Retirement plans - Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Comprehensive Income (Loss) [Line Items]
Current year net actuarial (loss)/gain	$ 1,108	$ 2,387	$ (21,892)
Amortization of previously deferred prior service costs	6,031	5,590	4,158
Pension and other postretirement benefit items	17,455	7,977	(17,434)
Retirement Plans
Comprehensive Income (Loss) [Line Items]
Current year net actuarial (loss)/gain	(2,392)	2,356	(23,688)
Amortization of actuarial loss	5,942	6,059	4,583
Amortization of previously deferred prior service costs	90	90	90
Pension settlement charge	10,316	0	300
Pension and other postretirement benefit items	$ 13,956	$ 8,505	$ (18,715)