Regulatory Capital Matters (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Common equity tier 1 capital ratio
Actual, Amount	$ 168,876	$ 165,451
Actual, Ratio	11.82%	11.59%
Requirement for Capital Adequacy Purposes, Amount	$ 64,298	$ 64,245
Requirement for Capital Adequacy Purposes, Ratio	4.50%	4.50%
Total risk based capital ratio
Actual, Amount	$ 180,431	$ 176,571
Actual, Ratio	12.63%	12.37%
Requirement for Capital Adequacy Purposes, Amount	$ 114,307	$ 114,214
Requirement for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Tier 1 risk based capital ratio
Actual, Amount	$ 170,999	$ 167,550
Actual, Ratio	11.97%	11.74%
Requirement for Capital Adequacy Purposes, Amount	$ 85,730	$ 85,660
Requirement for Capital Adequacy Purposes, Ratio	6.00%	6.00%
Tier 1 leverage ratio
Actual, Amount	$ 170,999	$ 167,550
Actual, Ratio	9.34%	9.21%
Requirement for Capital Adequacy Purposes, Amount	$ 74,039	$ 72,803
Requirement for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Farmers National Banc Corp
Common equity tier 1 capital ratio
Actual, Amount	$ 161,871	$ 157,396
Actual, Ratio	11.36%	11.08%
Requirement for Capital Adequacy Purposes, Amount	$ 64,103	$ 63,938
Requirement for Capital Adequacy Purposes, Ratio	4.50%	4.50%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 92,593	$ 92,354
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Total risk based capital ratio
Actual, Amount	$ 171,261	$ 166,374
Actual, Ratio	12.02%	11.71%
Requirement for Capital Adequacy Purposes, Amount	$ 113,961	$ 113,667
Requirement for Capital Adequacy Purposes, Ratio	8.00%	8.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 142,451	$ 142,084
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 risk based capital ratio
Actual, Amount	$ 161,871	$ 157,396
Actual, Ratio	11.36%	11.08%
Requirement for Capital Adequacy Purposes, Amount	$ 85,471	$ 85,250
Requirement for Capital Adequacy Purposes, Ratio	6.00%	6.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 113,961	$ 113,667
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Tier 1 leverage ratio
Actual, Amount	$ 161,871	$ 157,396
Actual, Ratio	8.82%	8.65%
Requirement for Capital Adequacy Purposes, Amount	$ 73,442	$ 72,770
Requirement for Capital Adequacy Purposes, Ratio	4.00%	4.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 91,802	$ 90,963
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%