BALANCE SHEET COMPONENTS - Additional information (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Total Property and equipment, cost	$ 13,034	$ 6,643
Less: Accumulated depreciation and amortization	(4,498)	(3,960)
Property and equipment, net	8,536	2,683
Lab equipment
Total Property and equipment, cost	4,530	4,160
Leasehold improvements
Total Property and equipment, cost	2,372	1,776
Computer equipment
Total Property and equipment, cost	258	337
Office furniture and equipment
Total Property and equipment, cost	457	263
Construction in progress
Total Property and equipment, cost	$ 5,417	$ 107