Fair Value Measurements - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Days from origination after which mortgage loans are sold	30 days
Amount of non-financial assets (liabilities) measured at fair value on a recurring basis	$ 0	$ 0
Non-financial assets or liabilities for which no impairment was provided	0	0
Level 2 Inputs [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Loans held for sale	$ 20,950,000	53,719,000
Level 2 Inputs [Member] \| BancFirst [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Loans held for sale		$ 21,600,000

Non financial assets liabilities for which no impairment provided.

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- Definition

Amount of non-financial assets (liabilities) measured at fair value on a recurring basis.

+ References

No definition available.

+ Details

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- Definition

Period for sale of mortgage loan from origination.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount, before valuation allowance, of financing receivable classified as held-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=120238483&loc=d3e48678-111004

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