Regulatory Capital Matters (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Common equity tier 1 capital ratio
Actual, Amount	$ 203,287	$ 199,201
Actual, Ratio	12.06%	11.86%
Requirement for Capital Adequacy Purposes, Amount	$ 75,848	$ 75,573
Requirement for Capital Adequacy Purposes, Ratio	4.50%	4.50%
Total risk based capital ratio
Actual, Amount	$ 218,058	$ 213,725
Actual, Ratio	12.94%	12.73%
Requirement for Capital Adequacy Purposes, Amount	$ 134,841	$ 134,352
Requirement for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Tier 1 risk based capital ratio
Actual, Amount	$ 205,508	$ 201,410
Actual, Ratio	12.19%	11.99%
Requirement for Capital Adequacy Purposes, Amount	$ 101,131	$ 100,764
Requirement for Capital Adequacy Purposes, Ratio	6.00%	6.00%
Tier 1 leverage ratio
Actual, Amount	$ 205,508	$ 201,410
Actual, Ratio	9.68%	9.50%
Requirement for Capital Adequacy Purposes, Amount	$ 84,894	$ 84,800
Requirement for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Farmers National Banc Corp
Common equity tier 1 capital ratio
Actual, Amount	$ 190,895	$ 192,080
Actual, Ratio	11.29%	11.45%
Requirement for Capital Adequacy Purposes, Amount	$ 76,064	$ 75,462
Requirement for Capital Adequacy Purposes, Ratio	4.50%	4.50%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 109,870	$ 109,001
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Total risk based capital ratio
Actual, Amount	$ 203,445	$ 204,395
Actual, Ratio	12.04%	12.19%
Requirement for Capital Adequacy Purposes, Amount	$ 135,225	$ 134,155
Requirement for Capital Adequacy Purposes, Ratio	8.00%	8.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 169,031	$ 167,694
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 risk based capital ratio
Actual, Amount	$ 190,895	$ 192,080
Actual, Ratio	11.29%	11.45%
Requirement for Capital Adequacy Purposes, Amount	$ 101,419	$ 100,616
Requirement for Capital Adequacy Purposes, Ratio	6.00%	6.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 135,225	$ 134,155
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Tier 1 leverage ratio
Actual, Amount	$ 190,895	$ 192,080
Actual, Ratio	9.05%	9.12%
Requirement for Capital Adequacy Purposes, Amount	$ 84,359	$ 84,253
Requirement for Capital Adequacy Purposes, Ratio	4.00%	4.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 105,448	$ 105,316
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%

Tier one common capital.

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Tier one common capital ratio.

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Tier one common capital ratio

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Tier one common capital required for capital adequacy.

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Tier one risk based common capital required for capital adequacy to risk weighted assets.

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Tier one risk based common capital required to be well capitalized.

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Tier one common capital required to be well capitalized to risk weighted assets.

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The amount of total capital as defined in the regulations.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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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.

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

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-Name Accounting Standards Codification
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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.

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

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

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

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

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

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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.

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

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Tier 1 Risk Based Capital as defined in the regulations.

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

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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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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.

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

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