Loans - Additional Information (Detail) (USD $)	6 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2013 Item D	May 31, 2013	Dec. 31, 2012	Jun. 30, 2013 Non-Accrual Loans [Member]	Jun. 30, 2012 Non-Accrual Loans [Member]	Jun. 30, 2013 Non-Accrual Loans [Member]	Jun. 30, 2012 Non-Accrual Loans [Member]	Jun. 30, 2013 Commercial and industrial, Other commercial [Member] D	Jun. 30, 2013 Grade 12 [Member]	Jun. 30, 2013 Grade 13 [Member]	Jun. 30, 2013 Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of owner-occupied commercial real estate loans											56.00%
Maximum loan-to-value percentage on home equity loans	80.00%
Maximum percentage loan related to single industry	10.00%
Troubled Debt Restructurings						$ 3,200,000
Additional interest that would have been recognized on non-accrual loans, net of tax				591,000	639,000	1,200,000	1,300,000
Charge-off of previously restructures loans	1,100,000
Minimum number of days to be considered past due	90 days
Previously restructured loans past due	169,000
Number of days past due for payment of interest on loans, minimum	120							180
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	31,000,000
Weighted-average loan-to-value ratio	75.60%
Texas Leading Index economic condition indicator		124.5	123.8
Maximum origination value of loans which were subject to further refinement of valuation methodology	$ 1,000,000