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Commitments and Contingencies (FY) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 299.6	$ 292.8
Standby letters of credit, issued by the Company	$ 3.7	$ 5.5

X

- Definition

Contractual amount for all off-balance sheet commitments.

+ References

No definition available.

+ Details

Name:	smbk_OutstandingOffBalanceSheetRisksAmountLiability
Namespace Prefix:	smbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Unused amount of commitments to extend credit to customers.

+ References

No definition available.

+ Details

Name:	us-gaap_UnusedCommitmentsToExtendCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant