Segment Information and Foreign Operations - Segment and Geographical Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of operating segments | segment	1
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	$ 95,361	$ 83,256	$ 102,397
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	118,508	100,341
China
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	117,672	99,272
North America (primarily the United States)
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	836	1,069
Reportable Geographical Components
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	95,361	83,256	102,397
Reportable Geographical Components | China
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	35,150	26,796	31,492
Reportable Geographical Components | Taiwan
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	16,485	16,204	20,078
Reportable Geographical Components | Japan
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	7,624	6,258	10,305
Reportable Geographical Components | Asia Pacific (excluding China, Taiwan, and Japan)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	5,458	7,592	8,488
Reportable Geographical Components | Europe (primarily Germany)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	19,673	18,178	22,013
Reportable Geographical Components | North America (primarily the United States)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	$ 10,971	$ 8,228	$ 10,021