REVENUE - Disaggregation by Country (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 4,016	$ 2,299	$ 8,422	$ 2,730
China
Disaggregation of Revenue [Line Items]
Revenue	1,418	987	5,135	1,311
United States
Disaggregation of Revenue [Line Items]
Revenue	$ 2,598	$ 1,312	$ 3,287	$ 1,419

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