Premises and Equipment - Lessor Agreements (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Premises and Equipment
Income recognized from lessor agreements	$ 82,000	$ 80,000	$ 238,000	$ 242,000

Represents the monetary amount of Income Recognized From Lessor Agreements, during the indicated time period.

No definition available.

Name:	smbc_IncomeRecognizedFromLessorAgreements
Namespace Prefix:	smbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration