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Unused Lines of Credit (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2022 USD ($)
Unused Lines of Credit [Abstract] |
Lines of credit to purchase federal funds | $ 118.5
Additional borrowings under FHLB | 515.8
Unsecured interest line of credit | $ 15.0
Secured overnight financing rate | 3.50%

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- Definition Additional borrowings under Federal Home Loan Bank. + References No definition available. + Details
Name: | sfst_AdditionalBorrowingsUnderFederalHomeLoan
Namespace Prefix: | sfst_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Secured overnight financing rate. + References No definition available. + Details
Name: | sfst_SecuredOvernightFinancingRate
Namespace Prefix: | sfst_
Data Type: | dtr:percentItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | sfst_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with either short term or long term maturity that is uncollateralized (where debt is not backed by the pledge of collateral). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3255-108585 + Details
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Balance Type: | debit
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