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Commitments and Contingent Liabilities (Q2) (Details) - USD ($) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Line of Credit Facility [Line Items] |  |
Commitments to extend credit | $ 299.6 | $ 292.8
Standby letters of credit | $ 3.7 | $ 5.5
Standby Letters of Credit [Member] |  |
Line of Credit Facility [Line Items] |  |
Standby letter of credit term, or less | 2 years |

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
- Definition Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_LineOfCreditFacilityExpirationPeriod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LineOfCreditFacilityLineItems
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

X
- Details
Name: | us-gaap_CreditFacilityAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |