Name:	smbc_FairValueMeasurementsNonrecurringRangeOfDiscountsApplied
Namespace Prefix:	smbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the description of Fair Value Measurements Nonrecurring Unobservable Inputs, during the indicated time period.

No definition available.

Name:	smbc_FairValueMeasurementsNonrecurringUnobservableInputs
Namespace Prefix:	smbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the description of Fair Value Measurements Nonrecurring Valuation Technique, during the indicated time period.

No definition available.

Name:	smbc_FairValueMeasurementsNonrecurringValuationTechnique
Namespace Prefix:	smbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the description of Fair Value Measurements Nonrecurring Weighted Average Discount Applied, during the indicated time period.

No definition available.

Name:	smbc_FairValueMeasurementsNonrecurringWeightedAverageDiscountApplied
Namespace Prefix:	smbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the description of Fair Value Measurements Recurring Range of discounts Applied, during the indicated time period.

No definition available.

Name:	smbc_FairValueMeasurementsRecurringRangeOfDiscountsApplied
Namespace Prefix:	smbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the description of Fair Value Measurements Recurring Unobservable Inputs, during the indicated time period.

No definition available.

Name:	smbc_FairValueMeasurementsRecurringUnobservableInputs
Namespace Prefix:	smbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the description of Fair Value Measurements Recurring Valuation Technique, during the indicated time period.

No definition available.

Name:	smbc_FairValueMeasurementsRecurringValuationTechnique
Namespace Prefix:	smbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the description of Fair Value Measurements Recurring Weighted Average Discount Applied, during the indicated time period.

No definition available.

Name:	smbc_FairValueMeasurementsRecurringWeightedAverageDiscountApplied
Namespace Prefix:	smbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

No definition available.

Name:	us-gaap_AssetsFairValueDisclosureNonrecurring
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

No definition available.

Name:	us-gaap_AssetsFairValueDisclosureRecurring
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Name:	us-gaap_InvestmentTypeAxis=smbc_ImpairedLoansCollateralDependentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_InvestmentTypeAxis=us-gaap_AvailableforsaleSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	smbc_UnobservableInputsAxis=smbc_DiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	smbc_UnobservableInputsAxis=smbc_PrepaymentRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	smbc_UnobservableInputsAxis=smbc_ProjectedDefaultsAndDeferralsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	smbc_UnobservableInputsAxis=smbc_AnticipatedRecoveriesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: