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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	$ 681	$ 6,106	$ 2,330	$ 8,586
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Total loans identified during the period		88		209
Residential [Member]
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	38	72	447	1,916
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Total loans identified during the period	$ 643	1,097	1,306	1,612
Owner Occupied Commercial [Member]
Financing Receivable, Modifications [Line Items]
Total loans identified during the period			$ 577
Commercial Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Total loans identified during the period		3,430		3,430
Construction [Member]
Financing Receivable, Modifications [Line Items]
Total loans identified during the period		$ 1,419		$ 1,419