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Intangible Assets and Goodwill - Additional Information (Detail) - USD ($) |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Aug. 15, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Weighted-average life |  | 7 years 7 months 6 days |  |
Goodwill |  | $ 148,604,000 | $ 79,749,000 | $ 54,042,000
Pegasus Bank [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Date of acquisition | Aug. 15, 2019 |  |  |
Goodwill | $ 68,900,000 | $ 68,855,000 |  |
Customer Related Intangibles [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Weighted-average life |  | 4 years 9 months 18 days |  |
Customer Related Intangibles [Member] | BancFirst Insurance Services, Inc. [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Impairment of intangible assets |  | $ 353,000 |  |
Core Deposit Intangibles [Member] |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Weighted-average life |  | 7 years 9 months 18 days |  |

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