Allowance for Loan Losses and Credit Quality Information - Analysis of Impaired Loans (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	$ 37,088	$ 37,710
Loans with No Related Reserve	18,362	20,983
Loans with Related Reserve	18,726	16,727
Related Reserve	2,129	2,624
Contractual Principal Balances	45,132	64,406
Average Loan Balances	39,332	42,555
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	3,765	6,137
Loans with No Related Reserve	1,565	951
Loans with Related Reserve	2,200	5,186
Related Reserve	479	1,168
Contractual Principal Balances	4,567	20,206
Average Loan Balances	6,472	9,391
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	15,254	15,710
Loans with No Related Reserve	7,823	9,034
Loans with Related Reserve	7,431	6,676
Related Reserve	1,012	920
Contractual Principal Balances	17,768	18,655
Average Loan Balances	15,316	15,264
Consumer Loan Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	7,965	7,665
Loans with No Related Reserve	6,785	6,498
Loans with Related Reserve	1,180	1,167
Related Reserve	205	200
Contractual Principal Balances	9,714	9,353
Average Loan Balances	7,446	6,801
Owner- Occupied Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	3,483	2,127
Loans with No Related Reserve	486	1,090
Loans with Related Reserve	2,997	1,037
Related Reserve	37	22
Contractual Principal Balances	3,833	2,947
Average Loan Balances	2,459	2,111
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	3,765	4,652
Loans with No Related Reserve	1,703	3,410
Loans with Related Reserve	2,062	1,242
Related Reserve	126	103
Contractual Principal Balances	6,271	11,826
Average Loan Balances	5,903	7,540
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	2,856	1,419
Loans with Related Reserve	2,856	1,419
Related Reserve	270	211
Contractual Principal Balances	2,979	1,419
Average Loan Balances	$ 1,736	$ 1,448