Organization and Summary of Significant Accounting Policies - Non-Employee Directors' Retirement (Details)	12 Months Ended
Jun. 30, 2026
Organization and Summary of Significant Accounting Policies
Non-Employee directors' retirement, payments in equal annual installments, period	5 years

Represents the period for the benefit payments to be made in equal annual installments.

No definition available.

Name:	smbc_NonEmployeeDirectorsRetirementAwardAwardPeriod
Namespace Prefix:	smbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration