Fair Value Measurements - Narrative (Details)	3 Months Ended
Mar. 31, 2018
Fair Value Disclosures [Abstract]
Period for order of valuations (at least)	18 months

Number of Minimum Months for Corporation to Order Updated Valuation

No definition available.

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