Subordinated Debentures - Additional Information (Detail) - USD ($)	1 Months Ended				12 Months Ended
	Dec. 31, 2006	Oct. 31, 2004	Jun. 30, 2004	Mar. 31, 2004	Dec. 31, 2015	Dec. 31, 2014
Subordinate Debenture [Line Items]
LIBOR period					3 months
Carrying value of securities, net of remaining purchase discount					$ 32,797,000	$ 32,642,000
Horizon Statutory Trust Two [Member]
Subordinate Debenture [Line Items]
Trust Preferred Capital Securities Sold		$ 10,300,000
Securities bearing interest rate					90-day LIBOR plus 1.95%
Junior subordinated debentures and the securities variable rate		1.95%
LIBOR period					90 days
Interest rate on junior subordinated debentures and securities					2.56%
Junior subordinated debentures maturity date					Oct. 21, 2034
Cost of issuance of the securities		$ 17,500
First call date of the securities					Oct. 31, 2009
Horizon Bancorp Capital Trust Three [Member]
Subordinate Debenture [Line Items]
Trust Preferred Capital Securities Sold	$ 12,400,000
Securities bearing interest rate					90-day LIBOR plus 1.65%
Junior subordinated debentures and the securities variable rate	1.65%
LIBOR period					90 days
Interest rate on junior subordinated debentures and securities					2.26%
Junior subordinated debentures maturity date					Jan. 30, 2037
Cost of issuance of the securities	$ 12,647
Alliance Financial Statutory Trust One [Member]
Subordinate Debenture [Line Items]
Trust Preferred Capital Securities Sold			$ 5,200,000
Securities bearing interest rate					90-day LIBOR plus 2.65%
Junior subordinated debentures and the securities variable rate			2.65%
LIBOR period					90 days
Interest rate on junior subordinated debentures and securities					3.26%
Junior subordinated debentures maturity date					Jun. 01, 2034
Am Tru Statutory Trust One [Member]
Subordinate Debenture [Line Items]
Trust Preferred Capital Securities Sold				$ 3,500,000
Securities bearing interest rate					90-day LIBOR plus 2.85%
Junior subordinated debentures and the securities variable rate				2.85%
LIBOR period					90 days
Interest rate on junior subordinated debentures and securities					3.46%
Junior subordinated debentures maturity date					Mar. 01, 2034
Carrying value of securities, net of remaining purchase discount					$ 3,100,000
Heartland Statutory Trust Two [Member]
Subordinate Debenture [Line Items]
Trust Preferred Capital Securities Sold	$ 3,000,000
Securities bearing interest rate					90-day LIBOR plus 1.67%
Junior subordinated debentures and the securities variable rate	1.67%
LIBOR period					90 days
Interest rate on junior subordinated debentures and securities					2.28%
Junior subordinated debentures maturity date					Dec. 01, 2036
Carrying value of securities, net of remaining purchase discount					$ 1,700,000