Loans and Allowance for Loan Losses (Details) - Summary of impaired loan activity - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Commercial and Industrial Sector [Member]
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	$ 722	$ 575
With no related allowance recorded, Unpaid Principal Balance	1,092	802
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment	1,377	370
With no related allowance recorded, Interest Income Recognized	114	21
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment	1,000	125
With a specific allowance recorded, Unpaid Principal Balance	1,000	125
With a specific allowance recorded, Related Allowance	511	61
With a specific allowance recorded, Average Recorded Investment	823	127
With a specific allowance recorded, Interest Income Recognized	49	21
Totals:
Total Recorded Investment	1,722	700
Total Unpaid Principal Balance	2,092	927
Total Related Allowance	511	61
Total Average Recorded Investment	2,200	497
Total Interest Income Recognized	163	42
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	722	575
With no related allowance recorded, Unpaid Principal Balance	1,092	802
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment	1,377	370
With no related allowance recorded, Interest Income Recognized	114	21
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment	1,000	125
With a specific allowance recorded, Unpaid Principal Balance	1,000	125
With a specific allowance recorded, Related Allowance	511	61
With a specific allowance recorded, Average Recorded Investment	823	127
With a specific allowance recorded, Interest Income Recognized	49	21
Totals:
Total Recorded Investment	1,722	700
Total Unpaid Principal Balance	2,092	927
Total Related Allowance	511	61
Total Average Recorded Investment	2,200	497
Total Interest Income Recognized	163	42
Commercial Real Estate - Nonowner Occupied [Member]
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	196	283
With no related allowance recorded, Unpaid Principal Balance	197	283
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment	259	336
With no related allowance recorded, Interest Income Recognized	21	21
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment	1,362
With a specific allowance recorded, Unpaid Principal Balance	1,362
With a specific allowance recorded, Related Allowance	147
With a specific allowance recorded, Average Recorded Investment	1,362
With a specific allowance recorded, Interest Income Recognized	38
Totals:
Total Recorded Investment	196	283
Total Unpaid Principal Balance	197	283
Total Average Recorded Investment	259	336
Total Interest Income Recognized	21	21
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	196	283
With no related allowance recorded, Unpaid Principal Balance	197	283
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment	259	336
With no related allowance recorded, Interest Income Recognized	21	21
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment	1,362
With a specific allowance recorded, Unpaid Principal Balance	1,362
With a specific allowance recorded, Related Allowance	147
With a specific allowance recorded, Average Recorded Investment	1,362
With a specific allowance recorded, Interest Income Recognized	38
Totals:
Total Recorded Investment	196	283
Total Unpaid Principal Balance	197	283
Total Average Recorded Investment	259	336
Total Interest Income Recognized	21	21
Agricultural & farmland [Member]
With no related allowance recorded:
With no related allowance recorded, Recorded Investment
With no related allowance recorded, Unpaid Principal Balance
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment
With no related allowance recorded, Interest Income Recognized
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment
With a specific allowance recorded, Unpaid Principal Balance
With a specific allowance recorded, Related Allowance
With a specific allowance recorded, Average Recorded Investment
With a specific allowance recorded, Interest Income Recognized
Totals:
Total Recorded Investment
Total Unpaid Principal Balance
Total Related Allowance
Total Average Recorded Investment
Total Interest Income Recognized
With no related allowance recorded:
With no related allowance recorded, Recorded Investment
With no related allowance recorded, Unpaid Principal Balance
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment
With no related allowance recorded, Interest Income Recognized
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment
With a specific allowance recorded, Unpaid Principal Balance
With a specific allowance recorded, Related Allowance
With a specific allowance recorded, Average Recorded Investment
With a specific allowance recorded, Interest Income Recognized
Totals:
Total Recorded Investment
Total Unpaid Principal Balance
Total Related Allowance
Total Average Recorded Investment
Total Interest Income Recognized
Residential Portfolio Segment [Member]
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	1,621	1,249
With no related allowance recorded, Unpaid Principal Balance	1,687	1,292
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment	2,001	1,995
With no related allowance recorded, Interest Income Recognized	106	91
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment	653	862
With a specific allowance recorded, Unpaid Principal Balance	653	888
With a specific allowance recorded, Related Allowance	68	73
With a specific allowance recorded, Average Recorded Investment	666	426
With a specific allowance recorded, Interest Income Recognized	31	20
Totals:
Total Recorded Investment	2,274	2,111
Total Unpaid Principal Balance	2,340	2,180
Total Related Allowance	68	73
