LEASES - Operating lease schedule of maturity (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Leases [Abstract]
2020 (remaining nine months)	$ 835
2021	1,377
2022	1,662
2023	1,712
2024	1,763
2025 and thereafter	4,959
Total lease payments	12,308
Less: imputed interest	(2,578)
Total operating lease liabilities	9,730
Future minimum payments of operating lease	$ 8,200
Term of operating lease not yet commenced, second expansion premises	7 years