Postretirement Benefits - Reconciliation of Benefit Obligation and Plan Assets, Pension Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Changes in PBO:
PBO at beginning of year	$ 562,567
Service cost	21,568	$ 34,624	$ 31,672
Interest cost	31,367	24,445	21,957
PBO at end of year	627,560	562,567
Pension Plan
Changes in PBO:
PBO at beginning of year	562,567	778,934
Service cost	21,568	34,624
Interest cost	31,367	24,445
Actuarial loss (gain)	40,569	(241,995)
Benefits paid	(28,511)	(33,441)
PBO at end of year	627,560	562,567	778,934
Changes in plan assets:
Fair value at beginning of year	499,775	597,547
Return on assets	75,062	(94,175)
Contributions	24,441	29,844
Benefits paid	(28,511)	(33,441)
Fair value at end of year	570,767	499,775	$ 597,547
Funded status at year end	$ (56,793)	$ (62,792)