Loans - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended
	Mar. 31, 2013 Item D	Dec. 31, 2012	Feb. 28, 2013	Mar. 31, 2012	Mar. 31, 2013 Commercial and Industrial, Other Commercial [Member] D	Mar. 31, 2013 Grade 12 [Member]	Mar. 31, 2013 Grade 13 [Member]	Mar. 31, 2013 Commercial Real Estate Loans [Member]	Mar. 31, 2013 Non-Accrual Loans [Member]	Mar. 31, 2012 Non-Accrual 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									$ 275,000
Additional interest that would have been recognized on non-accrual loans, net of tax									608,000	642,000
Charge-off of previously restructures loans	900,000
Previously restructured loans past due		419,000
Minimum number of days to be considered past due	90 days
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	4
Loan amount threshold	5,000,000
Loan value with weighted-average loan-to-value	38,200,000
Weighted-average loan-to-value ratio	65.40%
Texas Leading Index economic condition indicator		123.8	124.3	123.8
Maximum origination value of loans which were subject to further refinement of valuation methodology	$ 1,000,000