Parent Company (Franklin Financial Services Corporation) Financial Information (Statements Of Comprehensive Income) (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
Securities:
Unrealized gains arising during the period	[1]									177	(1,176)	(498)
Reclassification adjustment for net (gains) losses included in net income	[1]									(3)	18	(716)
Net unrealized gains (losses)	[1]									174	(1,158)	(1,214)
Tax effect	[1]									(60)	394	413
Net of tax amount	[1]									114	(764)	(801)
Total other comprehensive loss										(821)	(493)	(622)
Franklin Financial Services Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Net income										2,176	8,087	10,204
Securities:
Unrealized gains arising during the period										201
Reclassification adjustment for net (gains) losses included in net income
Net unrealized gains (losses)										201
Tax effect										(68)
Net of tax amount										133
Total other comprehensive loss										133
Other comprehensive (loss) income of subsidiaries										(954)	(493)	(622)
Total Comprehensive Income										$ 1,355	$ 7,594	$ 9,582

[1] Securities / securities (gains) losses and OTTI losses, net $1, ($6), and $243 for years ended December 31, 2017, 2016, and 2015, respectively.