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v3.20.4

Related Party Transactions (Details) - Directors Affiliates and Executive Officers [Member] - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Summary of loan transactions with directors, including their affiliates and executive officers |  |
Balance, beginning of year | $ 10,891 | $ 13,969
New loans | 4,389 | 6,709
Less loan payments | (9,490) | (9,787)
Balance, end of year | $ 5,790 | $ 10,891

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- Definition Loan payments by related party. + References No definition available. + Details
Name: | sfst_LoanPaymentsRelatedParty
Namespace Prefix: | sfst_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Loan transactions with related party. + References No definition available. + Details
Name: | sfst_LoanTransactionsWithRelatedParty
Namespace Prefix: | sfst_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition New loans. + References No definition available. + Details
Name: | sfst_NewLoans
Namespace Prefix: | sfst_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=sfst_DirectorsAffiliatesAndExecutiveOfficersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |