Goodwill and intangible assets (Schedule of intangible assets subject to amortization) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2013	Jun. 30, 2012	Jun. 29, 2013	Jun. 30, 2012
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 98,296
Intangible assets acquired during the period			36,980
Amortization during the period	(6,774)	(15,998)	(12,748)	(32,259)
Currency translation during the period			(2,106)
Intangible assets subject to amortization, ending balance	120,422		120,422
Customer Relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			26,210
Intangible assets acquired during the period			21,792
Amortization during the period			(3,147)
Currency translation during the period			(310)
Intangible assets subject to amortization, ending balance	44,545		44,545
Patents [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			71,031
Intangible assets acquired during the period			15,188
Amortization during the period			(9,541)
Currency translation during the period			(1,548)
Intangible assets subject to amortization, ending balance	75,130		75,130
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			1,055
Intangible assets acquired during the period			0
Amortization during the period			(60)
Currency translation during the period			(248)
Intangible assets subject to amortization, ending balance	$ 747		$ 747