Segment Information - Schedule of Product Revenue from Customers by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	$ 7,053	$ 7,230
China
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	6,089	6,113
South Korea
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	502	589
Taiwan
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	192	200
Other
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	$ 270	$ 328