Loans and Allowance for Loan Losses - Troubled Debt Restructuring Loan Information (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012 contracts	Dec. 31, 2011 contracts
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans	7	4
Pre-Modification Outstanding Recorded Investment	$ 5,595	$ 2,259
Post-Modification Outstanding Recorded Investment	5,114	2,259
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans	11
Pre-Modification Outstanding Recorded Investment	1,167
Post-Modification Outstanding Recorded Investment	1,167
Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans	8
Pre-Modification Outstanding Recorded Investment	398
Post-Modification Outstanding Recorded Investment	398
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans	1
Pre-Modification Outstanding Recorded Investment	61
Post-Modification Outstanding Recorded Investment	61
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans		1
Pre-Modification Outstanding Recorded Investment		840
Post-Modification Outstanding Recorded Investment		$ 840