Employee Benefits - Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions (Details) - $ / shares	12 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2021
Employee Benefits
Expected dividend yield	1.79%	1.49%	1.83%
Expected volatility	29.67%	28.02%	27.72%
Risk-free interest rate	3.79%	1.82%	1.14%
Weighted-average expected life (years)	10 years	10 years	10 years
Weighted-average fair value of options granted during the year	$ 16.68	$ 16.38	$ 9.19

Represents the Fair Value Assumptions, Expected Dividend Yield, during the indicated time period.

No definition available.

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Data Type:	dtr-types:percentItemType
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Period Type:	duration

- Definition

Represents the Fair Value Assumptions Expected Volatility Rate, during the indicated time period.

+ References

No definition available.

+ Details

Name:	smbc_FairValueAssumptionsExpectedVolatilityRate1
Namespace Prefix:	smbc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the Fair Value Assumptions Risk Free Interest Rate, during the indicated time period.

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No definition available.

+ Details

Name:	smbc_FairValueAssumptionsRiskFreeInterestRate1
Namespace Prefix:	smbc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the pure numeric value of Fair value assumptions weighted-average expected life (years), as of the indicated date.

+ References

No definition available.

+ Details

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

- Definition

Represents the per-share monetary value of Fair value assumptions weighted-average fair value of options granted during the year, as of the indicated date.

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No definition available.

+ Details

Name:	smbc_FairValueAssumptionsWeightedAverageFairValueOfOptionsGrantedDuringTheYear
Namespace Prefix:	smbc_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
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Period Type:	duration