Acquisition - Amounts of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	$ 1,081,419	$ 1,190,717
Carrying amount, net of allowance of $488	1,062,383	1,170,196
Heartland Bancshares Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	70,475
Carrying amount, net of allowance of $488	69,987
Commercial [Member] | Heartland Bancshares Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	44,717
Real Estate [Member] | Heartland Bancshares Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	13,146
Consumer [Member] | Heartland Bancshares Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	$ 12,612