Product warranties (Provision for warranty obligations) (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
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at beginning of period	$ 33,674	$ 34,867	$ 32,930	$ 30,144
Warranty claims paid during the period	(12,144)	(15,166)	(41,751)	(43,952)
Product Warranty Accrual, Preexisting, Increase (Decrease)	48	0	3,331	0
Warranty expense during the period	11,989	14,748	39,057	48,257
Balance at end of period	$ 33,567	$ 34,449	$ 33,567	$ 34,449
Product warranty period, maximum			50 years