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Related Party Transactions (Details) - Directors and executive officers, their affiliates [Member] - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Summary of loan transactions with directors, including their affiliates and executive officers |  |
Balance, beginning of year | $ 14,825 | $ 12,868
New loans | 6,843 | 5,103
Less loan payments | (6,392) | (3,146)
Balance, end of year | $ 15,276 | $ 14,825

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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: |