Loans and Allowance for Loan Losses (Details 2) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	$ 7,930	$ 7,725
Charge offs	(407)	(231)
Recoveries	44	36
Provision	600	400
Ending Balance	8,167	7,930
Allowance: Ending balance: individually evaluated for impairment	138	329
Allowance: Ending balance: collectively evaluated for impairment	8,029	7,601
Loans: Ending balance individually evaluated for impairment	3,284	3,412
Loans: Ending balance collectively evaluated for impairment	768,000	692,716
Commercial & Industrial [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	823	1,204
Charge offs	(227)	(50)
Recoveries	1	5
Provision	838	(336)
Ending Balance	1,435	823
Allowance: Ending balance: individually evaluated for impairment	61
Allowance: Ending balance: collectively evaluated for impairment	1,374	823
Loans: Ending balance individually evaluated for impairment	700
Loans: Ending balance collectively evaluated for impairment	126,341	101,554
Commercial RE & Construction [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	3,779	3,321
Charge offs	(42)	(26)
Recoveries	28	2
Provision	(842)	482
Ending Balance	2,923	3,779
Allowance: Ending balance: individually evaluated for impairment		146
Allowance: Ending balance: collectively evaluated for impairment	2,923	3,633
Loans: Ending balance individually evaluated for impairment	283	1,385
Loans: Ending balance collectively evaluated for impairment	340,508	330,769
Agricultural & farmland [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	505	347
Charge offs
Recoveries		5
Provision	(23)	153
Ending Balance	482	505
Allowance: Ending balance: individually evaluated for impairment
Allowance: Ending balance: collectively evaluated for impairment	482	505
Loans: Ending balance individually evaluated for impairment
Loans: Ending balance collectively evaluated for impairment	52,012	51,947
Residential real estate [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	2,129	1,963
Charge offs	(30)	(61)
Recoveries	2	6
Provision	466	221
Ending Balance	2,567	2,129
Allowance: Ending balance: individually evaluated for impairment	73	178
Allowance: Ending balance: collectively evaluated for impairment	2,494	1,951
Loans: Ending balance individually evaluated for impairment	2,111	1,830
Loans: Ending balance collectively evaluated for impairment	184,993	149,024
Consumer & Other [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	694	890
Charge offs	(108)	(94)
Recoveries	13	18
Provision	161	(120)
Ending Balance	760	694
Allowance: Ending balance: individually evaluated for impairment	4	5
Allowance: Ending balance: collectively evaluated for impairment	756	689
Loans: Ending balance individually evaluated for impairment	190	197
Loans: Ending balance collectively evaluated for impairment	$ 64,146	$ 59,422

A valuation allowance for financing receivables that are expected to be uncollectible.

Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

+ Details

Name:	us-gaap_ProvisionForLoanLeaseAndOtherLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sbfg_CommercialIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sbfg_CommercialReConstructionPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sbfg_AgriculturalFarmlandPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sbfg_OtherPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: