ACNB CORPORATION (PARENT COMPANY ONLY) FINANCIAL INFORMATION (Statements of Condition) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
ASSETS
Cash	$ 13,468	$ 13,502
Investments in low-income housing partnerships	3,345	3,793
Securities and other assets	18,519	20,269
Total assets	1,147,925	1,089,808	$ 1,046,047
LIABILITIES AND STOCKHOLDERS’ EQUITY
Long-term debt	76,500	80,937
Other liabilities	8,528	8,274
Stockholders’ equity	114,715	110,022	$ 106,802	$ 101,264
Total Liabilities and Stockholders’ Equity	1,147,925	1,089,808
Parent Company [Member]
ASSETS
Cash	4,448	4,541
Investments in low-income housing partnerships	1,336	1,659
Securities and other assets	1,340	1,228
Receivable from banking subsidiary	2,769	2,638
Total assets	114,769	111,525
LIABILITIES AND STOCKHOLDERS’ EQUITY
Long-term debt	0	1,437
Other liabilities	54	66
Stockholders’ equity	114,715	110,022
Total Liabilities and Stockholders’ Equity	114,769	111,525
Banking Subsidiary [Member] | Parent Company [Member]
ASSETS
Investment	95,948	92,168
Other Subsidiary [Member] | Parent Company [Member]
ASSETS
Investment	$ 8,928	$ 9,291