Regulatory Capital Matters (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Common equity tier 1 capital ratio
Actual, Amount	$ 171,914	$ 165,451
Actual, Ratio	11.61%	11.59%
Requirement for Capital Adequacy Purposes, Amount	$ 66,639	$ 64,245
Requirement for Capital Adequacy Purposes, Ratio	4.50%	4.50%
Total risk based capital ratio
Actual, Amount	$ 183,822	$ 176,571
Actual, Ratio	12.41%	12.37%
Requirement for Capital Adequacy Purposes, Amount	$ 118,469	$ 114,214
Requirement for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Tier 1 risk based capital ratio
Actual, Amount	$ 174,050	$ 167,550
Actual, Ratio	11.75%	11.74%
Requirement for Capital Adequacy Purposes, Amount	$ 88,851	$ 85,660
Requirement for Capital Adequacy Purposes, Ratio	6.00%	6.00%
Tier 1 leverage ratio
Actual, Amount	$ 174,050	$ 167,550
Actual, Ratio	9.37%	9.21%
Requirement for Capital Adequacy Purposes, Amount	$ 74,296	$ 72,803
Requirement for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Farmers National Banc Corp
Common equity tier 1 capital ratio
Actual, Amount	$ 163,392	$ 157,396
Actual, Ratio	11.06%	11.08%
Requirement for Capital Adequacy Purposes, Amount	$ 66,473	$ 63,938
Requirement for Capital Adequacy Purposes, Ratio	4.50%	4.50%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 96,017	$ 92,354
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Total risk based capital ratio
Actual, Amount	$ 173,112	$ 166,374
Actual, Ratio	11.72%	11.71%
Requirement for Capital Adequacy Purposes, Amount	$ 118,175	$ 113,667
Requirement for Capital Adequacy Purposes, Ratio	8.00%	8.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 147,719	$ 142,084
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 risk based capital ratio
Actual, Amount	$ 163,392	$ 157,396
Actual, Ratio	11.06%	11.08%
Requirement for Capital Adequacy Purposes, Amount	$ 88,631	$ 85,250
Requirement for Capital Adequacy Purposes, Ratio	6.00%	6.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 118,175	$ 113,667
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Tier 1 leverage ratio
Actual, Amount	$ 163,392	$ 157,396
Actual, Ratio	8.85%	8.65%
Requirement for Capital Adequacy Purposes, Amount	$ 73,840	$ 72,770
Requirement for Capital Adequacy Purposes, Ratio	4.00%	4.00%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 92,300	$ 90,963
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%