Disaggregation of Revenues, Geographic Sales and Product Sales - Revenue from External Customers by Geographic Areas (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 29, 2019	Mar. 30, 2018
Geographic And Sales [Line Items]
Total net sales		$ 32,583	$ 27,093
Geographic Distribution, Domestic [Member]
Geographic And Sales [Line Items]
Total net sales		1,952	1,756
Geographic Distribution, Foreign [Member]
Geographic And Sales [Line Items]
Total net sales		30,631	25,337
China [Member]
Geographic And Sales [Line Items]
Total net sales		11,771	7,910
JAPAN
Geographic And Sales [Line Items]
Total net sales		5,519	5,083
Korea
Geographic And Sales [Line Items]
Total net sales		3,291	2,195
Other [Member]
Geographic And Sales [Line Items]
Total net sales	[1]	$ 12,002	$ 11,905

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