Acquisition and Divestiture Activity - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended		0 Months Ended			9 Months Ended		0 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended		1 Months Ended
	Sep. 05, 2013 Store	Mar. 31, 2013	Sep. 30, 2013 Center	Dec. 31, 2013 Scenario, Forecast [Member] Center	Mar. 31, 2013 Southern Illinois And Western Kentucky [Member] Store	Jul. 12, 2013 Northern Indiana [Member] Store	Jul. 12, 2013 Southwest Michigan [Member] Store	Sep. 15, 2012 Indiana Community Bancorp [Member] Store	Sep. 30, 2013 Indiana Community Bancorp [Member]	Sep. 30, 2013 Indiana Community Bancorp [Member] Core Deposit [Member]	Jul. 12, 2013 Bank of America [Member] Store	Sep. 30, 2013 Bank of America [Member]	Sep. 30, 2013 Bank of America [Member] Community Banking [Member] Store	Sep. 30, 2013 Bank of America [Member] Community Banking [Member] Store	Sep. 30, 2013 Bank of America [Member] Community Banking [Member] Core Deposit [Member]	Sep. 30, 2013 Tower Financial Corporation [Member] Store	Sep. 10, 2013 Tower Financial Corporation [Member]	Sep. 05, 2013 Tower Financial Corporation [Member]
Loans at Acquisition Date [Line Items]
Percentage of interest acquired								100.00%
Number of branch locations	3				9	4	20	17			24		24	24		7
Number of shares issued in acquisition								6.6
Value of shares issued in acquisition								$ 88,500,000										$ 107,700,000
Net tangible assets acquired									(732,000)			16,097,000
Definite-lived intangible assets acquired									3,024,000	1,300,000					3,500,000
Percentage of deposit premium												2.94%
Estimated useful life of acquired identifiable intangible assets										7 years					7 years
Assets under management																702,000,000
Additional assets under management																719,000,000
Portion of share received by merged entity																	1.20
Consideration received in cash by merged entity																	$ 6.75
Deposits held for sale		150,000,000
Deposit premium		2,200,000
Deposits to be included in transaction	$ 31,000,000
Number of banking center to be consolidated			40	4