Pension Plans and Other Postretirement Benefit Plans - Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities		$ (14,082)	$ (15,625)
Non-current liabilities		(89,830)	(93,901)
Accumulated other comprehensive loss for unfunded benefit obligation for pensions and other postretirement benefit plans		(357)	(2,058)
Pension Plan And SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year		557,709	799,042
Service cost	[1]	14,350	23,877	$ 25,306
Interest cost		$ 33,245	$ 26,536	26,160
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]		Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses	Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses
Actuarial (gain)/loss		$ 21,373	$ (204,775)
Plan change			3,302
Settlement			(60,206)
Benefits paid		(41,432)	(30,067)
Benefit obligation as of end of year		585,245	557,709	799,042
Fair value of plan assets as of beginning of year		540,703	750,963
Actual return on plan assets		78,838	(163,866)
Employer contributions		10,000	42,000
Settlement			(60,206)
Benefits paid		(39,558)	(28,188)
Fair value of plan assets as of end of year		589,983	540,703	750,963
Funded status		4,738	(17,006)
Other non-current assets		32,997	13,382
Other current liabilities		(2,212)	(1,934)
Non-current liabilities		(26,047)	(28,454)
Net amount recognized		4,738	(17,006)
Accumulated pension benefit obligation		514,295	495,654
Unrecognized prior service cost (credit)		3,717	4,105
Unrecognized net actuarial loss		69,002	83,794
Total		72,719	87,899
Less regulatory asset		(71,983)	(85,198)
Accumulated other comprehensive loss for unfunded benefit obligation for pensions and other postretirement benefit plans		$ 736	$ 2,701
Discount rate for benefit obligation		5.86%	6.10%
Discount rate for annual expense		6.10%	3.39%
Expected long-term return on plan assets		8.30%	5.80%
Rate of compensation increase		4.87%	4.69%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year		$ 115,635	$ 167,598
Service cost	[1]	2,394	4,369	4,114
Interest cost		$ 6,766	$ 5,503	5,139
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]		Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses	Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses
Actuarial (gain)/loss		$ 4,799	$ (54,120)
Benefits paid		(7,210)	(7,715)
Benefit obligation as of end of year		122,384	115,635	167,598
Fair value of plan assets as of beginning of year		49,472	59,544
Actual return on plan assets		8,654	(10,072)
Fair value of plan assets as of end of year		58,126	49,472	$ 59,544
Funded status		(64,258)	(66,163)
Other current liabilities		(652)	(706)
Non-current liabilities		(63,606)	(65,457)
Net amount recognized		(64,258)	(66,163)
Unrecognized prior service cost (credit)		(1,081)	(1,911)
Unrecognized net actuarial loss		13,103	13,643
Total		12,022	11,732
Less regulatory asset		(12,401)	(12,375)
Accumulated other comprehensive loss for unfunded benefit obligation for pensions and other postretirement benefit plans		$ (379)	$ (643)
Discount rate for benefit obligation		5.83%	6.10%
Discount rate for annual expense		6.10%	3.40%
Expected long-term return on plan assets		7.20%	4.70%
Other Postretirement Benefits [Member] | Pre-Age 65 [Member]
Defined Benefit Plan Disclosure [Line Items]
Medical cost trend – initial		6.50%	6.25%
Medical cost trend – ultimate		5.00%	5.00%
Ultimate medical cost trend year		2030	2028
Other Postretirement Benefits [Member] | Post-Age 65 [Member]
Defined Benefit Plan Disclosure [Line Items]
Medical cost trend – initial		6.50%	6.25%
Medical cost trend – ultimate		5.00%	5.00%
Ultimate medical cost trend year		2030	2028
Other Postretirement Benefits [Member] | Retirees [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year		$ 61,984
Benefit obligation as of end of year		68,087	$ 61,984
Other Postretirement Benefits [Member] | Fully eligible employees [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year		19,731
Benefit obligation as of end of year		16,054	19,731
Other Postretirement Benefits [Member] | Other participants [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation as of beginning of year		33,920
Benefit obligation as of end of year		$ 38,243	$ 33,920

[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.