Basis of Presentation and Nature of Operations	3 Months Ended
Basis of Presentation and Nature of Operations	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Nature of Operations	Basis of Presentation and Nature of Operations ACNB Corporation (the Corporation or ACNB), headquartered in Gettysburg, Pennsylvania, provides banking, insurance, and financial services to businesses and consumers through its wholly-owned subsidiaries, ACNB Bank (Bank) and ACNB Insurance Services, Inc., formerly Russell Insurance Group, Inc. The Bank engages in full-service commercial and consumer banking and wealth management services, including trust and retail brokerage, through its thirty-one community banking offices, including twenty community banking office locations in Adams, Cumberland, Franklin and York Counties, Pennsylvania, and eleven community banking office locations in Carroll and Frederick Counties, Maryland. There are also loan production offices situated in Lancaster and York, Pennsylvania, and Hunt Valley, Maryland. ACNB Insurance Services, Inc. is a full-service insurance agency based in Westminster, Maryland, with additional locations in Germantown and Jarrettsville, Maryland, and Gettysburg, Pennsylvania. The agency offers a broad range of property, casualty, health, life and disability insurance to both individual and commercial clients. On January 11, 2020, ACNB completed the acquisition of Frederick County Bancorp, Inc. (FCBI), a bank holding company based in Frederick, Maryland. In addition, Frederick County Bank, a Maryland state-chartered bank and FCBI’s wholly-owned subsidiary, merged with and into ACNB Bank. ACNB Bank now operates in the Frederick County, Maryland, market as “FCB Bank, A Division of ACNB Bank” and serves its marketplace with banking and wealth management services via the network of five community banking offices located in Frederick County, Maryland. On July 1, 2017, ACNB completed its acquisition of New Windsor Bancorp, Inc. (New Windsor) of Taneytown, Maryland. At the effective time of the acquisition, New Windsor merged with and into a wholly-owned subsidiary of ACNB, immediately followed by the merger of New Windsor State Bank (NWSB) with and into ACNB Bank. ACNB Bank now operates in the Carroll County, Maryland market as “NWSB Bank, A Division of ACNB Bank” and serves its marketplace with banking and wealth management services via the network of six community banking offices located in Carroll County, Maryland. The Corporation’s primary sources of revenue are interest income on loans and investment securities and fee income on its products and services. Expenses consist of interest expense on deposits and borrowed funds, provisions for loan losses, and other operating expenses. The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (US GAAP) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly ACNB Corporation’s financial position and the results of operations, comprehensive (loss) income, changes in stockholders’ equity, and cash flows. All such adjustments are of a normal recurring nature. The accounting policies followed by the Corporation are set forth in Note A to the Corporation’s consolidated financial statements in the 2021 ACNB Corporation Annual Report on Form 10-K, filed with the SEC on March 14, 2022. It is suggested that the consolidated financial statements contained herein be read in conjunction with the consolidated financial statements and notes included in the Corporation’s Annual Report on Form 10-K. The results of operations for the three month period ended March 31, 2022, are not necessarily indicative of the results to be expected for the full year. The Corporation has evaluated events and transactions occurring subsequent to the balance sheet date of March 31, 2022, for items that should potentially be recognized or disclosed in the consolidated financial statements. The evaluation was conducted through the date these consolidated financial statements were issued.