Goodwill and intangible assets (Schedule of intangible assets subject to amortization) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 28, 2013	Sep. 29, 2012	Sep. 28, 2013	Sep. 29, 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	(13,288)	(15,683)	(19,262)	(47,942)
Currency translation during the period			510
Intangible assets subject to amortization, ending balance	116,524		116,524
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			(4,712)
Currency translation during the period			(412)
Intangible assets subject to amortization, ending balance	42,878		42,878
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			(14,418)
Currency translation during the period			1,117
Intangible assets subject to amortization, ending balance	72,918		72,918
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			(132)
Currency translation during the period			(195)
Intangible assets subject to amortization, ending balance	$ 728		$ 728