Earnings Per Common Share - Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Share (Parenthetical) (Detail) - shares |
3 Months Ended | 9 Months Ended | |
|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2017 |
Sep. 30, 2018 |
|
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
| Shares subject to stock options, outstanding | 0 | ||
| Employee Stock Option [Member] | |||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||
| Antidilutive securities excluded from computation of earnings per common share | 39,000 | 39,000 |