XML 14 R1.htm IDEA: XBRL DOCUMENT v3.22.0.1
Cover Page - USD ($)
 12 Months Ended
Dec. 31, 2021
Mar. 14, 2022
Jun. 30, 2021
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Document Transition Report false    
Entity File Number 1-35015    
Entity Registrant Name ACNB CORP    
Entity Incorporation, State or Country Code PA    
Entity Tax Identification Number 23-2233457    
Entity Address, Address Line One 16 Lincoln Square    
Entity Address, City or Town Gettysburg    
Entity Address, State or Province PA    
Entity Address, Postal Zip Code 17325    
City Area Code 717    
Local Phone Number 334-3161    
Title of 12(b) Security Common Stock, $2.50 par value per share    
Trading Symbol ACNB    
Security Exchange Name NASDAQ    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Public Float     $ 233,741,282
Entity Common Stock, Shares Outstanding   8,679,206  
Entity Central Index Key 0000715579    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus FY    
Amendment Flag false    
ICFR Auditor Attestation Flag false    
Auditor Firm ID 49    
Auditor Name RSM US LLP    
Auditor Location Philadelphia, Pennsylvania