v3.26.1
Pension and Other Postretirement Benefit Costs - Schedule of Net Benefit Costs (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Pension Benefits        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service cost $ 854 $ 886 $ 1,709 $ 1,771
Interest cost 5,166 5,410 10,333 10,820
Expected return on plan assets (5,590) (5,433) (11,181) (10,866)
Amortization of net actuarial loss 2,296 2,445 4,591 4,889
Net periodic benefit cost 2,726 3,308 5,452 6,614
Amount allocated to construction (417) (429) (822) (863)
Net periodic benefit cost charged to expense 2,309 2,879 4,630 5,751
Amortization of regulatory balancing account 1,281 1,281 4,082 4,082
Net amount charged to expense 3,590 4,160 8,712 9,833
Other Postretirement Benefits        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service cost 27 28 53 55
Interest cost 282 289 564 577
Expected return on plan assets 0 0 0 0
Amortization of net actuarial loss 62 21 125 41
Net periodic benefit cost 371 338 742 673
Amount allocated to construction (11) (11) (22) (22)
Net periodic benefit cost charged to expense 360 327 720 651
Amortization of regulatory balancing account 0 0 0 0
Net amount charged to expense $ 360 $ 327 $ 720 $ 651