Pension and Other Postretirement Benefit Costs - Net Periodic Benefit Cost - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,049	$ 1,530
Interest cost	5,218	3,659
Expected return on plan assets	(6,661)	(6,427)
Amortization of net actuarial loss	0	0
Defined Benefit Plan, Amortization of Gain (Loss)	139	3,198
Net periodic benefit cost	(255)	1,960
Amount allocated to construction	(474)	(664)
Defined Benefit Plan Net Periodic Benefit Cost Charged To Expense	(729)	1,296
Amortization of Regulatory Balancing Account	2,801	2,801
Net amount charged to expense	2,072	4,097
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	28	47
Interest cost	248	180
Expected return on plan assets	0	0
Amortization of net actuarial loss	0	(83)
Defined Benefit Plan, Amortization of Gain (Loss)	0	99
Net periodic benefit cost	276	243
Amount allocated to construction	(11)	(18)
Defined Benefit Plan Net Periodic Benefit Cost Charged To Expense	265	225
Amortization of Regulatory Balancing Account	0	0
Net amount charged to expense	$ 265	$ 225