Regulatory Capital Matters (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Common equity tier 1 capital ratio
Actual, Amount	$ 384,772	$ 362,950
Actual, Ratio	13.30%	13.16%
Requirement for Capital Adequacy Purposes, Amount	$ 130,199	$ 124,066
Requirement for Capital Adequacy Purposes, Ratio	4.50%	4.50%
Total risk based capital ratio
Actual, Amount	$ 505,226	$ 485,336
Actual, Ratio	0.1746	0.1760
Requirement for Capital Adequacy Purposes, Amount	$ 231,465	$ 220,562
Requirement for Capital Adequacy Purposes, Ratio	0.080	0.080
Tier 1 risk based capital ratio
Actual, Amount	$ 402,772	$ 380,950
Actual, Ratio	0.1392	0.1382
Requirement for Capital Adequacy Purposes, Amount	$ 173,599	$ 165,422
Requirement for Capital Adequacy Purposes, Ratio	0.060	0.060
Tier 1 leverage ratio
Actual, Amount	$ 402,772	$ 380,950
Actual, Ratio	0.0956	0.1012
Requirement for Capital Adequacy Purposes, Amount	$ 168,600	$ 150,629
Requirement for Capital Adequacy Purposes, Ratio	0.040	0.040
Farmers National Banc Corp
Common equity tier 1 capital ratio
Actual, Amount	$ 342,786	$ 345,065
Actual, Ratio	11.88%	12.55%
Requirement for Capital Adequacy Purposes, Amount	$ 129,843	$ 123,712
Requirement for Capital Adequacy Purposes, Ratio	4.50%	4.50%
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 187,551	$ 178,695
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Total risk based capital ratio
Actual, Amount	$ 370,240	$ 374,451
Actual, Ratio	0.1283	0.1362
Requirement for Capital Adequacy Purposes, Amount	$ 230,832	$ 219,933
Requirement for Capital Adequacy Purposes, Ratio	0.080	0.080
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 288,540	$ 274,916
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.100	0.100
Tier 1 risk based capital ratio
Actual, Amount	$ 342,786	$ 345,065
Actual, Ratio	0.1188	0.1255
Requirement for Capital Adequacy Purposes, Amount	$ 173,124	$ 164,950
Requirement for Capital Adequacy Purposes, Ratio	0.060	0.060
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 230,832	$ 219,933
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.080	0.080
Tier 1 leverage ratio
Actual, Amount	$ 342,786	$ 345,065
Actual, Ratio	0.0817	0.0919
Requirement for Capital Adequacy Purposes, Amount	$ 167,728	$ 150,217
Requirement for Capital Adequacy Purposes, Ratio	0.040	0.040
To be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 209,660	$ 187,772
To be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.050	0.050