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

Amortization term of loans if the balloon maturities.

+ References

No definition available.

+ Details

Name:	smbc_BalloonMaturitiesAmortizationPeriod
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

The percentage of the property's appraised value that is being financed by the loan of the entity during the reporting period.

+ References

No definition available.

+ Details

Name:	smbc_LoanToValuePercentage
Namespace Prefix:	smbc_
Data Type:	dtr-types:percentItemType
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 estimated value of property that loans cannot exceed.

+ References

No definition available.

+ Details

Name:	smbc_LoansCanBeTakenMaximumPercentageOfAppraisedValueOrEstimatedValueOfProperty
Namespace Prefix:	smbc_
Data Type:	dtr-types:percentItemType
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 term of loan.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

+ Details

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

- Definition

Amount of allowance for credit loss on financing receivable evaluated on collective basis. Excludes financing receivable evaluated on individual basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.5.a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480418/310-10-S99-4

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-11B

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 30
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479391/326-20-30-2

+ Details

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

- Definition

Amount of allowance for credit loss on financing receivable evaluated on individual basis. Excludes financing receivable evaluated on collective basis.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

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

- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

+ Details

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

- Definition

Amount, excluding accrued interest, of allowance for credit loss at acquisition date of financing receivable purchased with credit deterioration. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 19
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-19

+ Details

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

- Definition

Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=smbc_CitizensBancsharesCo.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=smbc_AgricultureProductionPortfolioMember
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_AutomobileLoanMember
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=srt_OtherPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_ClassOfFinancingReceivableTypeOfBorrowerAxis=us-gaap_CommercialBorrowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ClassOfFinancingReceivableTypeOfBorrowerAxis=us-gaap_ConsumerBorrowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=srt_MultifamilyMember
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:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_StatementScenarioAxis=smbc_ScenarioOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=smbc_ScenarioTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance for Credit Losses - Risk characteristics applicable to each class of the loan portfolio (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 20, 2023	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)		$ 4,100,768	$ 3,850,035
Allowance for credit losses, loans		5,847	6,625	$ 14,131
Provision (recovery) for off balance sheet credit exposure		676	(3,025)	2,930
Allowance for credit loss of individually evaluated loans		8,200	10,900
Allowance for credit loss of Non-individually evaluated loans		$ 43,400	41,600
Citizens Bancshares Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses for purchased credit deteriorated (PCD)	$ 1,121
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans		5 years
Total loans (before deferred loan fees, net)		$ 510,259	450,147
Allowance for credit losses, loans		2,160	1,356	1,492
Provision (recovery) for off balance sheet credit exposure		292	52	310
Agriculture production
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)		206,128	175,968
Allowance for credit losses, loans		3,589	53	(11)
Provision (recovery) for off balance sheet credit exposure		(37)	(70)	(111)
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)		55,387	59,671
Allowance for credit losses, loans		698	400	302
Provision (recovery) for off balance sheet credit exposure		$ (12)	(4)	14
Consumer \| Automobile loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of appraised value or purchase price that loans cannot exceed		100.00%
Amortization period of loans		66 months
Consumer \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans		66 months
All other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)		$ 5,102	3,981
Allowance for credit losses, loans		(13)	(4)	7
Provision (recovery) for off balance sheet credit exposure		8	(10)	10
Secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)		$ 3,323,892	3,160,268
Secured by real estate \| 1-4 residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of appraised value or purchase price that loans cannot exceed		90.00%
Total loans (before deferred loan fees, net)		$ 992,445	925,397
Allowance for credit losses, loans		(211)	1,067	2,044
Provision (recovery) for off balance sheet credit exposure		$ 62	14	19
Secured by real estate \| 1-4 residential real estate \| Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of appraised value or estimated value of property		90.00%
Term of loan		10 years
Secured by real estate \| 1-4 residential real estate \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fixed-rate and adjustable-rate mortgage (ARM) loans amortization period (in years)		30 years
Secured by real estate \| Commercial Real Estate \| Non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of appraised value or purchase price that loans cannot exceed		80.00%
Total loans (before deferred loan fees, net)		$ 888,317	899,770
Term of variable interest applicability on loans		7 years
Allowance for credit losses, loans		$ (3,014)	5,688	2,718
Provision (recovery) for off balance sheet credit exposure		$ (19)	(1)	(48)
Secured by real estate \| Commercial Real Estate \| Non-owner occupied \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans		25 years
Term of fixed interest applicability on loans		10 years
Secured by real estate \| Commercial Real Estate \| Owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans (before deferred loan fees, net)		$ 442,984	427,476
Allowance for credit losses, loans		(172)	(353)	2,274
Provision (recovery) for off balance sheet credit exposure		$ 25	(46)	104
Secured by real estate \| Multi-family real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of appraised value or purchase price that loans cannot exceed		85.00%
Total loans (before deferred loan fees, net)		$ 422,758	384,564
Allowance for credit losses, loans		(1,165)	(880)	4,749
Provision (recovery) for off balance sheet credit exposure		$ (31)	15	1
Secured by real estate \| Multi-family real estate \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans		25 years
Amortization term of ballon maturity		10 years
Secured by real estate \| Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans		25 years
Total loans (before deferred loan fees, net)		$ 332,405	290,541
Incremental period that the loan maturity can be extended to		3 months
Allowance for credit losses, loans		$ 1,888	(242)	134
Provision (recovery) for off balance sheet credit exposure		$ 367	(2,985)	2,654
Secured by real estate \| Construction and land development \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturities of single-family residential construction loans		6 months
Maturities of multifamily or commercial construction loans		12 months
Secured by real estate \| Construction and land development \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans		30 years
Maturities of single-family residential construction loans		12 months
Maturities of multifamily or commercial construction loans		36 months
Secured by real estate \| Agriculture real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization period of loans		1 year
Total loans (before deferred loan fees, net)		$ 244,983	232,520
Agricultural real estate terms if 75% loan-to-value ratio		30 years
Allowance for credit losses, loans		$ 2,087	(460)	422
Provision (recovery) for off balance sheet credit exposure		$ 21	$ 10	$ (23)
Secured by real estate \| Agriculture real estate \| Scenario one
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan to value percentage		80.00%
Secured by real estate \| Agriculture real estate \| Scenario two
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan to value percentage		75.00%
Secured by real estate \| Agriculture real estate \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Agricultural real estate terms if 80% loan-to-value ratio		25 years