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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, 2017 | Dec. 31, 2016
Junior Subordinated Debentures [Line Items] |  |  |  |  |
Junior subordinated notes assumed |  |  |  | $ 31,959,000 | $ 31,959,000
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 |  |  |  |
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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- Definition Cumulative trust preferred securities interest rate. + References No definition available. + Details
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- Definition Junior subordinated debentures. + References No definition available. + Details
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- Definition Description of the frequency of periodic payments (monthly, quarterly, annual). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Including the current and noncurrent portions, carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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