Acquisition and Divestiture Activity - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended
	Mar. 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Northern Indiana [Member] Store	Jun. 30, 2013 Southwest Michigan [Member] Store	Sep. 15, 2012 Indiana Community Bancorp [Member] Store	Jun. 30, 2013 Indiana Community Bancorp [Member]	Jun. 30, 2013 Bank Of America [Member] Store
Loans At Acquisition Date [Line Items]
Percentage of interest acquired						100.00%
Number of branch locations				4	20	17		24
Number of shares issued in acquisition						6.6
Value of shares issued in acquisition						$ 88,500,000
Net tangible assets acquired							(732,000)
Definite-lived intangible assets acquired							3,024,000
Deposits held for sale			150,000,000
Number of banking center to be consolidated			19
Gain on sale of banking centers			150,100,000
Deposit premium	2,200,000
Deposits to be included in transaction		575,000,000
Loan balances to be included in transaction		$ 5,000,000
Percentage of deposit premium								2.94%