Product warranties (Provision for warranty obligations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2013	Jun. 30, 2012	Jun. 29, 2013	Jun. 30, 2012
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at beginning of period	$ 35,483	$ 32,680	$ 32,930	$ 30,144
Warranty claims paid during the period	(16,306)	(14,866)	(29,607)	(28,786)
Product Warranty Accrual, Preexisting, Increase (Decrease)	503	0	3,283	0
Warranty expense during the period	13,994	17,053	27,068	33,509
Balance at end of period	$ 33,674	$ 34,867	$ 33,674	$ 34,867
Product warranty period, maximum			50 years