Pension and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Defined Benefit Plan Deferred Pension And Other Postretirement Benefit Plan Costs Recovered [Abstract]
Deferred (recognized) pension and OPEB costs	$ (300)	$ (200)	$ (600)	$ (3,600)
Deferred savings from current year employee benefit plan costs	800	2,600	800	2,600
Returned savings from prior year employee benefit costs	1,100		2,100
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	1,195	1,442	2,532	2,864
Interest cost	2,784	2,288	5,580	4,560
Expected return on assets	(7,844)	(7,368)	(15,695)	(14,743)
Amortization of:
Prior service credit	(5)	(31)	(10)	(62)
Actuarial loss	484	1,743	1,208	3,323
Net periodic benefit (credit) cost	(3,386)	(1,926)	(6,385)	(4,058)
Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	314	373	647	724
Interest cost	479	390	970	774
Expected return on assets	(839)	(821)	(1,682)	(1,638)
Amortization of:
Transition obligation	0	1	1	1
Prior service credit	(75)	(380)	(149)	(759)
Actuarial loss	24	138	72	247
Net periodic benefit (credit) cost	$ (97)	$ (299)	$ (141)	$ (651)