Retirement Plans, Summary of Funded Status at End of Year (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Plan [Member]
Funded status at end of year [Abstract]
Fair value of plan assets	$ 375,917	$ 341,061	$ 430,821
Benefit obligations	(342,749)	(339,509)	(495,272)
Funded status and amount recognized at end of year	33,168	1,552
SERP [Member]
Funded status at end of year [Abstract]
Fair value of plan assets	0	0	0
Benefit obligations	(814)	(833)	(1,033)
Funded status and amount recognized at end of year	(814)	(833)
Other Postretirement Benefits [Member]
Funded status at end of year [Abstract]
Fair value of plan assets	0	0	0
Benefit obligations	(415)	(432)	$ (582)
Funded status and amount recognized at end of year	$ (415)	$ (432)