Product Warranty Reserves (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Product Warranties Disclosures [Abstract]
Product warranty reserve at beginning of period	$ 1,944	$ 2,168	$ 2,307	$ 2,159
Warranty liabilities accrued	1,590	1,685	2,913	3,037
Warranty liabilities settled	(1,503)	(1,785)	(2,971)	(3,545)
Changes for pre-existing warranty liabilities	114	146	(104)	563
Product warranty reserve at end of period	$ 2,145	$ 2,214	$ 2,145	$ 2,214