BENEFIT PLANS: Defined Benefit Plan, Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure
Net periodic benefit cost	[1]	$ 6,513	$ 9,196	$ 15,249
Pension Plan
Defined Benefit Plan Disclosure
Service cost		29,843	52,025	54,202
Interest cost		51,277	39,670	37,317
Expected return on plan assets		61,728	72,348	64,090
Amortization of net loss		0	(12,273)	(23,796)
Amortization of prior service cost		6	6	6
Net periodic benefit cost		19,398	31,626	51,231
Regulatory deferral of net periodic benfit cost	[2]	18,553	30,197	48,962
Previously deferred pension cost recognized	[2]	17,154	17,154	17,154
Net periodic benefit cost recognized for financial reporting	[2],[3]	17,999	18,583	19,423
Pension and SMSP
Defined Benefit Plan Disclosure
NetServiceCostDefinedBenefitPlan		18,200	19,000	17,800
otherexpensedefinedbenefitplanbenefitcost		6,500	9,200	10,500
Senior Management Security Plan
Defined Benefit Plan Disclosure
Service cost		612	1,185	813
Interest cost		5,322	3,897	3,557
Expected return on plan assets		0	0	0
Amortization of net loss		(570)	(4,229)	(4,205)
Amortization of prior service cost		219	279	296
Net periodic benefit cost		6,723	9,590	8,871
Regulatory deferral of net periodic benfit cost		0	0	0
Net periodic benefit cost recognized for financial reporting	[3]	6,723	9,590	8,871
Postretirement Benefits
Defined Benefit Plan Disclosure
Service cost		658	1,071	1,063
Interest cost		2,980	2,112	2,059
Expected return on plan assets		1,650	2,351	2,395
Amortization of net loss		1,237	31	0
Amortization of prior service cost		1,665	295	47
Net periodic benefit cost		2,416	1,096	$ 5,510
Defined Benefit Plan, Accumulated Benefit Obligation, Increase (Decrease) for Plan Amendment		$ 0	$ 8,065

[1] The 2021 pension and postretirement non-service costs includes $4.7 million of expense for a temporary deviation from the cost-sharing provisions of the substantive postretirement plan as described in Note 11 - "Benefit Plans."

[2] Net periodic pension costs for the pension plan are recognized for financial reporting based upon the authorization of each regulatory jurisdiction in which Idaho Power operates. Under an IPUC order, the Idaho portion of net periodic pension cost is recorded as a regulatory asset and is recognized in the income statement as those costs are recovered through rates.

[3] Of total net periodic pension cost recognized for financial reporting $18.2 million, $19.0 million, and $17.8 million respectively, was recognized in "Other operations and maintenance" and $6.5 million, $9.2 million, and $10.5 million respectively, was recognized in "Other (income) expense, net" on the consolidated statements of income of the companies for the twelve months ended December 31, 2023, 2022, and 2021.