Shareholders' equity - Accumulated other comprehensive income into income expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 25, 2022	Sep. 26, 2021	Sep. 25, 2022	Sep. 26, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	$ 312,833	$ 312,464	$ 924,024	$ 917,779
Total before tax	119,196	229,201	336,503	416,191
(Benefit) tax	(17,315)	(29,695)	(51,700)	(58,535)
Net of tax	101,881	199,506	284,803	357,656
Reclassification out of accumulated other comprehensive income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications, net of tax	(376)	1,597	2,492	5,495
Reclassification out of accumulated other comprehensive income | Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	1,758	2,121	5,747	6,408
Reclassification out of accumulated other comprehensive income | Prior-service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	(252)	(251)	(756)	(753)
Reclassification out of accumulated other comprehensive income | Pension and Other Postretirement Benefits Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	1,506	1,870	4,991	5,655
(Benefit) tax	(352)	(438)	(1,164)	(1,323)
Net of tax	1,154	1,432	3,827	4,332
Reclassification out of accumulated other comprehensive income | Foreign exchange contract | Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	(1,614)	164	(1,445)	1,143
Total before tax	(1,614)	164	(1,445)	1,143
(Benefit) tax	84	1	110	20
Net of tax	$ (1,530)	$ 165	$ (1,335)	$ 1,163