Postretirement Benefits - Reconciliation of Benefit Obligation and Plan Assets, Pension Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Changes in PBO:
PBO at beginning of year	$ 763,313
PBO at end of year	778,934	$ 763,313
Pension plan
Changes in PBO:
PBO at beginning of year	763,313	665,207
Service cost	31,672	24,461	$ 19,929
Interest cost	21,957	22,825	23,827
Plan amendments	4,565	0
Actuarial loss (gain)	(16,938)	74,006
Benefits paid	(25,635)	(23,186)
PBO at end of year	778,934	763,313	665,207
Changes in plan assets:
Fair value at beginning of year	529,532	468,763
Return on assets	75,792	62,104
Contributions	17,858	21,851
Benefits paid	(25,635)	(23,186)
Fair value at end of year	597,547	529,532	$ 468,763
Funded status at year end	$ (181,387)	$ (233,781)