v3.24.2.u1
Pension and Other Postretirement Benefit Costs - Net Periodic Benefit Cost - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2024
Jun. 30, 2023
Jun. 30, 2024
Jun. 30, 2023
Pension Benefits        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service cost $ 979 $ 1,049 $ 1,959 $ 2,098
Interest cost 5,159 5,218 10,319 10,436
Expected return on plan assets (5,936) (6,210) (11,871) (12,871)
Defined Benefit Plan, Amortization of Gain (Loss) 1,496 140 2,991 279
Net periodic benefit cost 1,698 197 3,398 (58)
Amount allocated to construction (476) (439) (901) (913)
Defined Benefit Plan Net Periodic Benefit Cost Charged To Expense 1,222 (242) 2,497 (971)
Amortization of Regulatory Balancing Account 1,281 1,281 4,082 4,082
Net amount charged to expense 2,503 1,039 6,579 3,111
Other Postretirement Benefits        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service cost 24 28 49 56
Interest cost 247 248 495 496
Expected return on plan assets 0 0 0 0
Defined Benefit Plan, Amortization of Gain (Loss) 0 0 0 0
Net periodic benefit cost 271 276 544 552
Amount allocated to construction (10) (9) (18) (20)
Defined Benefit Plan Net Periodic Benefit Cost Charged To Expense 261 267 526 532
Amortization of Regulatory Balancing Account 0 0 0 0
Net amount charged to expense $ 261 $ 267 $ 526 $ 532