Loans - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
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	$ 389,200		$ 389,200			$ 391,300
Texas Leading Index economic condition indicator	127.7		127.7			130.3
Financing Receivable, Change in Method, Credit Loss Expense (Reversal)			$ (45,000)
Financing Receivable, Allowance for Credit Loss	$ 233,619		233,619			$ 227,621
Loans, net of unearned discounts	17,746,311		17,746,311			17,154,969
Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	12,248		12,248
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	8		8
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	8,267		8,267
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,562		4,562
Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	0	$ 1,116	0	$ 1,116
Additional Funding Agreement Terms
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	$ 0		$ 0
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total energy loans to total loans	5.60%		5.60%
Financing Receivable, Allowance for Credit Loss	$ 14,929	16,267	$ 14,929	16,267	$ 19,191	18,062	$ 15,422	$ 17,217
Financing Receivable, Allowance for Credit Loss, Writeoff	518	0	518	371
Loans, net of unearned discounts	986,571		986,571			925,729
Financing Receivable, Year One, Originated, Current Fiscal Year	311,743		311,743
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	70,287		70,287
Commercial and Industrial Total Energy Loans [Member] | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	10,324		10,324
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0		0
Commercial and Industrial Total Energy Loans [Member] | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0		0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0		0
Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	0	0	0	0		0
Loans, net of unearned discounts	22,333		22,333			34,852
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	835	436	1,400	843
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	13,035	6,854	13,035	6,854	9,708	8,004	6,359	6,585
Financing Receivable, Allowance for Credit Loss, Writeoff	1,080	131	1,330	362
Loans, net of unearned discounts	2,157,916		2,157,916			1,843,539
Total consumer real estate loans [Member] | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0		0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0		0
Total consumer real estate loans [Member] | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0		0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0		0
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	75,166	87,270	75,166	87,270	78,465	104,237	87,026	72,091
Financing Receivable, Allowance for Credit Loss, Writeoff	7,136	1,891	13,316	5,346
Loans, net of unearned discounts	5,726,804		5,726,804			5,674,798
Financing Receivable, Year One, Originated, Current Fiscal Year	1,145,305		1,145,305
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	941,744		941,744
Commercial Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0		0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0		0
Commercial Portfolio Segment [Member] | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	124		124
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	208		208
Commercial Portfolio Segment [Member] | Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	0		0
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	9,563	12,135	9,563	12,135	$ 8,457	7,017	$ 9,074	$ 7,837
Financing Receivable, Allowance for Credit Loss, Writeoff	7,016	$ 5,322	13,958	$ 11,093
Loans, net of unearned discounts	459,720		459,720			492,726
Consumer Loan [Member] | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0		0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0		0
Consumer Loan [Member] | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	8,143		8,143
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,354		4,354
Bank Overdrafts | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	8,100		8,100
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,200		4,200
Commitments to Extend Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial instruments with off- balance-sheet risk	12,208,032		12,208,032			12,137,957
Commitments to Extend Credit [Member] | Automobile Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	454,900		454,900
Commitments to Extend Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	1,000,000		1,000,000
Standby Letters of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial instruments with off- balance-sheet risk	405,900		405,900			383,851
Standby Letters of Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	84,100		84,100
Standby Letters of Credit [Member] | Automobiles
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	20,100		20,100
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Receivable	$ 73,900		$ 73,900			$ 68,700