Product warranties (Provision for warranty obligations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 29, 2012	Oct. 01, 2011	Sep. 29, 2012	Oct. 01, 2011
Product Warranties Disclosures [Abstract]
Balance at beginning of period	$ 34,867	$ 32,052	$ 30,144	$ 37,265
Warranty claims paid during the period	(15,166)	(13,247)	(43,952)	(43,994)
Pre-existing warranty accrual adjustment during the period	0	300	0	3,784
Warranty expense during the period	14,748	10,140	48,257	32,190
Balance at end of period	$ 34,449	$ 29,245	$ 34,449	$ 29,245
Product warranty period, maximum			50 years