Share-Based Compensation - Additional Information (Detail) - USD ($) |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
|
| Disclosure of Compensation Related Costs, Share-based Payments [Abstract] | ||||
| Compensation expense in stock compensation plans | $ 317,526 | $ 411,450 | $ 1,400,000 | $ 1,600,000 |
| Income tax benefit of stock compensation plans | 66,680 | 144,008 | 285,578 | 564,075 |
| Unrecognized compensation expense related to nonvested share-based compensation granted under the plan | 1,400,000 | $ 1,400,000 | ||
| Weighted average period of unrecognized compensation expense | 1 year 4 months 24 days | |||
| Cash from option exercises | 217,112 | 765,127 | $ 695,762.0 | 2,900,000 |
| Tax benefit for tax deductions related to option exercises | $ 2,516 | $ 42,411 | $ 21,319 | $ 220,767 |