Accounting for Certain Loans Acquired in a Transfer - Amounts of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	$ 1,321,494	$ 1,068,828
Carrying amount, net of allowance	1,304,168	1,051,943
Loans Purchased With Evidence Of Credit Deterioration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	148,445	60,294
Carrying amount, net of allowance	147,951	59,905
Loans Purchased With Evidence Of Credit Deterioration [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	92,827	37,048
Loans Purchased With Evidence Of Credit Deterioration [Member] | Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	36,734	11,761
Loans Purchased With Evidence Of Credit Deterioration [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	18,884	11,485
Loans Purchased With Evidence Of Credit Deterioration [Member] | Heartland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	39,764	60,294
Loans Purchased With Evidence Of Credit Deterioration [Member] | Heartland [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	19,801	37,048
Loans Purchased With Evidence Of Credit Deterioration [Member] | Heartland [Member] | Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	10,659	11,761
Loans Purchased With Evidence Of Credit Deterioration [Member] | Heartland [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	9,304	11,485
Loans Purchased With Evidence Of Credit Deterioration [Member] | Summit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	108,681
Loans Purchased With Evidence Of Credit Deterioration [Member] | Summit [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	73,026
Loans Purchased With Evidence Of Credit Deterioration [Member] | Summit [Member] | Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	26,075
Loans Purchased With Evidence Of Credit Deterioration [Member] | Summit [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	$ 9,580