Property and Equipment - Net - Additional Information (Detail) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
|
| Property Plant And Equipment [Abstract] | ||||
| Depreciation expense | $ 2.1 | $ 1.9 | $ 5.4 | $ 5.3 |