Loans and Allowance for Loan Losses - Schedule of Troubled Debt Restructurings Occurred During Period by Portfolio Segment (Detail) (Troubled Debt Restructurings [Member], USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012 Contract	Sep. 30, 2011 Contract	Sep. 30, 2012 Contract	Sep. 30, 2011 Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	12	(1)	10	10
Pre-Modification Outstanding Recorded Investment	$ 12,347	$ 15,144	$ 15,320	$ 2,901
Post-Modification Outstanding Recorded Investment	12,821	12,730	14,194	1,407
Number of Contracts		2		2
Recorded Investment		742		742
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	9	1	7	11
Pre-Modification Outstanding Recorded Investment	11,350	15,855	14,360	3,447
Post-Modification Outstanding Recorded Investment	11,974	13,425	13,369	1,822
Number of Contracts		2		2
Recorded Investment		742		742
Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	3	(2)	3	(1)
Pre-Modification Outstanding Recorded Investment	997	(711)	960	(546)
Post-Modification Outstanding Recorded Investment	847	(695)	825	(415)
Troubled debt restructurings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	12	(1)	10	10
Pre-Modification Outstanding Recorded Investment	12,347	15,144	15,320	2,901
Post-Modification Outstanding Recorded Investment	12,821	12,730	14,194	1,407
Number of Contracts		2		2
Recorded Investment		742		742
Troubled debt restructurings [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	9	1	7	11
Pre-Modification Outstanding Recorded Investment	11,350	15,855	14,360	3,447
Post-Modification Outstanding Recorded Investment	11,974	13,425	13,369	1,822
Number of Contracts		2		2
Recorded Investment		742		742
Troubled debt restructurings [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Contracts	3	(2)	3	(1)
Pre-Modification Outstanding Recorded Investment	997	(711)	960	(546)
Post-Modification Outstanding Recorded Investment	$ 847	$ (695)	$ 825	$ (415)