Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||
| Stock-based compensation expense | $ 1,370 | $ 413 |
| Research and Development | ||
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||
| Stock-based compensation expense | 974 | 170 |
| General and Administrative | ||
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||
| Stock-based compensation expense | $ 396 | $ 243 |