Financing Receivable, Loan to Value Ratio of Appraised Value of Property

No definition available.

Name:	acnb_FinancingReceivableLoantoValueRatioofAppraisedValueofProperty
Namespace Prefix:	acnb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Loan to Value Ratio of Appraised Value of Property, Required to have Private Mortgage Insurance if in excess of this percentage.

+ References

No definition available.

+ Details

Name:	acnb_FinancingReceivableLoantoValueRatioofAppraisedValueofPropertyRequiredtohavePrivateMortgageInsurance
Namespace Prefix:	acnb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Modifications, Number of Contracts Paid Off

+ References

No definition available.

+ Details

Name:	acnb_FinancingReceivableModificationsNumberofContractsPaidOff
Namespace Prefix:	acnb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Modifications, Subsequent Default, Number of Contracts with Active Forbearance Agreements

+ References

No definition available.

+ Details

Name:	acnb_FinancingReceivableModificationsSubsequentDefaultNumberofContractswithActiveForbearanceAgreements
Namespace Prefix:	acnb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable Modifications Subsequent Default Periodic Late Payments

+ References

No definition available.

+ Details

Name:	acnb_FinancingReceivableModificationsSubsequentDefaultPeriodicLatePayments
Namespace Prefix:	acnb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Number of Applications Awarded

+ References

No definition available.

+ Details

Name:	acnb_FinancingReceivableNumberofApplicationsAwarded
Namespace Prefix:	acnb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable, Projected Fee Income

+ References

No definition available.

+ Details

Name:	acnb_FinancingReceivableProjectedFeeIncome
Namespace Prefix:	acnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Financing Receivable, Term

+ References

No definition available.

+ Details

Name:	acnb_FinancingReceivableTerm
Namespace Prefix:	acnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Total Amount Awarded

+ References

No definition available.

+ Details

Name:	acnb_FinancingReceivableTotalAmountAwarded
Namespace Prefix:	acnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of Maximum Days of Loan Being Classified as Impaired for Corporation to Order Third Party Valuation

+ References

No definition available.

+ Details

Name:	acnb_NumberofMaximumDaysofLoanBeingClassifiedasImpairedforCorporationtoOrderThirdPartyValuation
Namespace Prefix:	acnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Minimum Months for Corporation to Order Updated Valuation

+ References

No definition available.

+ Details

Name:	acnb_NumberofMinimumMonthsforCorporationtoOrderUpdatedValuation
Namespace Prefix:	acnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Previous Months with No Updated Valuation Completed for Corporation to Update Valuation

+ References

No definition available.

+ Details

Name:	acnb_NumberofPreviousMonthswithNoUpdatedValuationCompletedforCorporationtoUpdateValuation
Namespace Prefix:	acnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Threshold Period Past Due for Corporation to Order Updated Valuation on Financing Receivable

+ References

No definition available.

+ Details

Name:	acnb_ThresholdPeriodPastDueforCorporationtoOrderUpdatedValuationonFinancingReceivable
Namespace Prefix:	acnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Threshold Period Past Due to Discontinue Accrual Interest on Financing Receivable

+ References

No definition available.

+ Details

Name:	acnb_ThresholdPeriodPastDuetoDiscontinueAccrualInterestonFinancingReceivable
Namespace Prefix:	acnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

+ Details

Name:	us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Threshold period for when financing receivable is considered past due to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919253-210447

+ Details

Name:	us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.1)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

Name:	us-gaap_InterestAndFeeIncomeLoansAndLeases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL49126937-111524

+ Details

Name:	us-gaap_MortgageLoansInProcessOfForeclosureAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Cash received from principal payments made on loans related to operating activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585

+ Details

Name:	us-gaap_ProceedsFromLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=acnb_ResidentialMortgageandCommercialLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=acnb_CARESActMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationNameAxis=us-gaap_EntityLoanModificationProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=acnb_HomeEquityLinesOfCreditPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=acnb_NonaccrualMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=acnb_AccrualMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans - Narrative (Details)	3 Months Ended		6 Months Ended		12 Months Ended
Loans - Narrative (Details)	Jun. 30, 2020 USD ($) application	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) Contract application loan	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for order of valuations (at least)			18 months
Troubled debt restructured loans, balance	$ 3,892,000	$ 4,061,000	$ 3,892,000	$ 4,061,000
Number of troubled debt restructured loan paid off \| Contract					1
Number of loans which has periodic late payments \| Contract			1
Financing Receivable, Modifications, Subsequent Default, Number of Contracts with Active Forbearance Agreements			0
Consumer mortgage loans secured by residential real estate properties for which formal foreclosure proceedings are in process	763,000		$ 763,000		$ 822,000
Recognized loan fee income	$ 20,180,000	16,038,000	$ 39,215,000	31,706,000
Residential mortgage and commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due to discontinue accrual interest on financing receivable			90 days
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due for write-off of financing receivable (no later than)	120 days		120 days
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period of financing receivable, updated valuation on real estate secured loans (number of days past due)			90 days
Number of previous months with no updated valuation completed for corporation to update valuation			12 months
Impaired financing receivable, valuation on real estate collateralized loans (number of days after the loan is classified as impaired)			30 days
CARES Act
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructured loans, balance	$ 234,636,342		$ 234,636,342
Number of loans with temporary modifications \| loan			466
Number of applications \| application	1,382		1,382
Total amount under PPP (up to)	$ 158,989,693		$ 158,989,693
Projected fee income			6,000,000
Recognized loan fee income	677,000
CARES Act \| Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructured loans, balance	12,605,748		$ 12,605,748
Number of loans with temporary modifications \| loan			119
Entity Loan Modification Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from paid off troubled debt restructured loans					$ 2,198,000
Maximum \| Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term			20 years
Loan-to-value ratio (no greater than)			80.00%
Maximum \| Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term			30 years
Loan-to-value ratio (no greater than)			80.00%
Loan-to-value ratio that requires private mortgage insurance (in excess of)			80.00%
Maximum \| Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term			20 years
Loan-to-value ratio (no greater than)			90.00%
Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructured loans, balance	159,000	228,000	$ 159,000	228,000
Accrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructured loans, balance	$ 3,733,000	$ 3,833,000	$ 3,733,000	$ 3,833,000