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Loans and Allowance for Credit Losses (Details) - Schedule of allowance for credit losses for unfunded loan commitments - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Line Items]
Balance, beginning of period			$ 39,914
Balance, end of period	$ 41,799		41,799
Allowance For Credit Losses Unfunded Loan Commitments [Member]
Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Line Items]
Balance, beginning of period	1,506	$ 1,406	1,456	$ 1,831
Provision for (reversal of) credit losses	350		400	(425)
Balance, end of period	1,856	1,406	1,856	1,406
Unfunded Loan Commitments	$ 836,396	$ 699,888	$ 836,396	$ 699,888
Reserve for Unfunded Commitments	0.22%	0.20%	0.22%	0.20%

X

- Definition

Loan loss provisions, also known as valuation allowances, are an expense set aside as an allowance for potential uncollected loans and loan payments.

+ References

No definition available.

+ Details

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Balance Type:	debit
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X

- Definition

Reserve for unfunded commitments to unfunded loan commitments percentage.

+ References

No definition available.

+ Details

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X

- Definition

Unfunded loan commitments are those commitments made by a Financial institution that are contractual obligations for future funding.

+ References

No definition available.

+ Details

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Namespace Prefix:	SFST_
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X

- 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

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X

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Topic 942
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-Paragraph 1
-Subparagraph (SX 210.9-03(7)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

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