Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 02, 2016	Apr. 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	23,611
Intangible assets subject to amortization, ending balance	862,375
Accumulated amortization, beginning balance	534,572
Amortization during the period	9,564	$ 5,106
Currency translation during the period	16,366
Accumulated amortization, ending balance	560,502
Intangible assets subject to amortization, net	301,873		$ 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	13,825
Intangible assets subject to amortization, ending balance	602,541
Accumulated amortization, beginning balance	317,593
Amortization during the period	6,744
Currency translation during the period	7,225
Accumulated amortization, ending balance	331,562
Intangible assets subject to amortization, net	270,979
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	10,217
Intangible assets subject to amortization, ending balance	253,475
Accumulated amortization, beginning balance	216,273
Amortization during the period	2,810
Currency translation during the period	9,165
Accumulated amortization, ending balance	228,248
Intangible assets subject to amortization, net	25,227
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	(431)
Intangible assets subject to amortization, ending balance	6,359
Accumulated amortization, beginning balance	706
Amortization during the period	10
Currency translation during the period	(24)
Accumulated amortization, ending balance	692
Intangible assets subject to amortization, net	$ 5,667