Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Parenthetical) (Detail) - shares |
3 Months Ended | 6 Months Ended |
|---|---|---|
Jun. 30, 2017 |
Jun. 30, 2018 |
|
| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | ||
| Stock options granted | 0 | 1,772,037 |
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Gross number of share options (or share units) granted during the period. No definition available.
|