Aggregate loans outstanding percentage.

No definition available.

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Namespace Prefix:	smbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Allowance for loan losses basis points.

+ References

No definition available.

+ Details

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Namespace Prefix:	smbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Finance receivable increase (decrease) in reserve.

+ References

No definition available.

+ Details

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Namespace Prefix:	smbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Financing Receivable, Modifications, Amount

+ References

No definition available.

+ Details

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

- Definition

Financing Receivable, Nonaccrual, Number Of Contracts

+ References

No definition available.

+ Details

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Namespace Prefix:	smbk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Increase (decrease) provision for loan expensed.

+ References

No definition available.

+ Details

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Namespace Prefix:	smbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of loans related to payroll protection program.

+ References

No definition available.

+ Details

Name:	smbk_NumberOfLoansRelatedToPayrollProtectionProgram
Namespace Prefix:	smbk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Properties, Other Real Estate Owned

+ References

No definition available.

+ Details

Name:	smbk_NumberOfPropertiesOtherRealEstateOwned
Namespace Prefix:	smbk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Payroll Protection Program Loans Outstanding.

+ References

No definition available.

+ Details

Name:	smbk_PayrollProtectionProgramLoansOutstanding
Namespace Prefix:	smbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of allowance for credit losses to aggregate loans.

+ References

No definition available.

+ Details

Name:	smbk_PercentageOfAllowanceForCreditLossesToAggregateLoans
Namespace Prefix:	smbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

+ Details

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

- 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

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

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

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Loans and Allowance for Loan Losses - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) loan property	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) loan property segment	Sep. 30, 2019 USD ($) loan	Dec. 31, 2019 USD ($) loan	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loan portfolio segments \| segment			5
Number of contracts \| loan			1	0
Number of contracts, subsequent payment default \| loan			0
Number of properties in other real estate owned \| property	1		1
Provision (reallocation) charged to expense	$ 2,634	$ 724	$ 8,683	$ 1,914
Increase (decrease) provision for loan expensed			6,800
Allowance for loan losses	$ 18,817	$ 9,792	$ 18,817	$ 9,792	$ 10,243	$ 16,254	$ 9,097	$ 8,275
Allowance for loan losses basis points			1.25%		1.00%
Percentage of allowance for credit losses to aggregate loans	0.78%		0.78%		0.54%
Trouble Debt Restructuring [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans that met criteria for restructured	$ 8		$ 8		$ 61
Number of contracts, nonaccrual \| loan	0		0		0
COVID-19 [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| loan			289
Number of loans related to payroll protection program \| loan	2,950		2,950
Payroll Protection Program Loans Outstanding	$ 300,800		$ 300,800
Loan modification, amount	$ 232,500		$ 232,500
Aggregate loans outstanding percentage	9.70%		9.70%
Finance receivable increase (decrease) in reserve	$ 8,300