Revenue From Contracts With Customers - Summary of Product and Service Revenue Disaggregated by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Product and service revenue	$ 6,072	$ 6,955	$ 15,579	$ 18,895
United States
Disaggregation Of Revenue [Line Items]
Product and service revenue	3,119	2,986	7,559	7,644
South Korea
Disaggregation Of Revenue [Line Items]
Product and service revenue	642	2,018	2,048	5,840
Europe
Disaggregation Of Revenue [Line Items]
Product and service revenue	761	697	2,301	2,422
Asia (Excluding South Korea)
Disaggregation Of Revenue [Line Items]
Product and service revenue	1,463	1,181	3,447	2,729
Other
Disaggregation Of Revenue [Line Items]
Product and service revenue	$ 87	$ 73	$ 224	$ 260