Goodwill and intangible assets - Schedule of intangible assets subject to amortization (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 01, 2016	Oct. 03, 2015	Oct. 01, 2016	Oct. 03, 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			12,502
Intangible assets subject to amortization, ending balance	$ 851,266		851,266
Accumulated amortization, beginning balance			534,572
Amortization during the period	10,381	$ 9,378	29,439	$ 20,748
Currency translation during the period			9,735
Accumulated amortization, ending balance	573,746		573,746
Intangible assets subject to amortization, net	277,520		277,520		$ 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			6,527
Intangible assets subject to amortization, ending balance	595,243		595,243
Accumulated amortization, beginning balance			317,593
Amortization during the period			19,975
Currency translation during the period			3,990
Accumulated amortization, ending balance	341,558		341,558
Intangible assets subject to amortization, net	253,685		253,685
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			6,779
Intangible assets subject to amortization, ending balance	250,037		250,037
Accumulated amortization, beginning balance			216,273
Amortization during the period			9,446
Currency translation during the period			6,103
Accumulated amortization, ending balance	231,822		231,822
Intangible assets subject to amortization, net	18,215		18,215
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			(804)
Intangible assets subject to amortization, ending balance	5,986		5,986
Accumulated amortization, beginning balance			706
Amortization during the period			18
Currency translation during the period			(358)
Accumulated amortization, ending balance	366		366
Intangible assets subject to amortization, net	$ 5,620		$ 5,620