Commitments and Contingencies Warranty Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jul. 01, 2017	Jul. 02, 2016
Warranty Liabilities [Roll Forward]
Balance at beginning of year	$ 8,633	$ 10,028
Additions charged to costs and expenses for current-year sales	4,243	6,601
Deductions from reserves	(3,665)	(7,290)
Changes in liability for pre-existing warranties during the current year, including expirations	(55)	(1,515)
Balance at end of period	$ 9,156	$ 7,824