Loans and Allowances for Loan Losses - Schedule of Troubled Debt Restructurings Occurred During Period by Portfolio Segment (Detail) (Troubled Debt Restructurings [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Contract	Mar. 31, 2012 Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	4	2
Pre-Modification Outstanding Recorded Investment	$ 1,628	$ 1,462
Post-Modification Outstanding Recorded Investment	1,619	1,459
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	3	1
Pre-Modification Outstanding Recorded Investment	1,114	790
Post-Modification Outstanding Recorded Investment	1,105	790
Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	1	1
Pre-Modification Outstanding Recorded Investment	514	672
Post-Modification Outstanding Recorded Investment	514	669
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	2	2
Pre-Modification Outstanding Recorded Investment	602	1,462
Post-Modification Outstanding Recorded Investment	594	1,459
Originated loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	2	1
Pre-Modification Outstanding Recorded Investment	602	790
Post-Modification Outstanding Recorded Investment	594	790
Originated loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts		1
Pre-Modification Outstanding Recorded Investment		672
Post-Modification Outstanding Recorded Investment		669
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	2
Pre-Modification Outstanding Recorded Investment	1,026
Post-Modification Outstanding Recorded Investment	1,025
Acquired loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	1
Pre-Modification Outstanding Recorded Investment	512
Post-Modification Outstanding Recorded Investment	511
Acquired loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	1
Pre-Modification Outstanding Recorded Investment	514
Post-Modification Outstanding Recorded Investment	$ 514