Allowance for Loan Losses and Credit Quality Information - Schedule of Loans Identified as Troubled Debt Restructurings During Periods Indicated (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	$ 1,136	$ 493	$ 7,188	$ 2,306
Commercial
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	338	141	781	1,125
Commercial mortgages
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	0	0	0	0
Construction
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	124	0	1,836	0
Residential
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	0	112	242	726
Consumer
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	674	240	1,258	455
Owner-occupied commercial
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	$ 0	$ 0	$ 3,071	$ 0