Goodwill and intangible assets (Schedule of intangible assets subject to amortization) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 29, 2014	Mar. 30, 2013	Dec. 31, 2013
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	$ 692,046
Currency translation during the period	(1,755)
Intangible assets subject to amortization, ending balance	690,291
Accumulated amortization, beginning balance	581,036
Amortization during the period	6,038	5,974
Currency translation during the period	(1,463)
Accumulated amortization, ending balance	585,611
Intangible assets subject to amortization, net	104,680		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	(646)
Intangible assets subject to amortization, ending balance	382,713
Accumulated amortization, beginning balance	342,361
Amortization during the period	1,606
Currency translation during the period	(624)
Accumulated amortization, ending balance	343,343
Intangible assets subject to amortization, net	39,370
Patents [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	307,186
Currency translation during the period	(1,112)
Intangible assets subject to amortization, ending balance	306,074
Accumulated amortization, beginning balance	238,115
Amortization during the period	4,401
Currency translation during the period	(840)
Accumulated amortization, ending balance	241,676
Intangible assets subject to amortization, net	64,398
Other [Member]
Finite-lived Intangible Assets [Roll Forward]
Intangible assets subject to amortization, beginning balance	1,501
Currency translation during the period	3
Intangible assets subject to amortization, ending balance	1,504
Accumulated amortization, beginning balance	560
Amortization during the period	31
Currency translation during the period	1
Accumulated amortization, ending balance	592
Intangible assets subject to amortization, net	$ 912