Shareholders' equity - Accumulated other comprehensive income into income expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2019	Sep. 30, 2018	Sep. 29, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	$ 272,639	$ 267,099	$ 821,064	$ 788,147
Total before tax	(98,546)	(55,254)	(238,608)	(123,451)
Taxes on income from continuing operations	130,383	1,286	115,567	(14,532)
Net of tax	(228,929)	(56,540)	(354,175)	(108,919)
Interest expense	19,545	27,171	62,995	79,763
Total reclassifications, net of tax	(3,002)	1,214	(7,331)	3,111
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications, net of tax			(748)	(873)
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	1,716	1,640	5,194	5,120
Prior-service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	21	24	65	71
Pension and Other Postretirement Benefits Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	1,737	1,664	5,259	5,191
Tax benefit	(405)	(388)	(1,226)	(1,207)
Total reclassifications, net of tax	1,332	1,276	4,033	3,984
Reclassification out of Accumulated Other Comprehensive Income | Foreign exchange contract | Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	(523)	(87)	(888)	(1,038)
Total before tax	(523)	(87)	(888)	(1,038)
Taxes on income from continuing operations	(46)	(25)	(140)	(165)
Net of tax	(477)	(62)	(748)	(873)
Reclassification out of Accumulated Other Comprehensive Income | Cross-currency interest rate swap | Net Investment Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	5,021	0	13,820	0
Taxes on income from continuing operations	1,164	0	3,204	0
Net of tax	(3,857)	0	(10,616)	0
Interest expense	$ (5,021)	$ 0	$ (13,820)	$ 0