Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 4,652	$ 3,180
Accumulated depreciation and amortization	(298)	(166)
Property and equipment, net	4,354	3,014
Construction-in-progress [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	309	2,259
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	2,171	3
Furniture & Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	99	99
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	48	40
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 2,025	$ 779

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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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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