Allowance for Loan Losses and Credit Quality Information - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for impairment loans	90 days
Net charge-offs	$ 2,500,000		$ 9,900,000
Percentage of average loans annualized, charged-offs	0.34%		0.34%
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.
Interest income on impaired loans	353,000	238,000
Balance of troubled debt restructurings	26,700,000		27,600,000
TDRs in nonaccrual status	15,100,000		15,300,000
TDRs in accrual status	11,600,000		12,300,000
Troubled debt restructuring related reserves	2,200,000		4,100,000
Usual sustained repayment performance period	6 months
Increase in allowance for loan losses	1,000	0
Troubled debt restructurings charged off	$ 40,000	$ 119,000
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	6