v3.26.3
BENEFIT PLANS: Level 3 (Tables)
 9 Months Ended
Sep. 30, 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 September 30, 2026 and 2025 (in thousands of dollars).
Pension PlanSMSPPostretirement
Benefits		Total
20262025202620252026202520262025
Service cost$8,168 $8,115 $240 $293 $166 $168 $8,574 $8,576 
Interest cost14,539 14,379 1,430 1,410 735 743 16,704 16,532 
Expected return on plan assets(18,539)(17,229)— — (453)(447)(18,992)(17,676)
Amortization of prior service cost2 2 55 55 275 344 332 401 
Amortization of net loss— — 241 173 (422)(441)(181)(268)
Net periodic benefit cost4,170 5,267 1,966 1,931 301 367 6,437 7,565 
Regulatory deferral of net periodic benefit cost(1)
(3,985)(5,058)— — — — (3,985)(5,058)
Previously deferred pension costs recognized(1)
8,796 8,796 — — — — 8,796 8,796 
Net periodic benefit cost recognized for financial reporting(1)(2)
$8,981 $9,005 $1,966 $1,931 $301 $367 $11,248 $11,303 
(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, $9.8 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 September 30, 2026 and 2025.
The table below shows the components of net periodic benefit costs for the pension, SMSP, and postretirement benefits plans for the nine months ended September 30, 2026 and 2025 (in thousands of dollars).
Pension PlanSMSPPostretirement
Benefits		Total
20262025202620252026202520262025
Service cost$24,505 $23,830 $720 $879 $497 $504 $25,722 $25,213 
Interest cost43,617 42,113 4,291 4,230 2,207 2,230 50,115 48,573 
Expected return on plan assets(55,617)(51,698)— — (1,360)(1,340)(56,977)(53,038)
Amortization of prior service cost5 5 166 166 824 1,031 995 1,202 
Amortization of net loss— — 721 518 (1,266)(1,324)(545)(806)
Net periodic benefit cost12,510 14,250 5,898 5,793 902 1,101 19,310 21,144 
Regulatory deferral of net periodic benefit cost(1)
(11,955)(13,620)— — — — (11,955)(13,620)
Previously deferred pension costs recognized(1)
26,387 26,387 — — — — 26,387 26,387 
Net periodic benefit cost recognized for financial reporting(1)(2)
$26,942 $27,017 $5,898 $5,793 $902 $1,101 $33,742 $33,911 
(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, $29.1 million and $29.4 million, respectively, were recognized in "Other operations and maintenance" and $4.6 million and $4.5 million, respectively, were recognized in "Other income, net" on the condensed consolidated statements of income of the companies for the nine months ended September 30, 2026 and 2025.