Balance Sheet Components (Other long-term liabilities) (Details) - USD ($) $ in Thousands |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Balance Sheet Components | ||
| Deferred revenue | $ 3,087 | $ 3,143 |
| Warranty | 720 | 600 |
| Other | 357 | 199 |
| Total other long-term liabilities | $ 4,164 | $ 3,942 |