Pension and other postretirement benefits - Net benefit cost of pension and postretirement benefit plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,346	$ 1,467	$ 1,416
Interest cost	10,776	9,272	12,827
Expected return on plan assets	(25,776)	(30,726)	(31,650)
Net amortization and deferral	7,900	8,589	7,447
Net benefit (income) expense	(5,754)	(11,398)	(9,960)
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	477	418	902
Expected return on plan assets	0	0	0
Net amortization and deferral	(1,258)	(1,058)	(161)
Net benefit (income) expense	$ (781)	$ (640)	$ 741