SHARE-BASED COMPENSATION - Restricted Stock Unit Activity (Details) - RSUs - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Share-Based Compensation Awards
Stock-based compensation expenses	$ 23	$ 16
Restricted stock units issued and outstanding
Outstanding and expected to vest at beginning of period (in shares)	10,296
Granted (in shares)	17,862
Vested (in shares)	(3,429)
Outstanding and expected to vest at end of period (in shares)	24,729
Weighted average fair value of units granted in period (in dollars per share)	$ 20.74
Unrecognized compensation	$ 486	$ 222
Expected vesting period	2 years 6 months 15 days	2 years 9 months 18 days
Research and development expense
Share-Based Compensation Awards
Stock-based compensation expenses	$ 21	$ 14
General and administrative expense
Share-Based Compensation Awards
Stock-based compensation expenses	$ 2	$ 2

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

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