Pension Plans and Other Postretirement Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plan And SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	[1]	$ 25,306	$ 22,392	$ 19,755
Interest cost		26,160	27,853	28,417
Expected return on plan assets		(39,088)	(34,886)	(31,763)
Amortization of prior service cost		257	257	257
Net loss recognition		6,645	6,717	10,216
Net periodic benefit cost		19,280	22,333	26,882
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	[1]	4,114	3,902	3,006
Interest cost		5,139	6,042	5,598
Expected return on plan assets		(2,400)	(2,377)	(2,101)
Amortization of prior service cost		(921)	(958)	(981)
Net loss recognition		3,865	4,871	4,013
Net periodic benefit cost		$ 9,797	$ 11,480	$ 9,535

[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.