Employee benefits - Aggregate status of the plans and the amounts recognized in the consolidated financial statements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	$ 860,484
Fair value of plan assets at end of year	619,885	$ 860,484
Pension Plans
Change in benefit obligation:
Benefit obligation at beginning of year	851,471	914,353
Service cost	0	0	$ 0
Interest cost	19,199	15,993	23,389
Actuarial loss (gain)	(194,473)	(34,297)
Benefits paid	(48,022)	(44,578)
Other Adjustments	0	0	0
Benefit obligation at end of year	628,175	851,471	914,353
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	860,484	878,785
Actual return on plan assets	(192,807)	26,049
Employer contribution	230	228
Benefits paid	(48,022)	(44,578)
Fair value of plan assets at end of year	619,885	860,484	878,785
OPEB Plan
Change in benefit obligation:
Benefit obligation at beginning of year	159,958	179,210
Service cost	485	642	713
Interest cost	3,931	3,573	4,913
Actuarial loss (gain)	(39,479)	(17,286)
Benefits paid	(6,619)	(6,181)
Other Adjustments	60	0	0
Benefit obligation at end of year	118,336	159,958	179,210
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contribution	6,619	6,181
Benefits paid	(6,619)	(6,181)
Fair value of plan assets at end of year	$ 0	$ 0	$ 0