Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 01, 2017	Apr. 02, 2016	Dec. 31, 2016
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	$ 810,332
Intangible assets recognized or adjusted during the period	827
Currency translation during the period	8,142
Intangible assets subject to amortization, ending balance	819,301
Accumulated amortization, beginning balance	555,873
Amortization during the period	10,059	$ 9,564
Currency translation during the period	5,605
Accumulated amortization, ending balance	571,537
Intangible assets subject to amortization, net	247,764		$ 254,459
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	569,980
Intangible assets recognized or adjusted during the period	827
Currency translation during the period	5,049
Intangible assets subject to amortization, ending balance	575,856
Accumulated amortization, beginning balance	334,276
Amortization during the period	6,397
Currency translation during the period	2,762
Accumulated amortization, ending balance	343,435
Intangible assets subject to amortization, net	232,421
Patents
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	234,022
Intangible assets recognized or adjusted during the period	0
Currency translation during the period	3,020
Intangible assets subject to amortization, ending balance	237,042
Accumulated amortization, beginning balance	220,598
Amortization during the period	3,652
Currency translation during the period	2,841
Accumulated amortization, ending balance	227,091
Intangible assets subject to amortization, net	9,951
Other
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	6,330
Intangible assets recognized or adjusted during the period	0
Currency translation during the period	73
Intangible assets subject to amortization, ending balance	6,403
Accumulated amortization, beginning balance	999
Amortization during the period	10
Currency translation during the period	2
Accumulated amortization, ending balance	1,011
Intangible assets subject to amortization, net	$ 5,392