Commitments and Contingencies Warranty Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jul. 04, 2015	Jun. 28, 2014
Warranty Liabilities [Roll Forward]
Balance at beginning of year	$ 5,824	$ 4,153
Additions charged to costs and expenses for current-year sales	4,869	3,237
Deductions from reserves	(4,177)	(3,231)
Changes in liability for pre-existing warranties during the current year, including expirations	421	274
Balance at end of period	$ 6,937	$ 4,433