Loans and Allowance for Loan Losses (Details 1) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Summary of balance of the allowance for loan losses and the recorded investment in loans
Beginning balance	$ 8,167	$ 7,930
Charge offs	(60)	(20)
Recoveries	14	9
Provision		300
Ending balance	8,121	8,219
Allowance: Ending balance: individually evaluated for impairment	90		$ 138
Allowance: Ending balance: collectively evaluated for impairment	8,031		8,029
Loans: Ending balance: individually evaluated for impairment	3,506		3,284
Loans: Ending balance: collectively evaluated for impairment	778,396		768,000
Commercial & industrial [Member]
Summary of balance of the allowance for loan losses and the recorded investment in loans
Beginning balance	1,435	823
Charge offs	(48)
Recoveries
Provision	(53)	155
Ending balance	1,334	978
Allowance: Ending balance: individually evaluated for impairment			61
Allowance: Ending balance: collectively evaluated for impairment	1,334		1,374
Loans: Ending balance: individually evaluated for impairment	948		700
Loans: Ending balance: collectively evaluated for impairment	134,632		126,341
Commercial real estate [Member]
Summary of balance of the allowance for loan losses and the recorded investment in loans
Beginning balance	2,923	3,779
Charge offs		(19)
Recoveries		3
Provision	346	(90)
Ending balance	3,269	3,673
Allowance: Ending balance: individually evaluated for impairment
Allowance: Ending balance: collectively evaluated for impairment	3,269		2,923
Loans: Ending balance: individually evaluated for impairment	212		283
Loans: Ending balance: collectively evaluated for impairment	342,259		340,508
Agricultural [Member]
Summary of balance of the allowance for loan losses and the recorded investment in loans
Beginning balance	482	505
Charge offs
Recoveries
Provision	(16)	12
Ending balance	466	517
Allowance: Ending balance: individually evaluated for impairment
Allowance: Ending balance: collectively evaluated for impairment	466		482
Loans: Ending balance: individually evaluated for impairment
Loans: Ending balance: collectively evaluated for impairment	50,620		52,012
Residential real estate [Member]
Summary of balance of the allowance for loan losses and the recorded investment in loans
Beginning balance	2,567	2,129
Charge offs
Recoveries		1
Provision	(251)	229
Ending balance	2,316	2,359
Allowance: Ending balance: individually evaluated for impairment	89		73
Allowance: Ending balance: collectively evaluated for impairment	2,227		2,494
Loans: Ending balance: individually evaluated for impairment	2,308		2,111
Loans: Ending balance: collectively evaluated for impairment	189,349		184,993
Consumer [Member]
Summary of balance of the allowance for loan losses and the recorded investment in loans
Beginning balance	760	694
Charge offs	(12)	(1)
Recoveries	14	5
Provision	(26)	(6)
Ending balance	736	$ 692
Allowance: Ending balance: individually evaluated for impairment	1		4
Allowance: Ending balance: collectively evaluated for impairment	735		756
Loans: Ending balance: individually evaluated for impairment	38		190
Loans: Ending balance: collectively evaluated for impairment	$ 61,536		$ 64,146

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_CommercialAndIndustrialPortfolioSegmentMember
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=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: