Pension and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Defined Benefit Plan Deferred Pension And Other Postretirement Benefit Plan Costs Recovered [Abstract]
Deferred (recognized) pension and OPEB costs	$ 400	$ (300)	$ 800	$ (600)
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	694	1,195	1,446	2,532
Interest cost	4,337	2,784	8,659	5,580
Expected return on assets	(6,302)	(7,844)	(12,624)	(15,695)
Amortization of:
Prior service credit	0	(5)	0	(10)
Actuarial (gain) loss	492	484	880	1,208
Net periodic benefit (credit) cost	(779)	(3,386)	(1,639)	(6,385)
Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	190	314	390	647
Interest cost	835	479	1,654	970
Expected return on assets	(646)	(839)	(1,297)	(1,682)
Amortization of:
Transition obligation	0	0	1	1
Prior service credit	0	(75)	0	(149)
Actuarial (gain) loss	(65)	24	(95)	72
Net periodic benefit (credit) cost	$ 314	$ (97)	$ 653	$ (141)