Employee benefits - Funded Status of the plan (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Funded status of the plan:
Fair value of plan assets at end of year	$ 617,175	$ 652,426
Pension Plans
Funded status of the plan:
Benefit obligation at end of year	(589,758)	(635,794)	$ (628,175)
Fair value of plan assets at end of year	617,175	652,426	619,885
Funded status at year end	27,417	16,632	(8,290)
OPEB Plan
Funded status of the plan:
Benefit obligation at end of year	(99,172)	(117,045)	(118,336)
Fair value of plan assets at end of year	0	0	0
Funded status at year end	$ (99,172)	$ (117,045)	$ (118,336)