Accumulated other comprehensive loss - Reclassifications out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	$ 1,375	$ 1,500
Income tax effect	(352)	(389)
Total reclassifications, net of tax	1,023	1,111
Amortization of prior service (credit) cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	(50)	25
Amortization of actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	$ 1,425	$ 1,475