Regulatory Matters (Regulatory Capital Levels) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
SmartFinancial, Inc. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (to Risk-Weighted Assets), Actual Amount	$ 329,431	$ 287,937
Tier 1 Capital (to Risk-Weighted Assets), Actual Amount	271,739	238,433
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Actual Amount	271,739	238,433
Tier 1 Capital (to Average Assets), Actual Amount	$ 271,739	$ 238,433
Total Capital (to Risk-Weighted Assets), Actual Ratio (as a percent)	14.07%	14.02%
Tier 1 Capital (to Risk-Weighted Assets), Actual Ratio (as a percent)	11.61%	11.61%
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Actual Ratio (as a percent)	11.61%	11.61%
Tier 1 Capital (to Average Assets), Actual Ratio (as a percent)	8.70%	10.34%
Total Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Amount	$ 187,303	$ 164,313
Tier 1 Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Amount	140,477	123,235
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Amount	105,358	92,426
Tier 1 Capital (to Average Assets), Minimum for capital adequacy purposes Amount	$ 125,002	$ 92,258
Total Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Ratio (as a percent)	8.00%	8.00%
Tier 1 Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Ratio (as a percent)	6.00%	6.00%
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Ratio (as a percent)	4.50%	4.50%
Tier 1 Capital (to Average Assets), Minimum for capital adequacy purposes Ratio (as a percent)	4.00%	4.00%
Smart Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (to Risk-Weighted Assets), Actual Amount	$ 317,660	$ 273,432
Tier 1 Capital (to Risk-Weighted Assets), Actual Amount	299,314	263,189
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Actual Amount	299,314	263,189
Tier 1 Capital (to Average Assets), Actual Amount	$ 299,314	$ 263,189
Total Capital (to Risk-Weighted Assets), Actual Ratio (as a percent)	13.57%	13.31%
Tier 1 Capital (to Risk-Weighted Assets), Actual Ratio (as a percent)	12.78%	12.81%
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Actual Ratio (as a percent)	12.78%	12.81%
Tier 1 Capital (to Average Assets), Actual Ratio (as a percent)	9.58%	11.41%
Total Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Amount	$ 187,294	$ 164,305
Tier 1 Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Amount	140,470	123,229
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Amount	105,353	92,422
Tier 1 Capital (to Average Assets), Minimum for capital adequacy purposes Amount	$ 124,969	$ 92,254
Total Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Ratio (as a percent)	8.00%	8.00%
Tier 1 Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Ratio (as a percent)	6.00%	6.00%
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Minimum for capital adequacy purposes Ratio (as a percent)	4.50%	4.50%
Tier 1 Capital (to Average Assets), Minimum for capital adequacy purposes Ratio (as a percent)	4.00%	4.00%
Total Capital (to Risk-Weighted Assets), Minimum to be well capitalized under prompt corrective action provisions Amount	$ 234,117	$ 205,382
Tier 1 Capital (to Risk-Weighted Assets), Minimum to be well capitalized under prompt corrective action provisions Amount	187,294	164,305
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Minimum to be well capitalized under prompt corrective action provisions Amount	152,176	133,498
Tier 1 Capital (to Average Assets), Minimum to be well capitalized under prompt corrective action provisions Amount	$ 156,212	$ 115,317
Total Capital (to Risk-Weighted Assets), Minimum to be well capitalized under prompt corrective action provisions Ratio (as a percent)	10.00%	10.00%
Tier 1 Capital (to Risk-Weighted Assets), Minimum to be well capitalized under prompt corrective action provisions Ratio (as a percent)	8.00%	8.00%
Common Equity Tier 1 Capital (to Risk-Weighted Assets), Minimum to be well capitalized under prompt corrective action provisions Ratio (as a percent)	6.50%	6.50%
Tier 1 Capital (to Average Assets), Minimum to be well capitalized under prompt corrective action provisions Ratio (as a percent)	5.00%	5.00%

Common equity Tier 1 Risk Based Capital as defined in the regulations.

No definition available.

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

- Definition

The minimum amount of common equity Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

No definition available.

+ Details

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

- Definition

The minimum common equity Tier One Capital Ratio (Common equity Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

No definition available.

+ Details

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

- Definition

The amount of common equity Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

+ References

No definition available.

+ Details

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

- Definition

The Common equity Tier 1 capital ratio (common equity Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

No definition available.

+ Details

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

- Definition

Common equity Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

No definition available.

+ Details

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

- Definition

The amount of total capital as defined in the regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=d3e65071-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=d3e65071-112826

+ Details

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

- Definition

The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

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

- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958570-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=d3e65071-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

+ Details

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

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

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

- Definition

Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

+ References

+ Details

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

- Definition

The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

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

- Definition

The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=d3e65071-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958570-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

+ References

+ Details

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

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Leverage Capital divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Risk Based Capital as defined in the regulations.

+ References

+ Details

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

- Definition

The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

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

- Definition

The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958570-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=d3e65071-112826

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

+ References

+ Details

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

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=smbk_SmartfinancialIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=smbk_SmartBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: