Capital Ratios (Narrative) (Details) - USD ($) $ in Billions	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital Ratios, Basel III, Capital Conservation Buffer, Year Three	2.50%
Community Bank Leverage Ratio, Minimum		9.00%
Paycheck Protection Program, Risk-Weight For Risk-Based Capital Rules	0.00%
Consolidated asset limit on small bank holding companies	$ 3
Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Risk-based Capital Ratio: Ratio	13.99%	14.62%
Tier One Leverage Capital to Average Assets	8.61%	9.59%
Common Equity Tier 1 Risk-based Capital Ratio: Well Capitalized Minimum: Ratio	6.50%
Tier 1 Risk-based Capital Ratio: Well Capitalized Minimum: Ratio	8.00%
Tier 1 Leverage Ratio: Well Capitalized Minimum: Ratio	5.00%
Total Risk-based Capital Ratio: Well Capitalized Minimum: Ratio	10.00%
Capital ratios, capital conservation buffer	7.25%
Total Risk-based Capital Ratio: Ratio	15.25%	15.87%

Capital Ratios, Basel III, Capital Conservation Buffer, Year Three

No definition available.

Name:	fraf_CapitalRatiosBaselIiiCapitalConservationBufferYearThree
Namespace Prefix:	fraf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Capital Ratios, Capital Conservation Buffer

+ References

No definition available.

+ Details

Name:	fraf_CapitalRatiosCapitalConservationBuffer
Namespace Prefix:	fraf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Community Bank Leverage Ratio, Minimum

+ References

No definition available.

+ Details

Name:	fraf_CommunityBankLeverageRatioMinimum
Namespace Prefix:	fraf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Consolidated Asset Limit On Small Bank Holding Companies

+ References

No definition available.

+ Details

Name:	fraf_ConsolidatedAssetLimitOnSmallBankHoldingCompanies
Namespace Prefix:	fraf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Paycheck Protection Program, Risk-Weight For Risk-Based Capital Rules

+ References

No definition available.

+ Details

Name:	fraf_PaycheckProtectionProgramRiskWeightForRiskBasedCapitalRules
Namespace Prefix:	fraf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Tangible Capital Required For Well Capitalized To Tangible Assets

+ References

No definition available.

+ Details

Name:	fraf_TangibleCapitalRequiredForWellCapitalizedToTangibleAssets
Namespace Prefix:	fraf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=d3e65071-112826

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Tangible Capital divided by Tangible assets as defined in the regulations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=d3e65071-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

+ Details

Name:	us-gaap_TangibleCapitalToTangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Leverage Capital divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: