Employee Benefit Plans - Schedule of Net Periodic Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Components of Net Periodic Benefits Cost:
Regulatory adjustments - deferred			$ (86,070)	$ (14,065)
Pension Benefits
Components of Net Periodic Benefits Cost:
Service cost	$ 705	$ 1,411	2,397	4,233
Interest cost	2,581	1,850	7,607	5,550
Expected return on plan assets	(2,617)	(3,291)	(7,863)	(9,873)
Amortization of prior service cost	110	109	326	327
Amortization of actuarial (gain) loss	0	0	0	0
Net periodic benefits costs under accounting standards	779	79	2,467	237
Regulatory adjustments - deferred	(27)	0	(211)	0
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	752	79	2,256	237
Other Postretirement Benefits
Components of Net Periodic Benefits Cost:
Service cost	33	30	99	96
Interest cost	26	13	77	45
Expected return on plan assets	(119)	(147)	(358)	(441)
Amortization of prior service cost	0	0	0	0
Amortization of actuarial (gain) loss	(242)	(478)	(724)	(1,302)
Net periodic benefits costs under accounting standards	(302)	(582)	(906)	(1,602)
Regulatory adjustments - deferred	0	0	0	0
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	(302)	(582)	(906)	(1,602)
SERP
Components of Net Periodic Benefits Cost:
Service cost	312	298	936	894
Interest cost	411	256	1,233	768
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Amortization of actuarial (gain) loss	(8)	145	(24)	435
Net periodic benefits costs under accounting standards	715	699	2,145	2,097
Regulatory adjustments - deferred	0	0	0	0
Total expense (benefit) recognized, before surcharges and allocation to overhead pool	$ 715	$ 699	$ 2,145	$ 2,097