Segment Information and Foreign Operations - Segment and Geographical Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)	Dec. 31, 2017 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	$ 27,120	$ 23,557	$ 51,539	$ 44,173
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	65,174		65,174		$ 46,530
Reportable Geographical Components | China
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	8,820	6,324	16,003	10,746
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	64,321		64,321		45,120
Reportable Geographical Components | Europe (primarily Germany)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	6,685	5,848	13,078	11,446
Reportable Geographical Components | Taiwan
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	4,280	4,195	9,329	7,513
Reportable Geographical Components | Asia Pacific (excluding China, Taiwan, and Japan)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	2,571	2,645	4,065	4,716
Reportable Geographical Components | Japan
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	2,524	2,862	4,979	6,002
Reportable Geographical Components | North America (primarily the United States)
Net revenues reported for products shipped to customers in corresponding geographic region [Abstract]
Revenue	2,240	$ 1,683	4,085	$ 3,750
Long-lived assets by geographic region, net of depreciation:
Long-lived assets	$ 853		$ 853		$ 1,410