ACNB CORPORATION (PARENT COMPANY ONLY) FINANCIAL INFORMATION (Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Other income									$ 12,406	$ 11,904	$ 11,703
Income tax benefit									(3,761)	(3,080)	(2,535)
Net Income	$ 2,852	$ 2,812	$ 2,810	$ 2,543	$ 2,463	$ 2,624	$ 2,731	$ 2,472	11,017	10,290	9,315
Comprehensive Income									9,014	7,461	9,633
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Investment Income, Dividend									4,820	4,801	4,781
Other income									190	310	34
Total Revenues									5,010	5,111	4,815
Expenses									431	697	817
Net income before taxes and equity in undistributed earnings of subsidiaries									4,579	4,414	3,998
Income tax benefit									381	810	944
Net income before equity in undistributed earnings of subsidiaries									4,960	5,224	4,942
Equity in undistributed earnings of subsidiaries									6,057	5,066	4,373
Net Income									11,017	10,290	9,315
Comprehensive Income									$ 9,014	$ 7,461	$ 9,633