Shareholders' equity - Accumulated other comprehensive income into income expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 27, 2022	Mar. 28, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	$ 295,482	$ 289,398
Income from continuing operations before taxes	93,340	87,295
(Benefit) tax	(15,973)	(12,428)
Income from continuing operations	77,367	74,867
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications, net of tax	1,740	2,288
Reclassification out of Accumulated Other Comprehensive Income | Pension and Other Postretirement Benefits Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from continuing operations before taxes	1,748	1,892
(Benefit) tax	(408)	(442)
Income from continuing operations	1,340	1,450
Reclassification out of Accumulated Other Comprehensive Income | Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from continuing operations before taxes	2,000	2,143
Reclassification out of Accumulated Other Comprehensive Income | Prior-service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from continuing operations before taxes	(252)	(251)
Reclassification out of Accumulated Other Comprehensive Income | Foreign exchange contract | Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	398	846
Income from continuing operations before taxes	398	846
(Benefit) tax	2	(8)
Income from continuing operations	$ 400	$ 838