Loans - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended	3 Months Ended		9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013 Loans	Sep. 30, 2012 Loans	Sep. 30, 2013 Loans	Sep. 30, 2012	Dec. 31, 2012 Loans	Sep. 30, 2013 Commercial Mortgage Loan One [Member]	Mar. 31, 2013 Commercial Mortgage Loan One [Member]	Sep. 30, 2012 Commercial Mortgage Loan One [Member]	Sep. 30, 2013 Commercial Mortgage Loan One [Member]	Sep. 30, 2012 Commercial Mortgage Loan One [Member]	Dec. 31, 2012 Commercial Mortgage Loan One [Member]	Sep. 30, 2013 Commercial Mortgage Loan Two [Member]	Jun. 30, 2013 Commercial Mortgage Loan Two [Member]	Sep. 30, 2013 Commercial Mortgage Loan Two [Member]	Sep. 30, 2013 Commercial Mortgage Loan Three [Member]	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net unamortized loan costs and fees	$ 322,000		$ 322,000		$ 232,000
Percentage of comprised loan, commercial, industrial and agricultural loans	26.00%		26.00%		28.00%
Percentage of comprised loan, commercial mortgage loans	30.00%		30.00%		28.00%
Risk rating to commercial loans	250,000		250,000
Percentage of loan-to-value to business equipment			80.00%
Percentage of loan-to-value to accounts receivable			75.00%
Percentage of loan-to-value to business inventory			60.00%
Percentage of loan-to-value to real estate			85.00%
Percentage of residential real estate loan in portfolio	40.00%		40.00%		37.00%
Maximum percentage of consumer loan and credit card in portfolio	10.00%		10.00%		10.00%
Number of loans modified as troubled debt restructuring	1	0	12		10
Additional provision for loan losses	562,000	0	562,000	0		127,000		503,000	262,000	503,000		0		588,000	562,000
Reduction in stated interest rate modification having loan range period																4 years	15 years
Extension of maturity date modification having loan range period																4 years	18 years
Principal balances forgiven in connection with loan restructuring	0		0		0
Troubled debt restructuring charged off							595,000
Commercial mortgage loan balance amount											1,660,000		1,086,000
Minimum period to be considered for loan to have defaulted			90 days
Impaired commercial mortgage loan placed on non-accrual status, modified as TDRs	$ 13,255,000		$ 13,255,000		$ 11,621,000										$ 3,269,000
Outstanding balance of semi annual loans			Greater than $1 million
Outstanding balance of annual loans			Less than $1 million