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. 27, 2014	Sep. 28, 2013	Sep. 27, 2014	Sep. 28, 2013	Dec. 31, 2013
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			$ 692,046
Currency translation during the period			(43,788)
Intangible assets subject to amortization, ending balance	648,258		648,258
Accumulated amortization, beginning balance			581,036
Amortization during the period	6,140	13,288	18,687	19,262
Currency translation during the period			(39,009)
Accumulated amortization, ending balance	560,714		560,714
Intangible assets subject to amortization, net	87,544		87,544		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			(18,825)
Intangible assets subject to amortization, ending balance	364,534		364,534
Accumulated amortization, beginning balance			342,361
Amortization during the period			5,225
Currency translation during the period			(18,811)
Accumulated amortization, ending balance	328,775		328,775
Intangible assets subject to amortization, net	35,759		35,759
Patents [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			307,186
Currency translation during the period			(24,957)
Intangible assets subject to amortization, ending balance	282,229		282,229
Accumulated amortization, beginning balance			238,115
Amortization during the period			13,369
Currency translation during the period			(20,194)
Accumulated amortization, ending balance	231,290		231,290
Intangible assets subject to amortization, net	50,939		50,939
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance			1,501
Currency translation during the period			(6)
Intangible assets subject to amortization, ending balance	1,495		1,495
Accumulated amortization, beginning balance			560
Amortization during the period			93
Currency translation during the period			(4)
Accumulated amortization, ending balance	649		649
Intangible assets subject to amortization, net	$ 846		$ 846