Employee benefits - Funded Status of the plan (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Funded status of the plan:
Fair value of plan assets at end of year	$ 619,885	$ 860,484
Pension Plans
Funded status of the plan:
Benefit obligation at end of year	(628,175)	(851,471)	$ (914,353)
Fair value of plan assets at end of year	619,885	860,484	878,785
Funded status at year end	(8,290)	9,013	(35,568)
OPEB Plan
Funded status of the plan:
Benefit obligation at end of year	(118,336)	(159,958)	(179,210)
Fair value of plan assets at end of year	0	0	0
Funded status at year end	$ (118,336)	$ (159,958)	$ (179,210)