Retirement plans - Schedule of Pension Costs (Details) - Retirement Plans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Service cost-benefits earned during the period	$ 0	$ 0	$ 2
Interest cost on benefit obligation	24,183	16,830	15,887
Expected return on plan assets	(20,940)	(19,502)	(34,679)
Amortization of prior service cost	90	90	90
Amortization of actuarial loss	6,059	4,583	4,952
Pension payment timing related charge	0	300	946
Expense for (income from) company-sponsored retirement plans	$ 9,392	$ 2,301	$ (12,802)