Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018	Dec. 31, 2018
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 912,030
Intangible assets recognized during the period			2,092
Currency translation during the period			(31,529)
Intangible assets subject to amortization, ending balance	$ 882,593		882,593
Accumulated amortization, beginning balance			657,601
Amortization during the period	6,912	$ 8,148	20,596	$ 23,198
Currency translation during the period			(22,769)
Accumulated amortization, ending balance	655,428		655,428
Intangible assets subject to amortization, net	227,165		227,165		$ 254,430
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			651,012
Intangible assets recognized during the period			2,092
Currency translation during the period			(20,143)
Intangible assets subject to amortization, ending balance	632,961		632,961
Accumulated amortization, beginning balance			406,386
Amortization during the period			19,027
Currency translation during the period			(11,722)
Accumulated amortization, ending balance	413,691		413,691
Intangible assets subject to amortization, net	219,270		219,270
Patents
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			254,483
Intangible assets recognized during the period			0
Currency translation during the period			(11,213)
Intangible assets subject to amortization, ending balance	243,270		243,270
Accumulated amortization, beginning balance			249,988
Amortization during the period			1,606
Currency translation during the period			(11,028)
Accumulated amortization, ending balance	240,566		240,566
Intangible assets subject to amortization, net	2,704		2,704
Other
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			6,535
Intangible assets recognized during the period			0
Currency translation during the period			(173)
Intangible assets subject to amortization, ending balance	6,362		6,362
Accumulated amortization, beginning balance			1,227
Amortization during the period			(37)
Currency translation during the period			(19)
Accumulated amortization, ending balance	1,171		1,171
Intangible assets subject to amortization, net	$ 5,191		$ 5,191