Segment Information - Schedule of Product Revenue from Customers by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	$ 9,613	$ 8,667	$ 21,809	$ 22,190
China
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	7,582	6,992	15,768	18,175
Taiwan
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	940	589	2,833	933
South Korea
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	894	705	2,445	2,018
Japan
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	170	370	673	1,047
Other
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	$ 27	$ 11	$ 90	$ 17