Total Average Recorded Investment	2,667	2,421
Total Interest Income Recognized	137	111
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	1,621	1,249
With no related allowance recorded, Unpaid Principal Balance	1,687	1,292
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment	2,001	1,995
With no related allowance recorded, Interest Income Recognized	106	91
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment	653	862
With a specific allowance recorded, Unpaid Principal Balance	653	888
With a specific allowance recorded, Related Allowance	68	73
With a specific allowance recorded, Average Recorded Investment	666	426
With a specific allowance recorded, Interest Income Recognized	31	20
Totals:
Total Recorded Investment	2,274	2,111
Total Unpaid Principal Balance	2,340	2,180
Total Related Allowance	68	73
Total Average Recorded Investment	2,667	2,421
Total Interest Income Recognized	137	111
Home Equity Line of Credit [Member]
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	16	20
With no related allowance recorded, Unpaid Principal Balance	16	20
With no related allowance recorded, Average Recorded Investment	18	21
With no related allowance recorded, Interest Income Recognized	1	1
Totals:
Total Recorded Investment	16	20
Total Unpaid Principal Balance	16	20
Total Average Recorded Investment	18	21
Total Interest Income Recognized	1	1
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	16	20
With no related allowance recorded, Unpaid Principal Balance	16	20
With no related allowance recorded, Average Recorded Investment	18	21
With no related allowance recorded, Interest Income Recognized	1	1
Totals:
Total Recorded Investment	16	20
Total Unpaid Principal Balance	16	20
Total Average Recorded Investment	18	21
Total Interest Income Recognized	1	1
Consumer Portfolio Segment [Member]
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	15	93
With no related allowance recorded, Unpaid Principal Balance	15	93
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment	19	104
With no related allowance recorded, Interest Income Recognized	1	7
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment		77
With a specific allowance recorded, Unpaid Principal Balance		77
With a specific allowance recorded, Related Allowance		4
With a specific allowance recorded, Average Recorded Investment		91
With a specific allowance recorded, Interest Income Recognized		6
Totals:
Total Recorded Investment	15	170
Total Unpaid Principal Balance	15	170
Total Related Allowance		4
Total Average Recorded Investment	19	195
Total Interest Income Recognized	1	13
With no related allowance recorded:
With no related allowance recorded, Recorded Investment	15	93
With no related allowance recorded, Unpaid Principal Balance	15	93
With no related allowance recorded, Related Allowance
With no related allowance recorded, Average Recorded Investment	19	104
With no related allowance recorded, Interest Income Recognized	1	7
With a specific allowance recorded:
With a specific allowance recorded, Recorded Investment		77
With a specific allowance recorded, Unpaid Principal Balance		77
With a specific allowance recorded, Related Allowance		4
With a specific allowance recorded, Average Recorded Investment		91
With a specific allowance recorded, Interest Income Recognized		6
Totals:
Total Recorded Investment	15	170
Total Unpaid Principal Balance	15	170
Total Related Allowance		4
Total Average Recorded Investment	19	195
Total Interest Income Recognized	1	$ 13
Commercial Real Estate [Member]
Totals:
Total Recorded Investment	1,362
Total Unpaid Principal Balance	1,362
Total Related Allowance	147
Total Average Recorded Investment	1,362
Total Interest Income Recognized	38
Totals:
Total Recorded Investment	1,362
Total Unpaid Principal Balance	1,362
Total Related Allowance	147
Total Average Recorded Investment	1,362
Total Interest Income Recognized	$ 38

Amount of related allowance for which there is no related allowance for credit losses.

No definition available.

Name:	sbfg_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordRelatedAllowance
Namespace Prefix:	sbfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Impaired Financing Receivable with specific allowance recorded Related Allowance.

+ References

No definition available.

+ Details

Name:	sbfg_ImpairedFinancingReceivableWithSpecificAllowanceRecordedRelatedAllowance
Namespace Prefix:	sbfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	sbfg_TotalsAbstract
Namespace Prefix:	sbfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	sbfg_TotalsAbstract0
Namespace Prefix:	sbfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	sbfg_WithASpecificAllowanceRecordedAbstract
Namespace Prefix:	sbfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	sbfg_WithASpecificAllowanceRecordedAbstract0
Namespace Prefix:	sbfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	sbfg_WithNoRelatedAllowanceRecordedAbstract
Namespace Prefix:	sbfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	sbfg_WithNoRelatedAllowanceRecordedAbstract0
Namespace Prefix:	sbfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

+ Details

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

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

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

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953550-111524

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

+ Details

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

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
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:

- Details

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