Parent Company Only Condensed Financial Information - Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income:
Dividends from subsidiaries									$ 543	$ 627	$ 652
Income tax benefit	$ (2,351)	$ (2,443)	$ (1,906)	$ (1,696)	$ (2,186)	$ (2,071)	$ (1,488)	$ (1,570)	(8,396)	(7,315)	(5,714)
NET INCOME	$ 11,357	$ 10,869	$ 11,011	$ 8,639	$ 9,675	$ 9,154	$ 8,543	$ 8,388	41,876	35,760	32,569
Farmers National Banc Corp
Income:
Interest and dividends on securities									12	15	8
Security gains/(losses)									(28)	41	(20)
TOTAL INCOME									31,930	36,787	10,602
Interest on borrowings									(361)	(154)	(133)
Other expenses									(2,746)	(2,352)	(2,087)
Income before income tax benefit and undistributed subsidiary income									28,823	34,281	8,382
Income tax benefit									592	470	450
Equity in undistributed net income of subsidiaries (dividends in excess of net income)									12,461	1,009	23,737
NET INCOME									41,876	35,760	32,569
Farmers National Banc Corp | Bank Segment
Income:
Dividends from subsidiaries									28,646	33,896	7,864
Equity in undistributed net income of subsidiaries (dividends in excess of net income)									12,244	508	23,687
Farmers National Banc Corp | Farmers Trust
Income:
Dividends from subsidiaries									2,300	2,300	1,900
Equity in undistributed net income of subsidiaries (dividends in excess of net income)									237	(31)	(20)
Farmers National Banc Corp | Captive Insurance
Income:
Dividends from subsidiaries									1,000	535	850
Equity in undistributed net income of subsidiaries (dividends in excess of net income)									$ (20)	$ 532	$ 70