Warranties (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 27, 2014	Sep. 28, 2013	Sep. 27, 2014	Sep. 28, 2013
Components of the warranty accrual
Balance at beginning of the period	$ 3,484	$ 3,519	$ 3,426	$ 4,203
Accruals for warranties	1,242	1,161	4,459	2,886
Settlements during the period	(1,736)	(1,278)	(4,895)	(3,687)
Balance at end of the period	$ 2,990	$ 3,402	$ 2,990	$ 3,402