OTHER BALANCE SHEET COMPONENTS - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,376	$ 3,136
Less: accumulated depreciation and amortization	(2,648)	(1,921)
Total property and equipment, net	2,728	1,215
Depreciation and amortization expense	757	618	$ 335
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	265	193
Computer and lab equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,867	1,888
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,244	$ 1,055

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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