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Mortgage Servicing Rights (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2026 | Jun. 30, 2025 | Jun. 30, 2026 | Jun. 30, 2025 | Dec. 31, 2025
Mortgage Servicing Rights [Line Items] |  |  |  |  |
Specified servicing fees | $ 0.9 | $ 0.9 | $ 1.9 | $ 1.8 |
Mortgage-Backed Securities, Other [Member] |  |  |  |  |
Mortgage Servicing Rights [Line Items] |  |  |  |  |
Unpaid principal balance of mortgage loans | $ 1,500.0 |  | $ 1,500.0 |  | $ 1,480.0

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- Definition Contractually specified servicing fees . + References No definition available. + Details
Name: | sbfg_ContractuallySpecifiedServicingFees
Namespace Prefix: | sbfg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amount of unpaid principal balance of mortgage loans serviced for others. + References No definition available. + Details
Name: | sbfg_UnpaidPrincipalBalanceOfMortgageLoansServicedForOthers
Namespace Prefix: | sbfg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- 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_ParticipatingMortgageLoansLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_UnderlyingAssetClassAxis=us-gaap_MortgageBackedSecuritiesOtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |