Parent Company (Franklin Financial Services Corporation) Financial Information (Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 58,603	$ 36,665	$ 39,166	$ 48,593
Other assets	6,930	5,506
Total assets	1,179,813	1,127,443
Other Liabilities	17,488	4,560
Total liabilities	1,064,669	1,010,950
Shareholders' equity	115,144	116,493	111,376	103,521
Total liabilities and shareholders' equity	1,179,813	1,127,443
Franklin Financial Services Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	250	851	$ 300	$ 414
Investment securities	365
Equity investment in subsidiaries	114,387	115,794
Other assets	184	39
Total assets	115,186	116,684
Other Liabilities	42	191
Total liabilities	42	191
Shareholders' equity	115,144	116,493
Total liabilities and shareholders' equity	$ 115,186	$ 116,684