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Stock-Based Compensation - Additional Information (Detail) - shares | 9 Months Ended
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Sep. 30, 2019 | Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Deferred board fees percentage for stock units accumulation | 100.00% |
Nonqualified Incentive Stock Option Plan [Member] |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Vesting period in years | 7 years |
Nonqualified Incentive Stock Option Plan [Member] | Stock Option [Member] |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Number of shares to be issued under incentive stock option plan | 6,484,530 |
Shares for future grants | 330,000 |
Stock option plan termination date | Dec. 31, 2024 |
Option exercisable rate | 25.00% |
Option exercisable period | 4 years |
Options expire period | 15 years |
Share based compensation options exercisable period | 2026 |
Vesting period in years, start | 4 years |
Options vest and exercisable Description | The options vest and are exercisable beginning four years from the date of grant at the rate of 25% per year for four years. Options expire at the end of fifteen years from the date of grant |
Nonqualified Incentive Stock Option Plan [Member] | Stock Option [Member] | Minimum [Member] |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Stock price percentage to fair value at grant date | 100.00% |
Non-Employee Directors Stock Option Plan [Member] |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Number of shares to be issued under incentive stock option plan | 530,000 |
Shares for future grants | 15,000 |
Stock option plan termination date | Dec. 31, 2024 |
Option exercisable rate | 25.00% |
Option exercisable period | 1 year |
Options expire period | 15 years |
Share based compensation options exercisable period | 2023 |
Options vest and exercisable Description | The options vest and are exercisable beginning one year from the date of grant at the rate of 25% per year for four years |
Number of options granted for non-employee director | 10,000 |
Vesting period in years | 4 years |
Non-Employee Directors Stock Option Plan [Member] | Minimum [Member] |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Stock price percentage to fair value at grant date | 100.00% |
Banc First Deferred Stock Compensation Plan [Member] |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Stock option plan termination date | Dec. 31, 2024 |
Number of shares authorized for issuance under deferred compensation plan | 244,148 |
Number of shares of common stock distributed | 9,542 | 3,891

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