Loans - Additional Information (Detail) (USD $)	9 Months Ended			9 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Loan	Aug. 31, 2013	Dec. 31, 2012	Sep. 30, 2013 Commercial Real Estate Loans [Member]	Sep. 30, 2013 Non-Accrual Loans [Member]	Sep. 30, 2012 Non-Accrual Loans [Member]	Sep. 30, 2013 Non-Accrual Loans [Member]	Sep. 30, 2012 Non-Accrual Loans [Member]	Sep. 30, 2013 Grade 12 [Member]	Sep. 30, 2013 Grade 13 [Member]	Sep. 30, 2013 Commercial and industrial, Other commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of owner-occupied commercial real estate loans				58.00%
Maximum loan-to-value percentage on home equity loans	80.00%
Maximum percentage loan related to single industry	10.00%
Minimum number of days to be considered past due	90 days
Troubled Debt Restructurings							$ 4,400,000
Additional interest that would have been recognized on non-accrual loans, net of tax					568,000	646,000	1,800,000	1,900,000
Previously restructured loans past due	2,100,000
Charge-off of previously restructures loans	1,100,000
Number of days past due for payment of interest on loans, minimum	120 days										180 days
General percentage of valuation allowance in excess of principal balance, maximum									30.00%
General percentage of valuation allowance in excess of principal balance, minimum										30.00%
Number of loans with calculated risk of 10 or higher greater than $5 million	3
Loan amount threshold	5,000,000
Loan value with weighted-average loan-to-value	30,800,000
Weighted-average loan-to-value ratio	75.40%
Texas Leading Index economic condition indicator		126.3	123.5
Maximum origination value of loans which were subject to further refinement of valuation methodology	$ 1,000,000