Allowance for Loan Losses - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 SecurityLoan	Jun. 30, 2012 SecurityLoan	Jun. 30, 2013 SecurityLoan	Jun. 30, 2012 SecurityLoan	Dec. 31, 2012
Receivables [Abstract]
Historical loss percentage period for portfolio segments			3 years
Adequate allowance for loan losses	$ 19,405		$ 19,405		$ 19,742
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
Defaulted loans	2	0	2	0
Loans	$ 66		$ 66
Impaired loans	greater than $350		greater than $350
Due days for testing impairment			60 days