities 545,589  
Income taxes    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [2] 108,641 94,946
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] 108,641  
Depreciation-related excess deferred income taxes    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [3] 147,950 158,634
Depreciation-related excess deferred income taxes | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[3] 147,950  
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] 175,369 180,087
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] 175,369  
Investment tax credits    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 165,479 115,285
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 165,479  
Deferred revenue-AFUDC    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [5] 228,671 207,528
Deferred revenue-AFUDC | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[5] 177,884  
Deferred revenue-AFUDC | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [5] 50,787  
Energy efficiency regulatory liability    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [6] 1,507 154
Energy efficiency regulatory liability | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[6] 1,507  
Energy efficiency regulatory liability | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [6] 0  
Power supply costs    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [7] 1,240 0
Power supply costs | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[7] 1,240  
Power supply costs | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [7] 0  
Mark to Market liabilities    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 88 59,544
Mark to Market liabilities | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1] 0  
Mark to Market liabilities | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 88  
Tax reform accrual for future amortization    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [8] 40,891 32,793
Tax reform accrual for future amortization | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1],[8] 0  
Tax reform accrual for future amortization | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [8] 40,891  
Other regulatory assets (liabilities)    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 12,717 11,630
Other regulatory assets (liabilities) | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities [1] 8,383  
Other regulatory assets (liabilities) | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Liabilities 4,334  
Income taxes    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [9] 774,672 739,689
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] 774,672  
Unfunded postretirement benefits    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [10] 87,318 70,254
Unfunded postretirement benefits | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[10] 0  
Unfunded postretirement benefits | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [10] 87,318  
Pension expense deferrals    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [11] 255,244 249,503
Pension expense deferrals | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[11] 253,744  
Pension expense deferrals | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [11] 1,500  
Energy efficiency regulatory asset    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 0 3,767
Energy efficiency regulatory asset | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[6] 0  
Energy efficiency regulatory asset | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [6] 0  
Power supply costs    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 115,525 129,309
Power supply costs | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[7] 134,816  
Power supply costs | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 19,291  
Fixed cost adjustment    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 51,285 41,901
Fixed cost adjustment | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[7] 36,037  
Fixed cost adjustment | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 15,248  
Valmy Plant settlements    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 82,917 90,747
Valmy Plant settlements | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[7] 82,917  
Valmy Plant settlements | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 0  
Jim Bridger Plant    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 123,632 80,531
Jim Bridger Plant | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[7] 108,376  
Jim Bridger Plant | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 15,256  
Wildfire Mitigation Plan Deferral    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 51,329 27,078
Wildfire Mitigation Plan Deferral | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1],[7] 0  
Wildfire Mitigation Plan Deferral | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [7] 51,329  
Asset retirement obligation    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [4] 35,270 28,780
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] 35,270  
Long-term service agreement    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 20,955 22,114
Long-term service agreement | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1] 12,679  
Long-term service agreement | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 8,276  
Other regulatory assets (liabilities)    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets 54,903 $ 18,288
Other regulatory assets (liabilities) | Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets [1] 2,330  
Other regulatory assets (liabilities) | Not Earning a Return    
Regulatory Assets and Liabilities [Line Items]    
Regulatory Assets $ 52,573  
[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 2023 were 2% 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] In 2017, income tax reform reduced deferred income tax assets and liabilities. 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 13 - "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]     The energy efficiency asset and liability represent the separate Idaho and Oregon jurisdiction balances at December 31, 2022, and December 31, 2023, respectively. During 2023, the balances changed from an asset to a liability in the Idaho jurisdiction.
[7] This item is discussed in more detail in this Note 3 - "Regulatory Matters."
[8] 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.
[9] Represents flow-through income tax accounting differences which have a corresponding deferred tax liability disclosed in Note 2 - "Income Taxes."
[10] Represents the unfunded obligation of Idaho Power’s pension and postretirement benefit plans, which are discussed in Note 11 - "Benefit Plans."
[11] 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.