Loans and Allowance for Loan Losses (Details 2) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	$ 7,725	$ 6,990	$ 6,771
Charge offs	(231)	(501)	(952)
Recoveries	36	486	71
Provision	400	750	1,100
Ending Balance	7,930	7,725	6,990
Allowance: Ending balance: individually evaluated for impairment	329	300	1,963
Allowance: Ending balance: collectively evaluated for impairment	7,601	7,425	5,027
Loans: Ending balance individually evaluated for impairment	3,412	3,795	8,057
Loans: Ending balance collectively evaluated for impairment	692,716	640,303	549,558
Commercial & Industrial [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	1,204	914	1,630
Charge offs	(50)	(135)	(497)
Recoveries	5	408	26
Provision	(336)	17	(245)
Ending Balance	823	1,204	914
Allowance: Ending balance: individually evaluated for impairment		50
Allowance: Ending balance: collectively evaluated for impairment	823	1,154	914
Loans: Ending balance individually evaluated for impairment		50	126
Loans: Ending balance collectively evaluated for impairment	101,554	108,702	86,416
Commercial RE & Construction [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	3,321	3,886	2,857
Charge offs	(26)	(241)	(303)
Recoveries	2	5	3
Provision	482	(329)	1,329
Ending Balance	3,779	3,321	3,886
Allowance: Ending balance: individually evaluated for impairment	146	119	1,759
Allowance: Ending balance: collectively evaluated for impairment	3,633	3,202	2,127
Loans: Ending balance individually evaluated for impairment	1,385	1,578	5,754
Loans: Ending balance collectively evaluated for impairment	330,769	282,506	236,454
Agricultural & Farmland [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	347	204	208
Charge offs
Recoveries	5	12	3
Provision	153	131	(7)
Ending Balance	505	347	204
Allowance: Ending balance: individually evaluated for impairment
Allowance: Ending balance: collectively evaluated for impairment	505	347	204
Loans: Ending balance individually evaluated for impairment
Loans: Ending balance collectively evaluated for impairment	51,947	52,475	43,835
Residential Real Estate [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	1,963	1,312	1,308
Charge offs	(61)	(20)	(56)
Recoveries	6	2	29
Provision	221	669	31
Ending Balance	2,129	1,963	1,312
Allowance: Ending balance: individually evaluated for impairment	178	124	167
Allowance: Ending balance: collectively evaluated for impairment	1,951	1,839	1,145
Loans: Ending balance individually evaluated for impairment	1,830	1,919	1,713
Loans: Ending balance collectively evaluated for impairment	149,024	140,533	129,093
Consumer & Other [Member]
Summary of allowance for loan losses and recorded investment in loans based on portfolio segment and impairment method
Beginning balance	890	674	768
Charge offs	(94)	(105)	(96)
Recoveries	18	59	10
Provision	(120)	262	(8)
Ending Balance	694	890	674
Allowance: Ending balance: individually evaluated for impairment	5	7	37
Allowance: Ending balance: collectively evaluated for impairment	689	883	637
Loans: Ending balance individually evaluated for impairment	197	248	464
Loans: Ending balance collectively evaluated for impairment	$ 59,422	$ 56,087	$ 53,760

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://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&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: