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Junior Subordinated Debentures - Additional Information (Detail) - USD ($) |  | 1 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Oct. 08, 2015 | Mar. 31, 2004 | Feb. 29, 2004 | Dec. 31, 2019 | Dec. 31, 2018
Junior Subordinated Debentures [Line Items] |  |  |  |  |
Junior subordinated notes assumed |  |  |  | $ 26,804,000 | $ 26,804,000
BancFirst Capital Trust Two [Member] | Subordinated Debentures Subject to Mandatory Redemption [Member] |  |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |  |
Interest rate of securities |  |  |  | 7.20% |
Frequency of payment |  |  |  | payable January 15, April 15, July 15 and October 15 of each year. |
Junior subordinated notes assumed |  |  |  | $ 26,800,000 |
Debt instrument maturity date |  |  |  | Mar. 31, 2034 |
BancFirst Capital Trust Two [Member] | Cumulative Preferred Stock [Member] |  |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |  |
Issue of securities |  | $ 1,000,000 | $ 25,000,000 |  |
Cumulative trust preferred securities interest rate |  |  |  | 7.20% |
CSB Bancshares Statutory Trust I [Member] |  |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |  |
Business combination, acquisition of capital securities | $ 5,000,000.0 |  |  |  |
Business combination, acquisition of common securities | 155,000 |  |  |  |
CSB Bancshares Statutory Trust I [Member] | Subordinated Deferrable Interest Debentures [Member] |  |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |  |
Frequency of payment |  |  |  | payable March 15, June 15, September 15 and December 15 of each year |
Junior subordinated notes assumed | $ 5,200,000 |  |  |  |
Debt instrument maturity date | Sep. 15, 2036 |  |  |  |
CSB Bancshares Statutory Trust I [Member] | Subordinated Deferrable Interest Debentures [Member] | LIBOR [Member] |  |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |  |
Debt instrument, Basis point rate | 1.82% |  |  |  |

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