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Basis of Presentation and Nature of Operations (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023 USD ($) bank	Mar. 31, 2022 USD ($)	Jan. 01, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Business Acquisition [Line Items]
Number of community banking office locations, ACNB | bank					26
Allowance for credit losses on loans					$ 19,485	$ 18,963	$ (17,861)	$ 17,861	$ 19,033
Allowance for unfunded commitments					2,011		92	92
Forecast
Business Acquisition [Line Items]
Forecasted Unemployment Rates	5.10%	4.70%	4.30%	3.90%
Unfunded Loan Commitment
Business Acquisition [Line Items]
Allowance for credit losses on loans					2,000
Provision for Credit Losses					276	0
Financing Receivable Excluding Unfunded Commitments
Business Acquisition [Line Items]
Allowance for credit losses on loans					19,500
Provision for Credit Losses					97	$ 0
Revision of Prior Period, Adjustment
Business Acquisition [Line Items]
Adjustment							3,300
Allowance for credit losses on loans							(1,618)
Allowance for unfunded commitments							$ 1,643
Cumulative Effect, Period of Adoption, Adjustment
Business Acquisition [Line Items]
Allowance for credit losses on loans					1,600			$ 1,618
Cumulative Effect, Period of Adoption, Adjustment | Financing Receivable Excluding Unfunded Commitments
Business Acquisition [Line Items]
Allowance for credit losses on loans					$ (1,600)
Adams, Cumberland, Franklin and York Counties, Pennsylvania
Business Acquisition [Line Items]
Number of community banking office locations, ACNB | bank					17
Carroll and Frederick Counties, Maryland
Business Acquisition [Line Items]
Number of community banking office locations, ACNB | bank					9

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