ACNB CORPORATION (PARENT COMPANY ONLY) FINANCIAL INFORMATION (Statements of Cash Flows) (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
CASH FLOWS FROM OPERATING ACTIVITIES
NET INCOME	$ 2,852	$ 2,812	$ 2,810	$ 2,543	$ 2,463	$ 2,624	$ 2,731	$ 2,472	$ 11,017	$ 10,290	$ 9,315
Net Cash Provided by Operating Activities									14,379	10,815	17,986
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of low-income housing partnerships									0	229	476
Net Cash Used in Investing Activities									(64,144)	(44,131)	(38,125)
CASH FLOWS USED IN FINANCING ACTIVITIES
Repayments on long-term borrowings									(22,437)	(29,266)	(14,251)
Proceeds from issuance of common stock									499	381	447
Dividends paid									(4,820)	(4,622)	(4,542)
Net Cash Provided by (Used in) Financing Activities									48,849	34,873	(13,130)
Net (Decrease) Increase in Cash and Cash Equivalents									(916)	1,557	(33,269)
CASH AND CASH EQUIVALENTS — BEGINNING				19,673				18,116	19,673	18,116	51,385
CASH AND CASH EQUIVALENTS — ENDING	18,757				19,673				18,757	19,673	18,116
Parent Company [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
NET INCOME									11,017	10,290	9,315
Equity in undistributed earnings of subsidiaries									(6,057)	(5,066)	(4,373)
Increase in receivable from banking subsidiary									(131)	(810)	(843)
Other									86	799	695
Net Cash Provided by Operating Activities									4,915	5,213	4,794
CASH FLOWS FROM INVESTING ACTIVITIES
Return of Investment from Subsidiary									750	250	1,500
Proceeds from sale of low-income housing partnerships									0	0	476
Net Cash Used in Investing Activities									750	250	1,976
CASH FLOWS USED IN FINANCING ACTIVITIES
Repayments on long-term borrowings									(1,437)	(266)	(251)
Proceeds from issuance of common stock									499	381	447
Dividends paid									(4,820)	(4,622)	(4,542)
Net Cash Provided by (Used in) Financing Activities									(5,758)	(4,507)	(4,346)
Net (Decrease) Increase in Cash and Cash Equivalents									(93)	956	2,424
CASH AND CASH EQUIVALENTS — BEGINNING				$ 4,541				$ 3,585	4,541	3,585	1,161
CASH AND CASH EQUIVALENTS — ENDING	$ 4,448				$ 4,541				$ 4,448	$ 4,541	$ 3,585