Equity-Based Compensation - Schedule of Equity-based Compensation Expense (Detail) - USD ($) $ in Thousands |
3 Months Ended | |
---|---|---|
Mar. 31, 2019 |
Mar. 31, 2018 |
|
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
Stock-based compensation expense | $ 3,500 | $ 819 |
Research and Development [Member] | ||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
Stock-based compensation expense | 1,819 | 632 |
Selling, General and Administrative [Member] | ||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
Stock-based compensation expense | $ 1,681 | $ 187 |