Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
|
| Deferred Compensation Arrangement With Individual Share Based Payments [Line Items] | ||||
| Stock-based compensation expense | $ 3,660 | $ 3,661 | $ 10,844 | $ 10,030 |
| Research and Development | ||||
| Deferred Compensation Arrangement With Individual Share Based Payments [Line Items] | ||||
| Stock-based compensation expense | 1,973 | 1,639 | 5,707 | 4,490 |
| General and Administrative | ||||
| Deferred Compensation Arrangement With Individual Share Based Payments [Line Items] | ||||
| Stock-based compensation expense | $ 1,687 | $ 2,022 | $ 5,137 | $ 5,540 |