Product warranties (Provision for warranty obligations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at beginning of period	$ 32,930	$ 30,144
Warranty claims paid during the period	(13,301)	(13,920)
Warranty expense during the period	15,854	16,456
Balance at end of period	$ 35,483	$ 32,680
Product warranty period, maximum	50 years