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. 28, 2014	Jun. 29, 2013	Jun. 28, 2014	Jun. 29, 2013	Dec. 31, 2013
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 692,046
Currency translation during the period			(5,776)
Intangible assets subject to amortization, ending balance	686,270		686,270
Accumulated amortization, beginning balance			581,036
Amortization during the period	6,509	6,774	12,547	12,748
Currency translation during the period			(5,223)
Accumulated amortization, ending balance	588,360		588,360
Intangible assets subject to amortization, net	97,910		97,910		111,010
Customer Relationships [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			383,359
Currency translation during the period			(2,295)
Intangible assets subject to amortization, ending balance	381,064		381,064
Accumulated amortization, beginning balance			342,361
Amortization during the period			3,528
Currency translation during the period			(2,503)
Accumulated amortization, ending balance	343,386		343,386
Intangible assets subject to amortization, net	37,678		37,678
Patents [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			307,186
Currency translation during the period			(3,494)
Intangible assets subject to amortization, ending balance	303,692		303,692
Accumulated amortization, beginning balance			238,115
Amortization during the period			8,957
Currency translation during the period			(2,726)
Accumulated amortization, ending balance	244,346		244,346
Intangible assets subject to amortization, net	59,346		59,346
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			1,501
Currency translation during the period			13
Intangible assets subject to amortization, ending balance	1,514		1,514
Accumulated amortization, beginning balance			560
Amortization during the period			62
Currency translation during the period			6
Accumulated amortization, ending balance	628		628
Intangible assets subject to amortization, net	$ 886		$ 886