Deposits (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021
Deposits
Non-interest bearing accounts	$ 386,379	$ 358,418
NOW accounts	938,555	925,280
Money market deposit accounts	253,827	253,614
Savings accounts	238,587	230,905
Certificates	554,347	562,586
Total Deposit Accounts	2,371,695	2,330,803
TOTAL DEPOSITS	$ 2,371,695	$ 2,330,803

The amount represents certificate of deposits.

No definition available.

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- Definition

Represents the monetary amount of Total Non-Maturity Deposits, as of the indicated date.

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No definition available.

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

- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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Balance Type:	credit
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No definition available.

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Name:	us-gaap_DepositsAbstract
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- Definition

Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts.

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Name:	us-gaap_DepositsMoneyMarketDeposits
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Balance Type:	credit
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- Definition

Amount of deposits in interest-bearing transaction accounts at banks or savings and loans, that are restricted in regard to ownership and can usually only be held by individuals, nonprofit entities and governments. Negotiable order of withdrawal accounts differ from money market demand accounts as they typically have higher reserve requirements and no limit on the number of checks that can be written.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of interest bearing deposits with no stated maturity, which may include passbook and statement savings accounts and money-market deposit accounts (MMDAs).

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Name:	us-gaap_DepositsSavingsDeposits
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Balance Type:	credit
Period Type:	instant

- Definition

The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.

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+ Details

Name:	us-gaap_NoninterestBearingDepositLiabilities
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant