Revenue Recognition Sales Returns (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017
Sales Return Liability [Roll Forward]
Balance at beginning of year	$ 19,270	$ 15,222
Additions that reduce net sales	36,555	32,434
Deductions from reserves	(39,298)	(35,054)
Balance at end of period	$ 16,527	$ 12,602