Basis of Presentation and Nature of Operations (Details)	3 Months Ended
Mar. 31, 2018 bank
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of community banking office locations, ACNB	22
Number of community banking office locations, NWSB	7

Number of Full-service Bank Offices attributable to the Parent Company.

No definition available.

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