Available for Sale Securities - Other Securities Policy: Pooled Trust Preferred Securities (Details)	12 Months Ended
Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)
Available for Sale Securities
Number of Pooled Trust Preferred Securities	2
Fair Value of Pooled Trust Preferred Securities Held	$ 794,000
Unrealized Losses on Pooled Trust Preferred Securities in a Continuous Unrealized Loss Position for 12 Months or More	184,000
Credit losses recognized on investments	$ 0	$ 0

Represents the monetary amount of Fair Value of Pooled Trust Preferred Securities Held, as of the indicated date.

No definition available.

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

- Definition

Represents the pure numeric value of Number of Pooled Trust Preferred Securities, as of the indicated date.

+ References

No definition available.

+ Details

Name:	smbc_NumberOfPooledTrustPreferredSecurities
Namespace Prefix:	smbc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the monetary amount of Unrealized Losses on Pooled Trust Preferred Securities in a Continuous Unrealized Loss Position for 12 Months or More, as of the indicated date.

+ References

No definition available.

+ Details

Name:	smbc_UnrealizedLossesOnPooledTrustPreferredSecuritiesInAContinuousUnrealizedLossPositionFor12MonthsOrMore
Namespace Prefix:	smbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Amount of expense related to credit loss from transactions other than loan and lease transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(11))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

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