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Derivative Financial Instruments (Details) - Schedule of summarize the effect of fair value hedging relationship recognized in the consolidated statement of income - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024
Gain (loss) on fair value hedging relationship: |  |
Hedged asset/liability | $ 257 | $ 3,688
Fair value derivative designated as hedging instrument | (256) | (3,738)
Total gain (loss) recognized in interest income on loans | $ 1 | $ (50)

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- Definition Fair value of all derivative designated as fair value hedging instruments. + References No definition available. + Details
Name: | SFST_FairValueDerivativeDesignatedAsHedgingInstrument
Namespace Prefix: | SFST_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Gain Loss On Fair Value Hedging Relationship [Abstract] + References No definition available. + Details
Name: | SFST_GainLossOnFairValueHedgingRelationshipAbstract
Namespace Prefix: | SFST_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of gain (loss) recognized in income from asset and liability measured at fair value on recurring basis using unobservable input (level 3). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInEarnings
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4C + Details
Name: | us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration