OTHER BALANCE SHEET COMPONENTS - Property and equipment, net (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,298		$ 5,376
Less: accumulated depreciation and amortization	(2,878)		(2,648)
Total property and equipment, net	1,420		2,728
Depreciation and amortization expense	230	$ 172
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	274		265
Computer and lab equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,780		3,867
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,244		$ 1,244

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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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