Parent Company (Franklin Financial Services Corporation) Financial Information (Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 57,146	$ 83,828	$ 52,957
Other assets	12,909	7,852
Total assets	1,535,038	1,269,157
Other Liabilities	10,402	11,076
Total liabilities	1,389,862	1,141,629
Shareholders' equity	145,176	127,528	118,396
Total liabilities and shareholders' equity	1,535,038	1,269,157
Franklin Financial Services Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	20,109	164	$ 108
Investment securities	391	440
Equity investment in subsidiaries	142,949	126,069
Other assets	1,282	859
Total assets	164,731	127,532
Other Liabilities	19,555	4
Total liabilities	19,555	4
Shareholders' equity	145,176	127,528
Total liabilities and shareholders' equity	$ 164,731	$ 127,532