Deposits (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Jun. 30, 2022
Non-interest bearing accounts	$ 597,600	$ 426,929
NOW accounts	1,328,423	1,171,620
Money market deposit accounts	452,728	303,612
Savings accounts	282,753	274,283
Certificates	1,064,036	638,631
TOTAL NON-MATURITY DEPOSITS	2,661,504	2,176,444
TOTAL DEPOSITS	3,725,540	2,815,075
0.00-.99%
Certificates	92,533	408,479
1.00-1.99%
Certificates	109,564	171,997
2.00-2.99%
Certificates	186,538	51,692
3.00-3.99%
Certificates	109,780	6,298
4.00-4.99%
Certificates	472,546	$ 165
5.00 - 5.99%
Certificates	93,057
6.00% and above
Certificates	$ 18

The amount represents certificate of deposits.

No definition available.

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

- Definition

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

+ References

No definition available.

+ Details

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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

- 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.

+ References

+ Details

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

- 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.

+ References

+ Details

Name:	us-gaap_DepositsNegotiableOrderOfWithdrawalNOW
Namespace Prefix:	us-gaap_
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).

+ References

+ Details

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

- Definition

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

+ References

+ Details

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

- Details

Name:	smbc_RangeOnRateOfCertificatesAxis=smbc_N00099Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	smbc_RangeOnRateOfCertificatesAxis=smbc_N100199Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	smbc_RangeOnRateOfCertificatesAxis=smbc_N200299Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	smbc_RangeOnRateOfCertificatesAxis=smbc_N300399Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	smbc_RangeOnRateOfCertificatesAxis=smbc_N400499Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	smbc_RangeOnRateOfCertificatesAxis=smbc_InterestRate5Point00To5Point99PercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	smbc_RangeOnRateOfCertificatesAxis=smbc_InterestRateSixPointZeroAeroAndAbovePercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: