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Employee Benefit Plans - Schedule of Net Periodic Costs (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Pension Benefits    
Components of Net Periodic Benefits Cost:    
Service cost $ 774 $ 850
Interest cost 2,706 2,550
Expected return on plan assets (3,183) (3,009)
Amortization of prior service cost 108 108
Amortization of actuarial (gain) loss 0 0
Net periodic benefits costs under accounting standards 405 499
Total expense (benefit) recognized, before surcharges and allocation to overhead pool 405 499
Other Postretirement Benefits    
Components of Net Periodic Benefits Cost:    
Service cost 27 32
Interest cost 24 23
Expected return on plan assets (161) (142)
Amortization of prior service cost 0 0
Amortization of actuarial (gain) loss (291) (263)
Net periodic benefits costs under accounting standards (401) (350)
Total expense (benefit) recognized, before surcharges and allocation to overhead pool (401) (350)
SERP    
Components of Net Periodic Benefits Cost:    
Service cost 181 358
Interest cost 485 426
Expected return on plan assets 0 0
Amortization of prior service cost 0 0
Amortization of actuarial (gain) loss 0 (4)
Net periodic benefits costs under accounting standards 666 780
Total expense (benefit) recognized, before surcharges and allocation to overhead pool $ 666 $ 780