Pension and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan Deferred Pension And Other Postretirement Benefit Plan Costs Recovered [Abstract]
Deferred (recognized) pension and OPEB costs	$ 1,600	$ (200)	$ 2,400	$ (800)
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	723	1,266	2,169	3,798
Interest cost	4,330	2,791	12,989	8,371
Expected return on assets	(6,312)	(7,848)	(18,936)	(23,543)
Amortization of:
Prior service credit	0	(5)	0	(15)
Actuarial (gain) loss	440	604	1,320	1,812
Net periodic benefit (credit) cost	(819)	(3,192)	(2,458)	(9,577)
Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	195	323	585	970
Interest cost	827	485	2,481	1,455
Expected return on assets	(649)	(842)	(1,946)	(2,524)
Amortization of:
Transition obligation	1	1	2	2
Prior service credit	0	(74)	0	(223)
Actuarial (gain) loss	(48)	37	(143)	109
Net periodic benefit (credit) cost	$ 326	$ (70)	$ 979	$ (211)