Postretirement Benefits - Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Projected benefit obligation:
Projected benefit obligation, beginning of year	$ 993,554	$ 883,814
Service cost for benefits earned	34,554	28,763	$ 50,242
Interest cost on benefit obligation	52,688	50,193	39,764
Plan amendments	1,146	583
Actuarial (gain) loss	(28,250)	65,041
Benefits paid	(35,924)	(34,840)
Settlements	(4,001)	0
Projected benefit obligation, end of year	1,013,767	993,554	$ 883,814
Accumulated benefit obligation, end of year	$ 860,855	$ 847,143