Postretirement Benefits - Reconciliation of Benefit Obligation and Plan Assets, Pension Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Changes in PBO:
PBO at beginning of year	$ 778,934
Service cost	34,624	$ 31,672	$ 24,461
Interest cost	24,445	21,957	22,825
PBO at end of year	562,567	778,934
Pension Plan
Changes in PBO:
PBO at beginning of year	778,934	763,313
Service cost	34,624	31,672
Interest cost	24,445	21,957
Plan amendments	0	4,565
Actuarial loss (gain)	(241,995)	(16,938)
Benefits paid	(33,441)	(25,635)
PBO at end of year	562,567	778,934	763,313
Changes in plan assets:
Fair value at beginning of year	597,547	529,532
Return on assets	(94,175)	75,792
Contributions	29,844	17,858
Benefits paid	(33,441)	(25,635)
Fair value at end of year	499,775	597,547	$ 529,532
Funded status at year end	$ (62,792)	$ (181,387)