Allowance for Loan Losses and Credit Quality Information - Schedule of Loans Identified as Troubled Debt Restructurings During Periods Indicated (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
2016 Pre Modification	$ 6,145	$ 3,087
Post Modification	6,145	3,087
Commercial [Member]
Financing Receivable, Modifications [Line Items]
2016 Pre Modification	1,407
Post Modification	1,407
Residential [Member]
Financing Receivable, Modifications [Line Items]
2016 Pre Modification	2,754	895
Post Modification	2,754	895
Consumer Loan Commitments [Member]
Financing Receivable, Modifications [Line Items]
2016 Pre Modification	873	1,615
Post Modification	873	1,615
Owner- Occupied Commercial [Member]
Financing Receivable, Modifications [Line Items]
2016 Pre Modification		577
Post Modification		$ 577
Commercial Mortgages [Member]
Financing Receivable, Modifications [Line Items]
2016 Pre Modification	1,111
Post Modification	$ 1,111