Disaggregation of Sales, Geographic Sales and Product Sales - Net Sales by Geographic Areas (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Geographic And Sales [Line Items]
Total net sales		$ 39,664	$ 33,905	$ 72,247	$ 60,998
Geographic Distribution, Domestic [Member]
Geographic And Sales [Line Items]
Total net sales		2,114	1,895	4,066	3,651
Geographic Distribution, Foreign [Member]
Geographic And Sales [Line Items]
Total net sales		37,550	32,010	68,181	57,347
China [Member]
Geographic And Sales [Line Items]
Total net sales		19,394	13,965	31,165	21,875
JAPAN
Geographic And Sales [Line Items]
Total net sales		6,275	6,692	11,794	11,775
Other [Member]
Geographic And Sales [Line Items]
Total net sales	[1]	$ 13,995	$ 13,248	$ 29,288	$ 27,348

[1] No other location individually exceeds 10% of the total sales.