Loans - Additional Information (Detail) (USD $)	6 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2014 Item	Jun. 30, 2013	May 31, 2014	Dec. 31, 2013	Jun. 30, 2014 Commercial Real Estate Loans [Member]	Jun. 30, 2014 Commercial and industrial, Energy [Member]	Jun. 30, 2014 Non-Accrual Loans [Member]	Jun. 30, 2013 Non-Accrual Loans [Member]	Jun. 30, 2014 Non-Accrual Loans [Member]	Jun. 30, 2013 Non-Accrual Loans [Member]	Jun. 30, 2014 Grade 12 [Member]	Jun. 30, 2014 Grade 13 [Member]	Jun. 30, 2014 Commercial and industrial, Other commercial [Member]	Jun. 30, 2013 Commercial and industrial, Other commercial [Member]	Jun. 30, 2014 Commercial and industrial, Other commercial [Member] Commercial Portfolio Segment [Member]	Jun. 30, 2014 Commercial real estate, Buildings, land and other [Member]	Jun. 30, 2013 Commercial real estate, Buildings, land and other [Member]	Jun. 30, 2014 Commercial real estate, Buildings, land and other [Member] Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 6,874,000	$ 6,303,000											$ 3,752,000	$ 2,138,000	$ 2,900,000	$ 3,122,000	$ 4,165,000	$ 3,100,000
Percentage of owner-occupied commercial real estate loans					57.00%
Maximum loan-to-value percentage on home equity loans	80.00%
Maximum percentage loan related to single industry	10.00%
Percentage of loans related to a single industry						14.30%
Minimum number of days to be considered past due	90 days
Troubled Debt Restructurings	6,741,000	5,069,000							6,700,000				3,672,000	1,343,000		3,069,000	3,726,000
Additional interest that would have been recognized on non-accrual loans, net of tax							355,000	591,000	713,000	1,200,000
Previously restructured loans past due	725,000
Charge-off of previously restructures loans													427,000			0
Previously Restructured Loans Moved to OREO																500,000
Number of days past due for payment of interest on loans, minimum	120 days										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	2
Loan amount threshold	5,000,000
Loan value with weighted-average loan-to-value	14,800,000
Weighted-average loan-to-value ratio	73.20%
Texas Leading Index economic condition indicator			131.4	129.1
Maximum origination value of loans which were subject to further refinement of valuation methodology	$ 1,000,000