Composition of Certain Financial Statement Items - Property and Equipment (Details) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended |
|---|---|---|
Mar. 31, 2018 |
Dec. 31, 2017 |
|
| Property and Equipment | ||
| Property and equipment, gross | $ 1,794 | $ 1,804 |
| Less: accumulated depreciation | (883) | (810) |
| Property and equipment, net | 911 | 994 |
| Depreciation and amortization expenses | 90 | 43 |
| Computer equipment and software | ||
| Property and Equipment | ||
| Property and equipment, gross | 333 | 351 |
| Furniture and office equipment | ||
| Property and Equipment | ||
| Property and equipment, gross | 137 | 137 |
| Manufacturing equipment | ||
| Property and Equipment | ||
| Property and equipment, gross | 1,108 | 1,108 |
| Research and development equipment | ||
| Property and Equipment | ||
| Property and equipment, gross | 30 | 30 |
| Leasehold improvements | ||
| Property and Equipment | ||
| Property and equipment, gross | $ 186 | $ 178 |