Balance Sheet Details - Summary of Components of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,446	$ 2,016
Less accumulated depreciation and amortization	(1,382)	(967)
Property and equipment, net	2,064	1,049
Research equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,656	1,620
Computer and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	208	97
Office equipment and furniture [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	524	255
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 58	$ 44

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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