Loans - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration of loans in a single industry in excess of ten percent	0.00%		0.00%
Maximum percentage loan related to single industry	10.00%		10.00%
U.S. dollar denominated loans and commitments to borrowers in Mexico	$ 0		$ 0			$ 0
Loans and Leases Receivable, Related Parties	$ 342,500		$ 342,500			$ 350,500
Texas Leading Index economic condition indicator	138.4		138.4			135.9
Financing Receivable, Allowance for Credit Loss	$ 239,632		$ 239,632			$ 248,666
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total energy loans to total loans	5.90%		5.90%
Percentage of total energy loans to total loans excluding PPP Loans	5.90%		5.90%
Financing Receivable, Allowance for Credit Loss	$ 16,267	$ 28,010	$ 16,267	$ 28,010	$ 15,422	17,217	$ 33,472	$ 39,553
Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	0	0	0	0		0
Non Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional interest that would have been recognized on non-accrual loans, net of tax	436	$ 427	843	$ 881
Commitments to Extend Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	887,300		887,300
Standby Letters of Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	79,100		79,100
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Receivable	$ 44,800		$ 44,800			$ 40,000