Warranties (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Components of the warranty accrual [Roll Forward]
Balance as of beginning of period	$ 4,602	$ 4,556	$ 3,838	$ 4,504
Accruals for warranties issued during period	1,020	1,100	3,800	3,529
Settlements during the period	(1,080)	(1,471)	(3,096)	(3,848)
Balance as of end of period	$ 4,542	$ 4,185	$ 4,542	$ 4,185