Allowance for Loan Losses and Credit Quality Information - Schedule of Types of TDR (Detail) - 3 months ended Mar. 31, 2017	SecurityLoan	loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity Date Extension	4
Discharged in bankruptcy	7	3
Other	1
Total	12
Owner-occupied commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity Date Extension	1
Discharged in bankruptcy	0
Other	0
Total	1
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity Date Extension	1
Discharged in bankruptcy	0
Other	0
Total	1
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity Date Extension	2
Discharged in bankruptcy	0
Other	0
Total	2
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity Date Extension	0
Discharged in bankruptcy	1
Other	0
Total	1
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity Date Extension	0
Discharged in bankruptcy	6
Other	1
Total	7