Goodwill and intangible assets (Schedule of intangible assets subject to amortization) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2015	Jun. 28, 2014	Jul. 04, 2015	Jun. 28, 2014	Dec. 31, 2014
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 626,713
Intangible assets acquired during the period			224,326
Currency translation during the period			(42,543)
Intangible assets subject to amortization, ending balance	$ 808,496		808,496
Accumulated amortization, beginning balance			547,395
Amortization during the period	6,264	$ 6,509	11,370	$ 12,547
Currency translation during the period			(36,669)
Accumulated amortization, ending balance	522,096		522,096
Intangible assets subject to amortization, net	286,400		286,400		$ 79,318
Customer Relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			354,768
Intangible assets acquired during the period			223,825
Currency translation during the period			(19,364)
Intangible assets subject to amortization, ending balance	559,229		559,229
Accumulated amortization, beginning balance			320,851
Amortization during the period			4,473
Currency translation during the period			(17,301)
Accumulated amortization, ending balance	308,023		308,023
Intangible assets subject to amortization, net	251,206		251,206
Patents [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			270,466
Intangible assets acquired during the period			0
Currency translation during the period			(23,179)
Intangible assets subject to amortization, ending balance	247,287		247,287
Accumulated amortization, beginning balance			225,875
Amortization during the period			6,892
Currency translation during the period			(19,383)
Accumulated amortization, ending balance	213,384		213,384
Intangible assets subject to amortization, net	33,903		33,903
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			1,479
Intangible assets acquired during the period			501
Currency translation during the period			0
Intangible assets subject to amortization, ending balance	1,980		1,980
Accumulated amortization, beginning balance			669
Amortization during the period			5
Currency translation during the period			15
Accumulated amortization, ending balance	689		689
Intangible assets subject to amortization, net	$ 1,291		$ 1,291