Segment Information - Schedule of Net Long-Lived Assets by Geographic Region (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment - net	$ 452	$ 325
Taiwan
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment - net	288	205
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment - net	81	92
Japan
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment - net	73	16
China
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment - net	5	9
South Korea
Revenues From External Customers And Long Lived Assets [Line Items]
Property and equipment - net	$ 5	$ 3