COMMITMENTS AND CONTINGENCIES - Leases expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating lease, weighted average remaining lease term	2 years 8 months 12 days		2 years 8 months 12 days
Operating lease costs	$ 43	$ 57	$ 92	$ 109
Variable lease costs	13	14	21	29
Total lease costs	$ 56	$ 71	$ 113	$ 138
Minimum
Operating lease liability discount rates (in percent)	3.99%		3.99%
Maximum
Operating lease liability discount rates (in percent)	8.95%		8.95%