Basis of Presentation and Nature of Operations (Details) - bank			9 Months Ended
	Jan. 11, 2020	Jul. 01, 2017	Sep. 30, 2021
Business Acquisition [Line Items]
Number of community banking office locations, ACNB			31
Adams, Cumberland, Franklin and York Counties, Pennsylvania
Business Acquisition [Line Items]
Number of community banking office locations, ACNB			20
Carroll and Frederick Counties, Maryland
Business Acquisition [Line Items]
Number of community banking office locations, ACNB			11
New Windsor
Business Acquisition [Line Items]
Number of community banking offices acquired		6
Frederick County Bancorp, Inc.
Business Acquisition [Line Items]
Number of community banking offices acquired	5