Amortization term of agriculture loans if 80% of loan-to-value ratio.

No definition available.

Name:	smbc_AgricultureLoansAmortizationPeriodIfEightyPercentOfLoanToValueRatio
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortization term of agriculture loans if 75% of loan-to-value ratio.

+ References

No definition available.

+ Details

Name:	smbc_AgricultureLoansAmortizationPeriodIfSeventyFivePercentOfLoanToValueRatio
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of loans, for which a modification had been agreed to.

+ References

No definition available.

+ Details

Name:	smbc_AmountOfLoansModifiedForOtherThanTdr
Namespace Prefix:	smbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the average term of construction loan.

+ References

No definition available.

+ Details

Name:	smbc_AverageTermOfConstructionLoan
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maturities of construction loans related to multi family and commercial residential real estate.

+ References

No definition available.

+ Details

Name:	smbc_ConstructionLoansMultiFamilyResidentialAndCommercialRealEstateMaturities
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maturities of construction loans related to single family residential real estate.

+ References

No definition available.

+ Details

Name:	smbc_ConstructionLoansSingleFamilyResidentialRealEstateMaturities
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortization term of fixed-rate and adjustable rate mortgage loans.

+ References

No definition available.

+ Details

Name:	smbc_FixedRateAndAdjustableRateMortgageLoansAmortizationPeriod
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the incremental period that the loan maturity can be extended to.

+ References

No definition available.

+ Details

Name:	smbc_LoanMaturityExtensionsIncrementalPeriods
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of adjusted interest rate applicability on loans.

+ References

No definition available.

+ Details

Name:	smbc_LoansAdjustedInterestRateApplicabilityTerm
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortization term of loans.

+ References

No definition available.

+ Details

Name:	smbc_LoansAmortizationPeriod
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of appraised value or purchase price that loans cannot exceed.

+ References

No definition available.

+ Details

Name:	smbc_LoansCanBeTakenMaximumPercentageOfAppraisedValueOrPurchasePrice
Namespace Prefix:	smbc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of fixed interest rate applicability on loans

+ References

No definition available.

+ Details

Name:	smbc_LoansFixedInterestRateApplicabilityTerm
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the pure numeric value of Number of Loans Modified for Other Than TDR, as of the indicated date.

+ References

No definition available.

+ Details

Name:	smbc_NumberOfLoansModifiedForOtherThanTdr
Namespace Prefix:	smbc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents amount of expense (credit) related to estimated loss from loan and lease transactions, including off-balance sheet credit loss.

+ References

No definition available.

+ Details

Name:	smbc_ProvisionForLoanAndLeaseLossesIncludingOffBalanceSheetCreditLoss
Namespace Prefix:	smbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amortization term of multi family residences loans if the balloon maturities.

+ References

No definition available.

+ Details

Name:	smbc_ResidentialLoansMultiFamilyBalloonMaturitiesAmortizationPeriod
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_SingleFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_MultifamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=smbc_ConstructionPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance for Credit Losses - Classes of loans information (Details)	3 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)
Provision for credit losses, credit (charges)	$ 5,100,000	$ 305,000
Residential Real Estate.
Fixed-rate and adjustable-rate mortgage (ARM) loans amortization period (in years)	30 years
Residential Real Estate. \| Single Family
Maximum percentage of appraised value or purchase price that loans cannot exceed	90.00%
Residential Real Estate. \| Multifamily
Amortization period of loans	25 years
Amortization period of multi-family residential loans if balloon maturities	10 years
Commercial
Amortization period of loans	25 years
Term of fixed interest applicability on loans	10 years
Term of variable interest applicability on loans	7 years
Agricultural real estate terms if 80% loan-to-value ratio	25 years
Agricultural real estate terms if 75% loan-to-value ratio	30 years
Residential Real Estate
Amortization period of loans	30 years
Residential Real Estate \| Minimum
Maturities of single-family residential construction loans	6 months
Residential Real Estate \| Maximum
Maturities of single-family residential construction loans	12 months
Commercial Real Estate
Amortization period of loans	25 years
Construction Real Estate
Average term of construction loans	12 months
Construction Real Estate \| Minimum
Maturities of multifamily or commercial construction loans	12 months
Construction Real Estate \| Maximum
Maturities of multifamily or commercial construction loans	36 months
Consumer loans
Amortization period of loans	66 months
Consumer loans \| Home Equity Loan
Maximum percentage of appraised value or purchase price that loans cannot exceed	100.00%
Amortization period of loans	10 years
Consumer loans \| Automobile loans
Maximum percentage of appraised value or purchase price that loans cannot exceed	100.00%
Amortization period of loans	66 months
Commercial loans
Amortization period of loans	5 years
Amortization period of multi-family residential loans if balloon maturities	1 year
Modifications for the purpose of extending the maturity date \| Construction Real Estate
Incremental period that the loan maturity can be extended to	3 months
Number of construction loans outstanding, for which a modification had been agreed to	53		57
Construction loans outstanding, for which a modification had been agreed to	$ 32,600,000		$ 13,800,000