v3.26.1
BENEFIT PLANS: Level 3 (Tables)
 3 Months Ended
Mar. 31, 2026
Retirement Benefits [Abstract]  
Schedule of Defined Benefit Plans Disclosures [Table Text Block] The table below shows the components of net periodic benefit costs for the pension, SMSP, and postretirement benefits plans for the three months ended March 31, 2026 and 2025 (in thousands of dollars).
Pension PlanSMSPPostretirement
Benefits		Total
 20262025202620252026202520262025
Service cost$8,307 $7,857 $240 $293 $188 $169 $8,735 $8,319 
Interest cost14,560 13,867 1,430 1,410 744 743 16,734 16,020 
Expected return on plan assets(18,549)(17,235)— — (455)(450)(19,004)(17,685)
Amortization of prior service cost2 2 56 55 275 344 333 401 
Amortization of net loss— — 240 173 (418)(440)(178)(267)
Net periodic benefit cost4,320 4,491 1,966 1,931 334 366 6,620 6,788 
Regulatory deferral of net periodic benefit cost(1)
(4,129)(4,297)— — — — (4,129)(4,297)
Previously deferred pension costs recognized(1)
8,796 8,796 — — — — 8,796 8,796 
Net periodic benefit cost recognized for financial reporting(1)(2)
$8,987 $8,990 $1,966 $1,931 $334 $366 $11,287 $11,287 
(1) Net periodic benefit costs for the pension plan are recognized for financial reporting based upon the authorization of each regulatory jurisdiction in which Idaho Power operates. Under IPUC order, the Idaho portion of net periodic benefit cost is recorded as a regulatory asset and is recognized in the income statement as those costs are recovered through rates.
(2) Of total net periodic benefit cost recognized for financial reporting, $9.7 million and $9.8 million, respectively, were recognized in "Other operations and maintenance" and $1.6 million and $1.5 million, respectively, were recognized in "Other income, net" on the condensed consolidated statements of income of the companies for the three months ended March 31, 2026 and 2025.