Stock-Based Compensation - Summary of Stock-Based Compensation Expense Included in Company's Condensed Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Lien Items] | ||||
| Total stock-based compensation expense | $ 2,659 | $ 1,513 | $ 8,102 | $ 2,940 |
| Research and Development Expense [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Lien Items] | ||||
| Total stock-based compensation expense | 871 | 413 | 2,530 | 704 |
| General and Administrative Expense [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Lien Items] | ||||
| Total stock-based compensation expense | $ 1,788 | $ 1,100 | $ 5,572 | $ 2,236 |