ACNB Corporation (Parent Company Only) Financial Information (Statements of Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Other income									$ 11,867	$ 11,737	$ 12,172
Income tax benefit									2,319	2,154	2,057
Net Income	2,218	2,304	2,128	2,236	1,756	2,180	2,106	2,460	8,886	8,502	8,419
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends from banking subsidiary									4,762	4,689	4,506
Other income									44	47	288
Total Revenues									4,806	4,736	4,794
Expenses									591	494	445
Net income before taxes and equity in undistributed earnings of subsidiaries									4,215	4,242	4,349
Income tax benefit									736	709	633
Net income before equity in undistributed earnings of subsidiaries									4,951	4,951	4,982
Equity in undistributed earnings of subsidiaries									3,935	3,551	3,437
Net Income									$ 8,886	$ 8,502	$ 8,419