Accumulated other comprehensive loss - Reclassifications out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	$ 1,498	$ 1,388	$ 4,493	$ 4,165
Income tax effect	(386)	(356)	(1,160)	(1,067)
Total reclassifications, net of tax	1,112	1,032	3,333	3,098
Amortization of prior service cost (credit), net
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	23	(116)	68	(348)
Amortization of actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	$ 1,475	$ 1,504	$ 4,425	$ 4,513