Shareholders' equity - Accumulated other comprehensive income into income expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2020	Sep. 29, 2019	Sep. 27, 2020	Sep. 29, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	$ 298,977	$ 293,244	$ 884,657	$ 883,127
Total before tax	(115,654)	(98,546)	(281,171)	(238,608)
(Benefit) taxes on income from continuing operations	(951)	(130,383)	21,971	(115,567)
Net of tax	(116,605)	(228,929)	(259,200)	(354,175)
Total reclassifications, net of tax	3,073	855	5,201	3,285
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications, net of tax			1,021	(748)
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	1,731	1,716	5,433	5,194
Prior-service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	9	21	25	65
Pension and Other Postretirement Benefits Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	1,740	1,737	5,458	5,259
Tax benefit	(411)	(405)	(1,278)	(1,226)
Total reclassifications, net of tax	1,329	1,332	4,180	4,033
Reclassification out of Accumulated Other Comprehensive Income | Foreign exchange contract | Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	1,899	(523)	1,148	(888)
Total before tax	1,899	(523)	1,148	(888)
(Benefit) taxes on income from continuing operations	(155)	46	(127)	140
Net of tax	$ 1,744	$ (477)	$ 1,021	$ (748)