Basis of Presentation and Nature of Operations	3 Months Ended
Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	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 Russell Insurance Group, Inc. (RIG). The Bank engages in full-service commercial and consumer banking and trust services through its twenty-two retail banking office locations in Adams, Cumberland, Franklin and York Counties, Pennsylvania. There is also a loan production office situated in York County, Pennsylvania. 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 month period ended March 31, 2017, are not necessarily indicative of the results to be expected for the full year. Fixed assets held for sale is measured at the lower of its carrying amount or fair value less cost to sell. On November 22, 2016, ACNB announced the execution of the Agreement and Plan of Reorganization effective November 21, 2016, whereby New Windsor Bancorp, Inc. (“New Windsor”) will be merged with and into an ACNB acquisition subsidiary and, as soon as possible thereafter, New Windsor State Bank, New Windsor’s wholly-owned subsidiary bank, will merge with and into ACNB Bank. Two directors from New Windsor will join the boards of ACNB and ACNB Bank, respectively, and ACNB Bank will operate in the Maryland market as “NWSB Bank, a division of ACNB Bank”. Based on the financial results as of March 31, 2017, the combined company will have pro forma total assets of $1.51 billion, total deposits of $1.25 billion, and loans of $1.15 billion. The boards of directors of both ACNB and New Windsor have unanimously approved the transaction. Completion of the transaction is subject to customary closing conditions, including regulatory approvals and the approval of stockholders of New Windsor. The transaction is expected to close in either late second or early third quarter of 2017. During the three months ended March 31, 2017, merger related expenses of $162,000 were incurred for this proposed purchase. During the year ended December 31, 2016, merger related expenses of $472,000 were incurred for this proposed purchase. The Corporation has evaluated events and transactions occurring subsequent to the statement of condition date of March 31, 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, provides banking, insurance, and financial services to businesses and consumers through its wholly-owned subsidiaries, ACNB Bank (Bank) and Russell Insurance Group, Inc. (RIG). The Bank engages in full-service commercial and consumer banking and trust services through its twenty-two retail banking office locations in Adams, Cumberland, Franklin and York Counties, Pennsylvania. There is also a loan production office situated in York County, Pennsylvania.

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 month period ended March 31, 2017, are not necessarily indicative of the results to be expected for the full year. Fixed assets held for sale is measured at the lower of its carrying amount or fair value less cost to sell.

On November 22, 2016, ACNB announced the execution of the Agreement and Plan of Reorganization effective November 21, 2016, whereby New Windsor Bancorp, Inc. (“New Windsor”) will be merged with and into an ACNB acquisition subsidiary and, as soon as possible thereafter, New Windsor State Bank, New Windsor’s wholly-owned subsidiary bank, will merge with and into ACNB Bank. Two directors from New Windsor will join the boards of ACNB and ACNB Bank, respectively, and ACNB Bank will operate in the Maryland market as “NWSB Bank, a division of ACNB Bank”. Based on the financial results as of March 31, 2017, the combined company will have pro forma total assets of $1.51 billion, total deposits of $1.25 billion, and loans of $1.15 billion. The boards of directors of both ACNB and New Windsor have unanimously approved the transaction. Completion of the transaction is subject to customary closing conditions, including regulatory approvals and the approval of stockholders of New Windsor. The transaction is expected to close in either late second or early third quarter of 2017. During the three months ended March 31, 2017, merger related expenses of $162,000 were incurred for this proposed purchase. During the year ended December 31, 2016, merger related expenses of $472,000 were incurred for this proposed purchase.

The Corporation has evaluated events and transactions occurring subsequent to the statement of condition date of March 31, 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.