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. 30, 2012	Jul. 02, 2011	Jun. 30, 2012	Jul. 02, 2011
Finite-Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, beginning balance			$ 154,668
Amortization during the period	(15,998)	(17,975)	(32,259)	(35,374)
Currency translation during the period			(1,997)
Intangible assets subject to amortization, ending balance	120,412		120,412
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, beginning balance			64,958
Amortization during the period			(22,791)
Currency translation during the period			(191)
Intangible assets subject to amortization, ending balance	41,976		41,976
Patents [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, beginning balance			88,544
Amortization during the period			(9,408)
Currency translation during the period			(1,809)
Intangible assets subject to amortization, ending balance	77,327		77,327
Other [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, beginning balance			1,166
Amortization during the period			(60)
Currency translation during the period			3
Intangible assets subject to amortization, ending balance	$ 1,109		$ 1,109