Loans - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Specific reserves to customers whose loan terms have been modified in troubled debt restructurings	$ 195		$ 195		$ 198
Principal amount	375		375		409
Charge-offs due to troubled debt restructurings	0	0	0	145
Defaulted payment following modification for troubled debt restructurings	0	0	0	0	0
Increase in allowance for loan losses for loans purchased	0	96	0	171
Financing Receivable Modification Pre Modification Recorded Investment	0	0	0	284
Financing Receivable Modification Post Modification Recorded Investment	0	0	0	50
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually analyzed for credit quality based on credit risk, individual outstanding balance	$ 100	$ 100	$ 100	$ 100	$ 100
Troubled Debt Restructuring [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans restructured	0		0