Postretirement Benefits - Funding Policy/Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Postretirement benefits
Employer contributions during fiscal year	$ 96,222	$ 25,764
Net amount recognized in the Statements of Financial Position:
Funded status at end of year	3,325	(53,948)
Pension asset	34,320	0
Pension liabilities – due within one year	(4,735)	(2,724)
Pension liabilities – due after one year	(26,260)	(51,224)
Net amount recognized	$ 3,325	(53,948)
Employee Pension Plan
Postretirement benefits
Funding target (as a percentage of the funding target liability)	100.00%
Employer contributions during fiscal year	$ 95,000	$ 25,000
Employer contributions, 2024	33,000
Net amount recognized in the Statements of Financial Position:
Pension asset	$ 34,300