Income Taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Summary of unrecognized tax benefits | ||
| Unrecognized tax benefits beginning of the period | $ 135 | |
| Increase related to the prior year | 6 | |
| Increased related to the current year | 463 | $ 135 |
| Unrecognized tax benefits, end of the period | $ 604 | $ 135 |