Employee Benefit Plans - Schedule of Net Periodic Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Components of Net Periodic Benefits Cost:
Regulatory adjustments - deferred	$ (2,234)	$ (35,863)
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	850	846
Interest cost	2,550	2,513
Expected return on plan assets	(3,009)	(2,623)
Amortization of prior service cost	108	108
Amortization of actuarial (gain) loss	0	0
Net periodic benefits costs under accounting standards	499	844
Regulatory adjustments - deferred	0	(92)
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	499	752
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	32	33
Interest cost	23	25
Expected return on plan assets	(142)	(120)
Amortization of prior service cost	0	0
Amortization of actuarial (gain) loss	(263)	(240)
Net periodic benefits costs under accounting standards	(350)	(302)
Regulatory adjustments - deferred	0	0
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	(350)	(302)
SERP
Components of Net Periodic Benefits Cost:
Service cost	358	312
Interest cost	426	411
Expected return on plan assets	0	0
Amortization of prior service cost	0	0
Amortization of actuarial (gain) loss	(4)	(8)
Net periodic benefits costs under accounting standards	780	715
Regulatory adjustments - deferred	0	0
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	$ 780	$ 715