Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 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			(2,990)
Intangible assets subject to amortization, ending balance	$ 910,736		910,736
Accumulated amortization, beginning balance			674,790
Amortization during the period	6,980	$ 6,955	13,856	$ 13,684
Currency translation during the period			476
Accumulated amortization, ending balance	689,122		689,122
Intangible assets subject to amortization, net	221,614		221,614		$ 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			(3,214)
Intangible assets subject to amortization, ending balance	654,781		654,781
Accumulated amortization, beginning balance			426,765
Amortization during the period			12,774
Currency translation during the period			46
Accumulated amortization, ending balance	439,585		439,585
Intangible assets subject to amortization, net	215,196		215,196
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			419
Intangible assets subject to amortization, ending balance	249,519		249,519
Accumulated amortization, beginning balance			246,872
Amortization during the period			1,037
Currency translation during the period			434
Accumulated amortization, ending balance	248,343		248,343
Intangible assets subject to amortization, net	1,176		1,176
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			(195)
Intangible assets subject to amortization, ending balance	6,436		6,436
Accumulated amortization, beginning balance			1,153
Amortization during the period			45
Currency translation during the period			(4)
Accumulated amortization, ending balance	1,194		1,194
Intangible assets subject to amortization, net	$ 5,242		$ 5,242