Allowance for Loan Losses and Credit Quality Information - Schedule of Types of TDR (Detail) - 6 months ended Jun. 30, 2017	SecurityLoan	loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractual payment reduction and term extension	1
Maturity Date Extension	4
Discharged in bankruptcy	8	2
Other	5
Total	18
Owner-occupied commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractual payment reduction and term extension	0
Maturity Date Extension	1
Discharged in bankruptcy	0
Other	0
Total	1
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractual payment reduction and term extension	1
Maturity Date Extension	1
Discharged in bankruptcy	0
Other	0
Total	2
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractual payment reduction and term extension	0
Maturity Date Extension	2
Discharged in bankruptcy	0
Other	1
Total	3
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractual payment reduction and term extension	0
Maturity Date Extension	0
Discharged in bankruptcy	1
Other	0
Total	1
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contractual payment reduction and term extension	0
Maturity Date Extension	0
Discharged in bankruptcy	7
Other	4
Total	11