Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 40,129	$ 40,552
Less: accumulated depreciation	(14,595)	(11,395)
Property and equipment, net	25,534	29,157
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	27,282	26,961
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	8,881	8,281
Computer and Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,312	2,292
Furniture
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,586	1,560
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 68	$ 1,458

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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