Product Warranty Reserves (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 25, 2016	Jun. 27, 2015	Jun. 25, 2016	Jun. 27, 2015
Product Warranties Disclosures [Abstract]
Product warranty reserve at beginning of period	$ 2,168	$ 2,545	$ 2,159	$ 2,214
Warranty liabilities accrued	1,685	1,469	3,037	3,277
Warranty liabilities settled	(1,785)	(2,814)	(3,545)	(4,802)
Changes for pre-existing warranty liabilities	146	915	563	1,426
Product warranty reserve at end of period	$ 2,214	$ 2,115	$ 2,214	$ 2,115