REVENUE - Disaggregation by Country (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]
Revenue	$ 2,646	$ 686	$ 5,376	$ 4,760
China
Disaggregation of Revenue [Line Items]
Revenue	2,051	552	3,383	4,319
United States
Disaggregation of Revenue [Line Items]
Revenue	590	134	1,852	441
Other countries
Disaggregation of Revenue [Line Items]
Revenue	$ 5	$ 0	$ 141	$ 0

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details