Retirement Plans, Components of Net Pension Cost for the Retirement Account Plan Tables (Details) - RAP - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net period benefit cost for the pension and postretirement plans
Service cost	$ 3,189	$ 3,670	$ 7,779
Interest cost	10,887	7,152	6,570
Expected return on plan assets	(32,862)	(26,903)	(25,675)
Amortization of prior service cost	(250)	(250)	(73)
Amortization of actuarial loss	0	658	4,594
Recognized settlement loss	0	0	434
Total net periodic pension (income)	$ (19,037)	$ (15,673)	$ (6,370)