Employee Benefit Plans - Schedule of Net Periodic Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Components of Net Periodic Benefits Cost:
Regulatory adjustment - deferred cost	$ (35,863)	$ (5,713)
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	846	1,480
Interest cost	2,513	1,844
Expected return on plan assets	(2,623)	(3,292)
Amortization of prior service cost	108	109
Amortization of actuarial (gain) loss	0	0
Net periodic benefits costs under accounting standards	844	141
Regulatory adjustment - deferred cost	(92)	0
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	752	141
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	33	33
Interest cost	25	16
Expected return on plan assets	(120)	(147)
Amortization of prior service cost	0	0
Amortization of actuarial (gain) loss	(240)	(412)
Net periodic benefits costs under accounting standards	(302)	(510)
Regulatory adjustment - deferred cost	0	0
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	(302)	(510)
SERP
Components of Net Periodic Benefits Cost:
Service cost	312	298
Interest cost	411	256
Expected return on plan assets	0	0
Amortization of prior service cost	0	0
Amortization of actuarial (gain) loss	(8)	145
Net periodic benefits costs under accounting standards	715	699
Regulatory adjustment - deferred cost	0	0
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	$ 715	$ 699