Loans and Allowance for Loan Losses - Construction Lending (Details) $ in Millions	Jun. 30, 2020 USD ($) loan	Jun. 30, 2019 USD ($) loan
Number of loans modified for other than Tdr \| loan	77	59
Amount Of loans modified for other than Tdr	$ 48.8	$ 27.2
Construction Loans
Amount Of loans modified for other than Tdr	$ 4.7

Represents the pure numeric value of Number of Loans Modified for Other Than TDR, as of the indicated date.

No definition available.

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Namespace Prefix:	smbc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration