Allowance for Loan Losses - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 SecurityLoan	Mar. 31, 2014 SecurityLoan	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Historical loss percentage period for portfolio segments	2 years
Allowance for loan losses	$ 14,315		$ 14,268
Number of days past due for loans to be considered as nonperforming	90 days
Reasonable period for nonperforming TDRs to be returned to performing status	6 months
Number of days reaching where loans are considered for nonaccrual status	90 days
Conditions where loans are considered for nonaccrual status	A loan may be returned to accruing status only if one of three conditions are met the loan is well-secured and none of the principal and interest has been past due for a minimum of 90 days; the loan is a TDR and has made a minimum of six months payments; or the principal and interest payments are reasonably assured and a sustained period of performance has occurred, generally six months.
Defaulted loans	0	0
Increase in Loan modified in TDR	272
Impaired loans	Greater than $500
Foreclosed assets	528		560
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Foreclosed assets	502
Residential mortgages in process of foreclosure	899
TDRs [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 855		$ 895