Allowance for Loan Losses and Credit Quality Information - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for impairment loans			90 days
Net charge-offs			$ 2,500,000	$ 6,300,000
Percentage of average loans annualized, charged-offs			0.17%	0.45%
Calculated probability of default rate			Probability of default is calculated based on the historical rate of migration to impaired status during the last 16 quarters.
Loss emergency period			Nine quarters
Basis points	10.00%		10.00%
Allowance methodology to reflect loss emergence period			During the quarter ended June 30, 2014 the allowance methodology was updated to reflect a loss emergence period (“LEP”) of nine quarters based on the generally improving economic conditions. Industry and historical data indicates that the LEP lengthens in an improving economy as the length of time between an adverse financial event and subsequent loss is extended. In addition, a 10 basis point consideration was given to the C&I loan portfolio due to the assessment of qualitative factors on three lending relationships.
Interest income on impaired loans	393,000	235,000	747,000	473,000
Balance of troubled debt restructurings	26,200,000		26,200,000		27,600,000
TDRs in nonaccrual status			14,400,000		15,300,000
TDRs in accrual status			11,800,000		12,300,000
Troubled debt restructuring related reserves	2,300,000		2,300,000		4,100,000
Usual sustained repayment performance period			6 months
Increase in allowance for loan losses			130,000	28,000
Troubled debt restructurings charged off	$ 41,000	$ 363,000	$ 41,000	$ 363,000
Total Residential and Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment loans, charge off period			90 days
Number of term loans modified in troubled debt restructurings			13
Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Calculated pooled reserves for retail loans			Pooled reserves for retail loans are calculated based solely on the previous three year average net loss rate.