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Stockholders' Equity - Additional Information (Detail) - USD ($) | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Jan. 01, 2018 | Dec. 31, 2016 | Dec. 31, 2015
Stockholders Equity [Line Items] |  |  |  |
Increase remaining shares to be purchased | 300,000 |  | 300,000 | 332,552
2016 [Member] |  |  |  |
Stockholders Equity [Line Items] |  |  |  |
Implementation of the capital conservation buffer, Percentage | 0.625% |  |  |
Capital conservation buffer implementation phase-in period | 4 years |  |  |
2019 [Member] |  |  |  |
Stockholders Equity [Line Items] |  |  |  |
Capital Conservation Buffer Maximum Level | 2.50% |  |  |
Maximum [Member] |  |  |  |
Stockholders Equity [Line Items] |  |  |  |
Quantitative limit for trust preferred securities to be included in tier 1 capital | $ 15,000,000,000 |  |  |
Subsequent Event [Member] |  |  |  |
Stockholders Equity [Line Items] |  |  |  |
Available equity of BancFirst for dividend payments to the company |  | $ 100,800,000 |  |
Senior Preferred Stock [Member] |  |  |  |
Stockholders Equity [Line Items] |  |  |  |
Preferred stock, shares issued | 0 |  | 0 |
Preferred stock, shares outstanding | 0 |  |  |
Cumulative Preferred Stock [Member] |  |  |  |
Stockholders Equity [Line Items] |  |  |  |
Preferred stock, shares issued | 0 |  | 0 |
Preferred stock, shares outstanding | 0 |  |  |
Dividend payable at redemption, per share | $ 5.00 |  |  |
Cumulative preferred stock dividend rate | 10.00% |  |  |

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