Basis of Presentation and Nature of Operations	9 Months Ended
Sep. 30, 2017
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, is the financial holding company for the wholly-owned subsidiaries of ACNB Bank, Gettysburg, Pennsylvania, and Russell Insurance Group, Inc. (RIG), Westminster, Maryland. ACNB Bank serves its marketplace with banking and trust services via a network of twenty-two retail banking offices located in the four southcentral Pennsylvania counties of Adams, Cumberland, Franklin and York. There is also a loan production office situated in York County, Pennsylvania. On July 1, 2017, ACNB completed its previously announced acquisition of New Windsor Bancorp, Inc. (“NW Bancorp”) of Taneytown, Maryland. At the effective time of the merger, NW Bancorp 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 Maryland market as “NWSB Bank, A Division of ACNB Bank”. NWSB Bank, a division of ACNB Bank, serves its marketplace with banking and investment services via a network of seven retail banking offices located in Carroll County, Maryland. RIG is a full-service insurance agency based in Westminster, Maryland, with a second location in Germantown, Maryland. The agency offers a broad range of property and casualty, life, and health insurance to both commercial and individual clients. The Corporation’s primary source of revenue is 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 (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 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 2016 ACNB Corporation Annual Report on Form 10-K, filed with the SEC on March 15, 2017. 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 and nine month periods ended September 30, 2017, 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 statement of condition date of September 30, 2017, 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.

Basis of Presentation and Nature of Operations

ACNB Corporation (the Corporation or ACNB), headquartered in Gettysburg, Pennsylvania, is the financial holding company for the wholly-owned subsidiaries of ACNB Bank, Gettysburg, Pennsylvania, and Russell Insurance Group, Inc. (RIG), Westminster, Maryland. ACNB Bank serves its marketplace with banking and trust services via a network of twenty-two retail banking offices located in the four southcentral Pennsylvania counties of Adams, Cumberland, Franklin and York. There is also a loan production office situated in York County, Pennsylvania.

On July 1, 2017, ACNB completed its previously announced acquisition of New Windsor Bancorp, Inc. (“NW Bancorp”) of Taneytown, Maryland. At the effective time of the merger, NW Bancorp 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 Maryland market as “NWSB Bank, A Division of ACNB Bank”. NWSB Bank, a division of ACNB Bank, serves its marketplace with banking and investment services via a network of seven retail banking offices located in Carroll County, Maryland.

RIG is a full-service insurance agency based in Westminster, Maryland, with a second location in Germantown, Maryland. The agency offers a broad range of property and casualty, life, and health insurance to both commercial and individual clients.

The Corporation’s primary source of revenue is 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 (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 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 2016 ACNB Corporation Annual Report on Form 10-K, filed with the SEC on March 15, 2017. 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 and nine month periods ended September 30, 2017, 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 statement of condition date of September 30, 2017, 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.