Stock Plan and Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
|
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Stock-based compensation expense | $ 2,276 | $ 1,751 | $ 4,618 | $ 3,547 |
| Research and Development [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Stock-based compensation expense | 986 | 655 | 2,098 | 1,304 |
| General and Administrative [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Stock-based compensation expense | $ 1,290 | $ 1,096 | $ 2,520 | $ 2,243 |