Loans and Allowance for Credit Losses - PCD Loans (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Line Items]
Non-credit related discount	$ (7,700)	$ (26,400)
Spirit of Texas Bancshares, Inc.
Financing Receivable, Allowance for Credit Loss [Line Items]
Unpaid principal balance	74,851
PCD allowance for credit loss at acquisition	(9,622)
Non-credit related discount	(1,377)
Fair value of PCD loans	63,852
Spirit of Texas Bancshares, Inc. \| Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Unpaid principal balance	8,258
PCD allowance for credit loss at acquisition	(6,433)
Non-credit related discount	(378)
Fair value of PCD loans	1,447
Spirit of Texas Bancshares, Inc. \| Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Unpaid principal balance	66,534
PCD allowance for credit loss at acquisition	(3,187)
Non-credit related discount	(998)
Fair value of PCD loans	62,349
Spirit of Texas Bancshares, Inc. \| Credit cards
Financing Receivable, Allowance for Credit Loss [Line Items]
Unpaid principal balance	0
PCD allowance for credit loss at acquisition	0
Non-credit related discount	0
Fair value of PCD loans	0
Spirit of Texas Bancshares, Inc. \| Other Consumer and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Unpaid principal balance	59
PCD allowance for credit loss at acquisition	(2)
Non-credit related discount	(1)
Fair value of PCD loans	$ 56

Financing Receivable, Purchased With Credit Deterioration, Unpaid Principal Balance

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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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

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- Definition

Amount of allowance for credit loss at acquisition date of financing receivable purchased with credit deterioration.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 19
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-19

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- Definition

Amount at purchase price of financing receivable purchased with credit deterioration.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 19
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-19

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- Definition

Amount of discount (premium) attributable to other factors on financing receivable purchased with credit deterioration.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 19
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-19

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