Parent Company (Franklin Financial Services Corporation) Financial Information (Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Aug. 04, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 175,149	$ 57,146		$ 83,828
Other assets	12,652	12,909
Total assets	1,773,806	1,535,038
Subordinated notes	20,000		$ 20,000
Other liabilities	7,937	10,402
Total liabilities	1,616,741	1,389,862
Shareholders' equity	157,065	145,176		127,528
Total liabilities and shareholders' equity	1,773,806	1,535,038
Franklin Financial Services Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	17,637	20,109		$ 164
Investment securities	481	391
Equity investment in subsidiaries	157,620	142,949
Other assets	918	1,282
Total assets	176,656	164,731
Subordinated notes	19,588	19,555
Other liabilities	3
Total liabilities	19,591	19,555
Shareholders' equity	157,065	145,176
Total liabilities and shareholders' equity	$ 176,656	$ 164,731