Allowance for Loan Losses and Credit Quality Information - Schedule of Commercial Credit Exposure (Parenthetical) (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired nonimpaired loans	$ 121,780	$ 145,800	$ 156,671
Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired nonimpaired loans	$ 100,700	$ 119,800

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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