Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 459	$ 429
Less: accumulated depreciation	(334)	(275)
Total property and equipment, net	125	154
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	259	254
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	89	93
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	108	79
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3	$ 3

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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