ACNB Corporation (Parent Company Only) Financial Information (Statements of Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Net income	$ 8,886	$ 8,502	$ 8,419
Net Cash Provided by Operating Activities	9,303	18,154	8,908
Net Cash Used in Investing Activities	(17,797)	(48,286)	(7,370)
Repayments on long-term debt	21,237	10,308	20,795
Proceeds from issuance of common stock	295	257
Dividends paid	(4,524)	(4,512)	(4,506)
Net Cash Used in Financing Activities	37,256	28,582	(1,503)
Net Increase (Decrease) in Cash and Cash Equivalents	28,762	(1,550)	35
CASH AND CASH EQUIVALENTS - BEGINNING	22,623	24,173	24,138
CASH AND CASH EQUIVALENTS - ENDING	51,385	22,623	24,173
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	8,886	8,502	8,419
Equity in undistributed earnings of subsidiaries	(3,935)	(3,551)	(3,437)
(Increase) Decrease in receivable from banking subsidiary	(261)	(350)	21
Other	671	45	257
Net Cash Provided by Operating Activities	5,361	4,646	5,260
Repayments on long-term debt	(237)	(308)	(795)
Proceeds from issuance of common stock	295	257
Dividends paid	(4,524)	(4,512)	(4,506)
Net Cash Used in Financing Activities	(4,466)	(4,563)	(5,301)
Net Increase (Decrease) in Cash and Cash Equivalents	895	83	(41)
CASH AND CASH EQUIVALENTS - BEGINNING	266	183	224
CASH AND CASH EQUIVALENTS - ENDING	$ 1,161	$ 266	$ 183