Loans and the Allowance for Credit Losses - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013 Segment Contract SecurityLoan	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Net of deferred loan fees and costs	$ 2,600,000	$ 2,500,000
Non-accrual status period	90 days
Number of restructured contracts greater than $1 million	3
Value of restructured contracts greater than $1 million	4,700,000
Percentage of Total TDRs	13.50%
Number of commercial real estate land and construction loans	1
Number of commercial real estate improved property	2
Accruing and non accrual TDR permitted interest only payment period	3 months
Percentage of TDRs defaulted during the period that were restructured within the last twelve months	7.90%
Loans with accruing interest	3
Unfunded commitments to debtors	24,000	49,000
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Aggregate amount of residential real estate, home equity and consumer loans classified as substandard	13,000,000	17,900,000
Internally assigned loan grades to residential real estate, home equity and consumer loans	3,200,000	4,900,000
Specific Reserves [Member]
Financing Receivable, Recorded Investment [Line Items]
Specific reserve on largest TDRs	$ 1,100,000