COMMITMENTS AND CONTINGENCIES - Leases expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating lease, weighted average remaining lease term	2 years 6 months		2 years 6 months
Operating lease costs	$ 40	$ 57	$ 132	$ 166
Variable lease costs	9	15	30	44
Total lease costs	$ 49	$ 72	$ 162	$ 210
Minimum
Operating lease liability discount rates (in percent)	3.99%		3.99%
Maximum
Operating lease liability discount rates (in percent)	8.95%		8.95%