Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Mar. 04, 2016	Jun. 30, 2015
Document and Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Entity Registrant Name	ACNB CORP
Entity Central Index Key	0000715579
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		6,039,724
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 122,345,128
Entity Voluntary Filers	No