Disclosures About Fair Value of Assets and Liabilities (Details 2) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Collateral-dependent impaired loans [Member]
Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 982	$ 786
Fair Value Measurements, Valuation Techniques	Market comparable properties Discounted cash flow	Market comparable properties Discounted cash flow
Collateral-dependent impaired loans [Member] \| Comparability Adjustments Percent [Member]
Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements
Fair Value Measurements Unobservable Input Description	Comparability adjustments (%)	Comparability adjustments (%)
Fair Value Input Interest Rate
Mortgage servicing rights [Member]
Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 1,490	$ 1,993
Mortgage servicing rights [Member] \| Discount Rate [Member]
Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements
Fair Value Measurements Unobservable Input Description	Discount Rate	Discount Rate
Fair Value Input Interest Rate	9.65%	9.65%
Mortgage servicing rights [Member] \| Constant Prepayment Rate [Member]
Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements
Fair Value Measurements Unobservable Input Description	Constant prepayment rate	Constant prepayment rate
Fair Value Input Interest Rate	7.51%	7.61%
Mortgage servicing rights [Member] \| T and I Earnings Credit [Member]
Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements
Fair Value Measurements Unobservable Input Description	T&I earnings credit	T&I earnings credit
Fair Value Input Interest Rate	2.13%	1.60%
Mortgage servicing rights [Member] \| P and I Earnings Credit [Member]
Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements
Fair Value Measurements Unobservable Input Description	P&I earnings credit	P&I earnings credit
Fair Value Input Interest Rate	1.56%	0.76%
Mortgage servicing rights [Member] \| Inflation For Cost Of Servicing [Member]
Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements
Fair Value Measurements Unobservable Input Description	Inflation for cost of servicing	Inflation for cost of servicing
Fair Value Input Interest Rate	1.50%	1.50%

Reflects the interest rate percentage.

No definition available.

Name:	sbfg_FairValueInputInterestRate
Namespace Prefix:	sbfg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the unobservable inputs used in the valuation of investment assets by the entity.

+ References

No definition available.

+ Details

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

- Definition

Quantitative information about unobservable inputs used in recurring and nonrecurring fair value measurements.

+ References

No definition available.

+ Details

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

- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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

- Definition

Description of the inputs and valuation technique(s) used to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=sbfg_CollateralDependentImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sbfg_UnobservableInputsAxis=sbfg_ComparabilityAdjustmentsPercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=sbfg_MortgageServicingRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sbfg_UnobservableInputsAxis=sbfg_DiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sbfg_UnobservableInputsAxis=sbfg_ConstantPrepaymentRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sbfg_UnobservableInputsAxis=sbfg_TAndIEarningsCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sbfg_UnobservableInputsAxis=sbfg_PAndIEarningsCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sbfg_UnobservableInputsAxis=sbfg_InflationForCostOfServicingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: