Income Taxes - Summary of Changes in Valuation Allowance (Detail) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Income Tax Disclosure [Abstract] | ||
| Valuation allowance as of beginning of year | $ 5,677 | $ 3,795 |
| Increases recorded to accumulated deficit (adoption of ASU 2016-09) | 876 | |
| Decreases recorded as a benefit to income tax provision | (1,368) | |
| Increases recorded to tax provision | 5,580 | 2,374 |
| Valuation allowance as of end of year | $ 11,257 | $ 5,677 |