XML 39 R28.htm IDEA: XBRL DOCUMENT
v3.25.3

Investment Securities (Details) - Schedule of gross unrealized losses on investment securities and fair market value of related securities $ in Thousands | Sep. 30, 2025 USD ($) Investments | Dec. 31, 2024 USD ($) Investments
--- | --- | ---
Corporate bonds [Member] |  |
Marketable Securities [Line Items] |  |
Available for sale Securities, Less than 12 months, Number of investments | Investments | Investments |  |
Available for sale Securities, Less than 12 months, Fair value |  |
Available for sale Securities, Less than 12 months, Unrealized losses |  |
Available for sale Securities, 12 months or longer, Number of investments | Investments | Investments | 1 | 1
Available for sale Securities, 12 months or longer, Fair value | $ 1,959 | $ 1,927
Available for sale Securities, 12 months or Longer, Unrealized losses | $ 143 | $ 194
Available for sale Securities, Total, Number of investments | Investments | Investments | 1 | 1
Available for sale Securities, Total, Fair value | $ 1,959 | $ 1,927
Available for sale Securities, Total, Unrealized losses | $ 143 | $ 194
US treasuries [Member] |  |
Marketable Securities [Line Items] |  |
Available for sale Securities, Less than 12 months, Number of investments | Investments | Investments |  |
Available for sale Securities, Less than 12 months, Fair value |  |
Available for sale Securities, Less than 12 months, Unrealized losses |  |
Available for sale Securities, 12 months or longer, Number of investments | Investments | Investments | 1 | 1
Available for sale Securities, 12 months or longer, Fair value | $ 944 | $ 908
Available for sale Securities, 12 months or Longer, Unrealized losses | $ 56 | $ 91
Available for sale Securities, Total, Number of investments | Investments | Investments | 1 | 1
Available for sale Securities, Total, Fair value | $ 944 | $ 908
Available for sale Securities, Total, Unrealized losses | $ 56 | $ 91
US government agencies [Member] |  |
Marketable Securities [Line Items] |  |
Available for sale Securities, Less than 12 months, Number of investments | Investments | Investments |  | 1
Available for sale Securities, Less than 12 months, Fair value |  | $ 2,694
Available for sale Securities, Less than 12 months, Unrealized losses |  | $ 1
Available for sale Securities, 12 months or longer, Number of investments | Investments | Investments | 9 | 9
Available for sale Securities, 12 months or longer, Fair value | $ 10,801 | $ 10,269
Available for sale Securities, 12 months or Longer, Unrealized losses | $ 1,216 | $ 1,745
Available for sale Securities, Total, Number of investments | Investments | Investments | 9 | 10
Available for sale Securities, Total, Fair value | $ 10,801 | $ 12,963
Available for sale Securities, Total, Unrealized losses | $ 1,216 | $ 1,746
State and political subdivisions [Member] |  |
Marketable Securities [Line Items] |  |
Available for sale Securities, Less than 12 months, Number of investments | Investments | Investments | 2 | 3
Available for sale Securities, Less than 12 months, Fair value | $ 953 | $ 1,436
Available for sale Securities, Less than 12 months, Unrealized losses | $ 95 | $ 153
Available for sale Securities, 12 months or longer, Number of investments | Investments | Investments | 31 | 30
Available for sale Securities, 12 months or longer, Fair value | $ 18,948 | $ 17,886
Available for sale Securities, 12 months or Longer, Unrealized losses | $ 2,203 | $ 2,912
Available for sale Securities, Total, Number of investments | Investments | Investments | 33 | 33
Available for sale Securities, Total, Fair value | $ 19,901 | $ 19,322
Available for sale Securities, Total, Unrealized losses | $ 2,298 | $ 3,065
Asset-backed securities [Member] |  |
Marketable Securities [Line Items] |  |
Available for sale Securities, Less than 12 months, Number of investments | Investments | Investments | 3 | 6
Available for sale Securities, Less than 12 months, Fair value | $ 7,877 | $ 15,828
Available for sale Securities, Less than 12 months, Unrealized losses | $ 74 | $ 83
Available for sale Securities, 12 months or longer, Number of investments | Investments | Investments | 5 | 5
Available for sale Securities, 12 months or longer, Fair value | $ 8,328 | $ 5,344
Available for sale Securities, 12 months or Longer, Unrealized losses | $ 61 | $ 28
Available for sale Securities, Total, Number of investments | Investments | Investments | 8 | 11
Available for sale Securities, Total, Fair value | $ 16,205 | $ 21,172
Available for sale Securities, Total, Unrealized losses | $ 135 | $ 111
Mortgage-backed securities [Member] |  |
Marketable Securities [Line Items] |  |
Available for sale Securities, Less than 12 months, Number of investments | Investments | Investments | 4 | 6
Available for sale Securities, Less than 12 months, Fair value | $ 6,147 | $ 8,226
Available for sale Securities, Less than 12 months, Unrealized losses | $ 49 | $ 409
Available for sale Securities, 12 months or longer, Number of investments | Investments | Investments | 65 | 61
Available for sale Securities, 12 months or longer, Fair value | $ 52,369 | $ 45,360
Available for sale Securities, 12 months or Longer, Unrealized losses | $ 6,870 | $ 8,961
Available for sale Securities, Total, Number of investments | Investments | Investments | 69 | 67
Available for sale Securities, Total, Fair value | $ 58,516 | $ 53,586
Available for sale Securities, Total, Unrealized losses | $ 6,919 | $ 9,370
Total investment securities [Member] |  |
Marketable Securities [Line Items] |  |
Available for sale Securities, Less than 12 months, Number of investments | Investments | Investments | 9 | 16
Available for sale Securities, Less than 12 months, Fair value | $ 14,977 | $ 28,184
Available for sale Securities, Less than 12 months, Unrealized losses | $ 218 | $ 646
Available for sale Securities, 12 months or longer, Number of investments | Investments | Investments | 112 | 107
Available for sale Securities, 12 months or longer, Fair value | $ 93,349 | $ 81,694
Available for sale Securities, 12 months or Longer, Unrealized losses | 10,549 | 13,931
Available for sale Securities, Total, Fair value | 108,326 | 109,878
Available for sale Securities, Total, Unrealized losses | $ 10,767 | $ 14,577
Available for sale Securities, Total, Number of investments | Investments | Investments | 121 | 123

X
- Definition Number of investments in continuous unrealized loss position. + References No definition available. + Details
Name: | SFST_AvailableForSaleSecuritiesTotalNumberOfInvestments
Namespace Prefix: | SFST_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of investments in continuous unrealized loss position. + References No definition available. + Details
Name: | SFST_NumberOfInvestmentsInContinuousUnrealizedLossPosition
Namespace Prefix: | SFST_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of investments in continuous unrealized loss position, less than twelve months. + References No definition available. + Details
Name: | SFST_NumberOfInvestmentsInContinuousUnrealizedLossPositionLessThanTwelveMonths
Namespace Prefix: | SFST_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of investments in continuous unrealized loss position twelve months or longer. + References No definition available. + Details
Name: | SFST_NumberOfInvestmentsInContinuousUnrealizedLossPositionTwelveMonthsOrLonger
Namespace Prefix: | SFST_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479081/326-30-55-8 Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-7 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-5 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-7 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-5 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479081/326-30-55-8 Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-7 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-5 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-7 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-5 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479081/326-30-55-8 Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-6 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-4 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-6 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (a)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-4 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_MarketableSecuritiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=SFST_CorporateBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=SFST_USTreasuresMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_AgencySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_SecuritiesInvestmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |