| Share-based Compensation - Share-Based Compensation Expense and Related Tax Benefits (Detail) - USD ($) $ in Thousands | 12 Months Ended | ||
|---|---|---|---|
| Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | |
| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | |||
| Share-based compensation expense | $ 2,544 | $ 3,125 | $ 3,515 | 
| Related tax benefits | $ 734 | $ 941 | $ 984 | 
| X | ||||||||||
| 
- References No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of tax benefit for recognition of expense of award under share-based payment arrangement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount of noncash expense for share-based payment arrangement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 |