Share-based Compensation - Additional Information (Detail) - shares |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | ||
| Shares issued under stock purchase plan, stock option exercises and restricted stock | 126,511 | 214,679 |