Stock Option Plans - Schedule of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] | |||
| Stock-based compensation expense | $ 2,375 | $ 885 | $ 622 |
| Research and Development [Member] | |||
| Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] | |||
| Stock-based compensation expense | 795 | 317 | 284 |
| General and Administrative [Member] | |||
| Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] | |||
| Stock-based compensation expense | $ 1,580 | $ 568 | $ 338 |