SHARE-BASED COMPENSATION - Restricted Stock Unit Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Share-Based Compensation Awards
Stock-based compensation expenses	$ 4,657	$ 1,381
RSUs
Share-Based Compensation Awards
Stock-based compensation expenses	$ 76	$ 0
Restricted stock units issued and outstanding
Granted (in shares)	10,296
Outstanding and expected to vest at end of period (in shares)	10,296
Weighted average fair value of units granted in period (in dollars per share)	$ 23.11
Unrecognized compensation	$ 163
Expected vesting period	2 years 18 days
RSUs \| Research and development expense
Share-Based Compensation Awards
Stock-based compensation expenses	$ 69
RSUs \| General and administrative expense
Share-Based Compensation Awards
Stock-based compensation expenses	$ 7

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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