Allowance for Loan Losses and Credit Quality Information - Schedule of Residential and Consumer Credit Exposure (Parenthetical) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-performing loans of troubled debt restructured mortgages and home equity installment loans	$ 14,100	$ 13,600
Acquired nonimpaired loans	330,660	371,100	$ 129,858
Total Residential and Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired nonimpaired loans	$ 81,500	$ 94,200