Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jul. 02, 2016	Jul. 01, 2017	Jul. 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			3,175
Currency translation during the period			52,263
Intangible assets subject to amortization, ending balance	$ 865,770		865,770
Accumulated amortization, beginning balance			555,873
Amortization during the period	9,322	$ 9,494	19,381	$ 19,058
Currency translation during the period			37,214
Accumulated amortization, ending balance	612,468		612,468
Intangible assets subject to amortization, net	253,302		253,302		$ 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			3,175
Currency translation during the period			31,814
Intangible assets subject to amortization, ending balance	604,969		604,969
Accumulated amortization, beginning balance			334,276
Amortization during the period			12,945
Currency translation during the period			17,851
Accumulated amortization, ending balance	365,072		365,072
Intangible assets subject to amortization, net	239,897		239,897
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			20,158
Intangible assets subject to amortization, ending balance	254,180		254,180
Accumulated amortization, beginning balance			220,598
Amortization during the period			6,404
Currency translation during the period			19,362
Accumulated amortization, ending balance	246,364		246,364
Intangible assets subject to amortization, net	7,816		7,816
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			291
Intangible assets subject to amortization, ending balance	6,621		6,621
Accumulated amortization, beginning balance			999
Amortization during the period			32
Currency translation during the period			1
Accumulated amortization, ending balance	1,032		1,032
Intangible assets subject to amortization, net	$ 5,589		$ 5,589