Regulatory Matters (Schedule Of The Total Risk-based, Tier 1 Risk-based And Tier 1 Leverage Requirements) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Franklin Financial Services Corporation [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Risk-based Capital Ratio: Ratio	14.06%	14.41%	[1]
Common Equity Tier 1 Risk-based Capital Ratio: Adequately Capitalized Minimum: Ratio	4.50%	4.50%	[1]
Tier 1 Risk-based Capital Ratio: Ratio	14.06%	14.41%	[2]
Tier 1 Risk-based Capital Ratio: Adequately Capitalized Minimum: Ratio	6.00%	6.00%	[2]
Total Risk-based Capital Ratio: Ratio	15.31%	15.67%	[3]
Total Risk-based Capital Ratio: Adequately Capitalized Minimum: Ratio	8.00%	8.00%	[3]
Tier 1 Leverage Ratio: Ratio	9.73%	10.11%	[4]
Tier 1 Leverage Ratio: Adequately Capitalized Minimum: Ratio	4.00%	4.00%	[4]
Common Equity Tier 1 Risk-based Capital Ratio: Amount	$ 112,315	$ 111,691	[1]
Common Equity Tier 1 Risk-based Capital Ratio: Adequately Capitalized Minimum, Amount	35,953	34,889	[1]
Tier 1 Risk-based Capital Ratio: Amount	112,315	111,691	[2]
Tier 1 Risk-based Capital Ratio: Minimum to be Adequately Capitalized Amount	47,938	46,518	[2]
Total Risk-based Capital Ratio: Amount	122,324	121,456	[3]
Total Risk-based Capital Ratio: Minimum to be Adequately Capitalized Amount	63,917	62,024	[3]
Tier 1 Leverage Ratio: Amount	112,315	111,691	[4]
Tier 1 Leverage Ratio: Minimum to be Adequately Capitalized Amount	$ 46,175	$ 44,209	[4]
Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Risk-based Capital Ratio: Ratio	13.93%	14.29%	[1]
Common Equity Tier 1 Risk-based Capital Ratio: Adequately Capitalized Minimum: Ratio	4.50%	4.50%	[1]
Common Equity Tier 1 Risk-based Capital Ratio: Well Capitalized Minimum: Ratio	6.50%	6.50%	[1]
Tier 1 Risk-based Capital Ratio: Ratio	13.93%	14.29%	[2]
Tier 1 Risk-based Capital Ratio: Adequately Capitalized Minimum: Ratio	6.00%	6.00%	[2]
Tier 1 Risk-based Capital Ratio: Well Capitalized Minimum: Ratio	8.00%	8.00%	[2]
Total Risk-based Capital Ratio: Ratio	15.19%	15.55%	[3]
Total Risk-based Capital Ratio: Adequately Capitalized Minimum: Ratio	8.00%	8.00%	[3]
Total Risk-based Capital Ratio: Well Capitalized Minimum: Ratio	10.00%	10.00%	[3]
Tier 1 Leverage Ratio: Ratio	9.64%	10.02%	[4]
Tier 1 Leverage Ratio: Adequately Capitalized Minimum: Ratio	4.00%	4.00%	[4]
Tier 1 Leverage Ratio: Well Capitalized Minimum: Ratio	5.00%	5.00%	[4]
Common Equity Tier 1 Risk-based Capital Ratio: Amount	$ 111,496	$ 110,932	[1]
Common Equity Tier 1 Risk-based Capital Ratio: Adequately Capitalized Minimum, Amount	36,010	34,943	[1]
Common Equity Tier 1 Risk-based Capital Ratio: Well Capitalized Minimum, Amount	52,014	50,473	[1]
Tier 1 Risk-based Capital Ratio: Amount	111,496	110,932	[2]
Tier 1 Risk-based Capital Ratio: Minimum to be Adequately Capitalized Amount	48,013	46,590	[2]
Tier 1 Risk-based Capital Ratio: Minimum to be Well Capitalized Amount	64,018	62,121	[2]
Total Risk-based Capital Ratio: Amount	121,521	120,712	[3]
Total Risk-based Capital Ratio: Minimum to be Adequately Capitalized Amount	64,018	62,121	[3]
Total Risk-based Capital Ratio: Minimum to be Well Capitalized Amount	80,022	77,651	[3]
Tier 1 Leverage Ratio: Amount	111,496	110,932	[4]
Tier 1 Leverage Ratio: Minimum to be Adequately Capitalized Amount	46,242	44,270	[4]
Tier 1 Leverage Ratio: Minimum to be Well Capitalized Amount	$ 57,802	$ 55,337	[4]

[1] Common equity Tier 1 capital / total risk-weighted assets

[2] Tier 1 capital / total risk-weighted assets

[3] Total risk-based capital / total risk-weighted assets

[4] Tier 1 capital / average quarterly assets