Segment Information and Foreign Operations - Segment and Geographical Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)	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	$ 19,841	$ 28,626	$ 64,846	$ 80,165
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	92,661		92,661		$ 82,280
Reportable Geographical Components | China
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	5,117	10,268	21,870	26,271
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	91,487		91,487		81,835
Reportable Geographical Components | Europe (primarily Germany)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	4,737	4,879	13,752	17,957
Reportable Geographical Components | Taiwan
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	4,399	6,116	12,062	15,445
Reportable Geographical Components | Asia Pacific (excluding China, Taiwan, and Japan)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	2,234	2,334	6,156	6,399
Reportable Geographical Components | North America (primarily the United States)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	2,015	2,967	6,365	7,052
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	1,174		1,174		$ 445
Reportable Geographical Components | Japan
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	$ 1,339	$ 2,062	$ 4,641	$ 7,041