Product warranties (Provision for warranty obligations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jul. 02, 2011	Jun. 30, 2012	Jul. 02, 2011
Product Warranties Disclosures [Abstract]
Balance at beginning of period	$ 32,680	$ 36,437	$ 30,144	$ 37,265
Warranty claims paid during the period	(14,866)	(17,012)	(28,786)	(30,747)
Pre-existing warranty accrual adjustment during the period	0	489	0	3,484
Warranty expense during the period	17,053	12,138	33,509	22,050
Balance at end of period	$ 34,867	$ 32,052	$ 34,867	$ 32,052
Maximum period of product warrants			50 years