Retirement plans - Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Comprehensive Income (Loss) [Line Items]
Current year net actuarial (loss) gain	$ (21,892)	$ 4,463	$ 22,574
Amortization of previously deferred prior service costs	4,158	5,217	6,209
Pension and other postretirement benefit items	(17,434)	10,626	28,783
Retirement Plans
Comprehensive Income (Loss) [Line Items]
Current year net actuarial (loss) gain	(23,688)	4,463	23,597
Amortization of actuarial loss	4,583	4,952	6,207
Amortization of previously deferred prior service costs	90	90	91
Pension payment timing related charges	300	946	0
Pension and other postretirement benefit items	$ (18,715)	$ 10,451	$ 29,895