Parent Company (Franklin Financial Services Corporation) Financial Information (Statements Of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net income	$ (7,263)	$ 3,076	$ 3,342	$ 3,020	$ 1,723	$ 2,075	$ 1,561	$ 2,726	$ 2,176	$ 8,087	$ 10,204
Adjustments to reconcile net income to net cash provided by operating activities:
Stock option compensation									161	88	74
Deferred tax benefit									(831)	(832)	(111)
Net cash provided by operating activities									16,252	14,856	13,290
Dividends paid									(4,031)	(3,523)	(3,139)
Cash received from option exercises									175	82	92
Common stock issued under dividend reinvestment plan									991	1,671	1,246
Treasury stock purchase										(795)
Net cash provided by financing activities									37,926	85,313	26,451
(Decrease) increase in cash and cash equivalents									21,938	(2,501)	(9,427)
Cash and cash equivalents as of January 1				36,665				39,166	36,665	39,166	48,593
Cash and cash equivalents as of December 31	58,603				36,665				58,603	36,665	39,166
Franklin Financial Services Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									2,176	8,087	10,204
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed loss (income) of subsidiary									(290)	4,752	10,391
Stock option compensation									161	88	74
Deferred tax benefit									(26)
(Increase) decrease in other assets/liabilities									(337)	(307)	1,800
Net cash provided by operating activities									2,264	3,116	1,687
Dividends paid									(4,031)	(3,523)	(3,139)
Cash received from option exercises									175	82	92
Common stock issued under dividend reinvestment plan									991	1,671	1,246
Treasury stock purchase										(795)
Net cash provided by financing activities									(2,865)	(2,565)	(1,801)
(Decrease) increase in cash and cash equivalents									(601)	551	(114)
Cash and cash equivalents as of January 1				$ 851				$ 300	851	300	414
Cash and cash equivalents as of December 31	$ 250				$ 851				$ 250	$ 851	$ 300