Income Taxes - Tax credit carry forwards (Details) - USD ($) $ in Millions |
Dec. 31, 2016 |
Apr. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|---|
| Tax Credit Carryforward [Line Items] | |||
| Common stock, shares issued | 20,922,428 | 1,431,615 | |
| Research and development credits | Federal | |||
| Tax Credit Carryforward [Line Items] | |||
| Research and development tax credit carryforwards | $ 1.3 | ||
| Research and development credits | State | |||
| Tax Credit Carryforward [Line Items] | |||
| Research and development tax credit carryforwards | $ 1.7 | ||
| IPO | |||
| Tax Credit Carryforward [Line Items] | |||
| Common stock, shares issued | 5,200,000 |