Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jul. 04, 2015	Jul. 02, 2016	Jul. 04, 2015	Dec. 31, 2015
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 838,764
Intangible assets recognized or adjusted during the period			0
Currency translation during the period			7,420
Intangible assets subject to amortization, ending balance	$ 846,184		846,184
Accumulated amortization, beginning balance			534,572
Amortization during the period	9,494	$ 6,264	19,058	$ 11,370
Currency translation during the period			5,993
Accumulated amortization, ending balance	559,623		559,623
Intangible assets subject to amortization, net	286,561		286,561		$ 304,192
Customer Relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			588,716
Intangible assets recognized or adjusted during the period			0
Currency translation during the period			3,566
Intangible assets subject to amortization, ending balance	592,282		592,282
Accumulated amortization, beginning balance			317,593
Amortization during the period			13,419
Currency translation during the period			2,126
Accumulated amortization, ending balance	333,138		333,138
Intangible assets subject to amortization, net	259,144		259,144
Patents [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			243,258
Intangible assets recognized or adjusted during the period			0
Currency translation during the period			4,580
Intangible assets subject to amortization, ending balance	247,838		247,838
Accumulated amortization, beginning balance			216,273
Amortization during the period			5,623
Currency translation during the period			4,064
Accumulated amortization, ending balance	225,960		225,960
Intangible assets subject to amortization, net	21,878		21,878
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			6,790
Intangible assets recognized or adjusted during the period			0
Currency translation during the period			(726)
Intangible assets subject to amortization, ending balance	6,064		6,064
Accumulated amortization, beginning balance			706
Amortization during the period			16
Currency translation during the period			(197)
Accumulated amortization, ending balance	525		525
Intangible assets subject to amortization, net	$ 5,539		$ 5,539