Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017	Dec. 31, 2017
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 899,057
Intangible assets recognized during the period			43,642
Currency translation during the period			(24,174)
Intangible assets subject to amortization, ending balance	$ 918,525		918,525
Accumulated amortization, beginning balance			651,498
Amortization during the period	8,148	$ 7,421	23,198	$ 26,802
Currency translation during the period			(17,484)
Accumulated amortization, ending balance	657,212		657,212
Intangible assets subject to amortization, net	261,313		261,313		$ 247,559
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			625,263
Intangible assets recognized during the period			43,635
Currency translation during the period			(15,102)
Intangible assets subject to amortization, ending balance	653,796		653,796
Accumulated amortization, beginning balance			390,428
Amortization during the period			21,429
Currency translation during the period			(8,798)
Accumulated amortization, ending balance	403,059		403,059
Intangible assets subject to amortization, net	250,737		250,737
Patents
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			266,969
Intangible assets recognized during the period			0
Currency translation during the period			(8,889)
Intangible assets subject to amortization, ending balance	258,080		258,080
Accumulated amortization, beginning balance			259,908
Amortization during the period			1,713
Currency translation during the period			(8,673)
Accumulated amortization, ending balance	252,948		252,948
Intangible assets subject to amortization, net	5,132		5,132
Other
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			6,825
Intangible assets recognized during the period			7
Currency translation during the period			(183)
Intangible assets subject to amortization, ending balance	6,649		6,649
Accumulated amortization, beginning balance			1,162
Amortization during the period			56
Currency translation during the period			(13)
Accumulated amortization, ending balance	1,205		1,205
Intangible assets subject to amortization, net	$ 5,444		$ 5,444