Available for Sale Securities - Other Securities Policy: Pooled Trust Preferred Securities (Details)	3 Months Ended	9 Months Ended
Mar. 31, 2023 USD ($) security	Mar. 31, 2022 USD ($)	Mar. 31, 2023 USD ($) security	Mar. 31, 2022 USD ($)
Available for Sale Securities
Number of Pooled Trust Preferred Securities \| security	2		2
Fair Value of Pooled Trust Preferred Securities Held	$ 770,000		$ 770,000
Unrealized Losses on Pooled Trust Preferred Securities in a Continuous Unrealized Loss Position for 12 Months or More	209,000		209,000
Credit losses recognized on investments	$ 0	$ 0	$ 0	$ 0

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

No definition available.

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Data Type:	xbrli:monetaryItemType
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- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	smbc_
Data Type:	xbrli:integerItemType
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

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

- References

No definition available.

+ Details

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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 https://asc.fasb.org/extlink&oid=126954810&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 https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

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Balance Type:	debit
Period Type:	duration