Allowance for Loan Losses and Credit Quality Information - Analysis of Impaired Loans (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	$ 45,157	$ 46,651
Loans with No Related Reserve	19,693	17,802
Loans with Related Reserve	25,464	28,849
Related Reserve	7,387	5,317
Contractual Principal Balances	55,190	66,563
Average Loan Balances	44,299	45,629
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	10,590	12,381
Loans with No Related Reserve	1,188	580
Loans with Related Reserve	9,402	11,801
Related Reserve	5,234	3,034
Contractual Principal Balances	13,089	20,924
Average Loan Balances	8,494	5,952
Owner Occupied Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	2,313	2,474
Loans with No Related Reserve	1,314	1,865
Loans with Related Reserve	999	609
Related Reserve	103	609
Contractual Principal Balances	3,251	3,708
Average Loan Balances	2,931	4,461
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	9,221	8,335
Loans with No Related Reserve	3,946	4,732
Loans with Related Reserve	5,275	3,603
Related Reserve	465	319
Contractual Principal Balances	12,867	14,383
Average Loan Balances	9,479	11,005
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	1,492	1,419
Loans with Related Reserve	1,492	1,419
Related Reserve	215	334
Contractual Principal Balances	1,520	1,419
Average Loan Balances	1,150	1,013
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	15,484	15,666
Loans with No Related Reserve	8,407	7,068
Loans with Related Reserve	7,077	8,598
Related Reserve	1,180	790
Contractual Principal Balances	17,815	18,967
Average Loan Balances	16,090	17,296
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ending Loan Balances	6,057	6,376
Loans with No Related Reserve	4,838	3,557
Loans with Related Reserve	1,219	2,819
Related Reserve	190	231
Contractual Principal Balances	6,648	7,162
Average Loan Balances	$ 6,155	$ 5,902