Selected Quarterly Financial Data (Unaudited) - Selected Quarterly Financial Data (Parenthetical) (Detail) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|
Dec. 31, 2018 |
Sep. 30, 2018 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Quarterly Financial Information [Line Items] | ||||
| Stock-based compensation expense | $ 7,121 | $ 1,860 | ||
| Performance-Based (RSUs) [Member] | ||||
| Quarterly Financial Information [Line Items] | ||||
| Stock-based compensation expense | $ 1,100 | $ 600 | $ 1,700 | |
| Out of period adjustments for stock-based compensation expense | $ 800 | |||