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Unused Lines of Credit (Details) $ in Millions | Dec. 31, 2017 USD ($) linesofcredit
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Unused Lines of Credit (Textual) |
Number of lines of credit | linesofcredit | 4
Lines of credit to purchase federal funds | $ 72.0
Additional borrowings under FHLB | $ 261.9

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

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- Definition Number of lines of credit. + References No definition available. + Details
Name: | sfst_NumberOfLinesOfCredit
Namespace Prefix: | sfst_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | sfst_UnusedLinesOfCreditTextualAbstract
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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant