Pension Plans and Other Postretirement Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Settlement loss			$ 11,800
Pension Plan And SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	[1]	$ 14,350	23,877	$ 25,306
Interest cost		33,245	26,536	26,160
Expected return on plan assets		$ (43,656)	$ (43,872)	$ (39,088)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax
Amortization of prior service cost		$ 491	$ 257	$ 257
Net loss recognition		4,915	4,180	6,645
Settlement loss	[2]		11,828
Net periodic benefit cost		9,345	22,806	19,280
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	[1]	2,394	4,369	4,114
Interest cost		6,766	5,503	5,139
Expected return on plan assets		$ (3,562)	$ (2,799)	$ (2,400)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax
Amortization of prior service cost		$ (1,050)	$ (1,050)	$ (921)
Net loss recognition		319	3,344	3,865
Net periodic benefit cost		$ 4,867	$ 9,367	$ 9,797

[1] Total service costs in the table above are recorded to the same accounts as labor expense. Labor and benefits expense is recorded to various projects based on whether the work is a capital project or an operating expense. Approximately 40 percent of all labor and benefits is capitalized to utility property and 60 percent is expensed to utility other operating expenses.

[2] The settlement loss was deferred as a regulatory asset and is being amortized over 12 years in accordance with regulatory accounting orders.