ACNB CORPORATION (PARENT COMPANY ONLY) FINANCIAL INFORMATION (Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Gain on sale of securities	$ 26	$ 0	$ 0	$ 0	$ 2	$ 158	$ 101	$ 0	$ 26	$ 261	$ 62
Other income									13,208	12,406	11,904
Income tax benefit									(3,768)	(3,761)	(3,080)
Net Income	$ 2,572	$ 2,768	$ 2,982	$ 2,547	$ 2,852	$ 2,812	$ 2,810	$ 2,543	10,869	11,017	10,290
Comprehensive Income									9,571	9,014	7,461
Parent Company
Condensed Financial Statements, Captions [Line Items]
Dividends from banking subsidiary									4,840	4,820	4,801
Gain on sale of securities									26	0	0
Other income									35	190	310
Total Revenues									4,901	5,010	5,111
Expenses									854	431	697
Net income before taxes and equity in undistributed earnings of subsidiaries									4,047	4,579	4,414
Income tax benefit									490	381	810
Net income before equity in undistributed earnings of subsidiaries									4,537	4,960	5,224
Equity in undistributed earnings of subsidiaries									6,332	6,057	5,066
Net Income									10,869	11,017	10,290
Comprehensive Income									$ 9,571	$ 9,014	$ 7,461