Organization and Summary of Significant Accounting Policies - New Accounting Pronouncements (Details)	12 Months Ended
Jun. 30, 2020
Minimum
Increase in estimated ACL (as a percent)	27.00%
ACL expected percentage	1.48%
Maximum
Increase in estimated ACL (as a percent)	35.00%
ACL expected percentage	1.57%

Represents the allownace for credit losses (ACL) estimated percentage of occurence , upon adoption of the new accounting standards.

No definition available.

Name:	smbc_AllowanceForCreditLossesEstimatedPercentageUponAdoption
Namespace Prefix:	smbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration