Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019	Dec. 31, 2019
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 900,937
Intangible assets recognized during the period			12,789
Currency translation during the period			22,143
Intangible assets subject to amortization, ending balance	$ 935,869		935,869
Accumulated amortization, beginning balance			674,790
Amortization during the period	7,327	$ 6,912	21,183	$ 20,596
Currency translation during the period			19,684
Accumulated amortization, ending balance	715,657		715,657
Intangible assets subject to amortization, net	220,212		220,212		$ 226,147
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			645,206
Intangible assets recognized during the period			12,789
Currency translation during the period			12,622
Intangible assets subject to amortization, ending balance	670,617		670,617
Accumulated amortization, beginning balance			426,765
Amortization during the period			19,531
Currency translation during the period			10,173
Accumulated amortization, ending balance	456,469		456,469
Intangible assets subject to amortization, net	214,148		214,148
Patents
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			249,100
Intangible assets recognized during the period			0
Currency translation during the period			9,548
Intangible assets subject to amortization, ending balance	258,648		258,648
Accumulated amortization, beginning balance			246,872
Amortization during the period			1,595
Currency translation during the period			9,495
Accumulated amortization, ending balance	257,962		257,962
Intangible assets subject to amortization, net	686		686
Other
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			6,631
Intangible assets recognized during the period			0
Currency translation during the period			(27)
Intangible assets subject to amortization, ending balance	6,604		6,604
Accumulated amortization, beginning balance			1,153
Amortization during the period			57
Currency translation during the period			16
Accumulated amortization, ending balance	1,226		1,226
Intangible assets subject to amortization, net	$ 5,378		$ 5,378