Balance Sheet Components - Components of Property and Equipment (Detail) - USD ($) $ in Thousands |
Sep. 30, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Property, Plant and Equipment [Line Items] | ||
| Property and equipment, gross | $ 955 | $ 675 |
| Less: Accumulated depreciation and amortization | (593) | (495) |
| Total property and equipment, net | 362 | 180 |
| Computer Equipment [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property and equipment, gross | 30 | 30 |
| Lab Equipment [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property and equipment, gross | 676 | 543 |
| Furniture and Fixtures [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property and equipment, gross | 21 | 21 |
| Machinery and Equipment [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property and equipment, gross | 173 | 26 |
| Leasehold Improvements [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Property and equipment, gross | $ 55 | $ 55 |