Employee Benefit Plans - Components of Net Periodic Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Union plan
Weighted-average assumptions used to determine net periodic cost:
Expected long-term return on plan assets	5.75%	5.50%	5.50%
Non-union plan
Weighted-average assumptions used to determine net periodic cost:
Expected long-term return on plan assets	4.00%	3.90%	3.90%
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	$ 3,323	$ 3,196	$ 5,644
Interest cost	10,241	10,142	7,401
Expected return on plan assets	(12,030)	(10,483)	(13,166)
Amortization of prior service cost (credit)	434	434	434
Amortization of actuarial (gain) loss	0	0	0
Net periodic pension cost under accounting standards	1,968	3,289	313
Regulatory adjustment	0	(281)	0
Total expense recognized, before surcharges and allocation to overhead pool	$ 1,968	$ 3,008	$ 313
Weighted-average assumptions used to determine net periodic cost:
Discount rate	5.16%	5.41%	2.89%
Expected long-term return on plan assets	6.00%	5.75%	5.75%
Pension Benefits | Minimum
Weighted-average assumptions used to determine net periodic cost:
Rate of compensation increase	2.50%	2.50%	2.50%
Pension Benefits | Maximum
Weighted-average assumptions used to determine net periodic cost:
Rate of compensation increase	6.00%	6.00%	6.00%
Post-Retirement Medical Benefits
Components of Net Periodic Benefits Cost:
Service cost	$ 128	$ 130	$ 129
Interest cost	98	106	60
Expected return on plan assets	(567)	(477)	(587)
Amortization of prior service cost (credit)	0	0	0
Amortization of actuarial (gain) loss	(1,112)	(969)	(1,734)
Net periodic pension cost under accounting standards	(1,453)	(1,210)	(2,132)
Regulatory adjustment	0	0	0
Total expense recognized, before surcharges and allocation to overhead pool	$ (1,453)	$ (1,210)	$ (2,132)
Weighted-average assumptions used to determine net periodic cost:
Discount rate	5.04%	5.34%	2.46%