Loans - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($) Rate	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) Rate	Sep. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jun. 30, 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	$ 396,700		$ 396,700			$ 391,300
Texas Leading Index economic condition indicator	129.0		129.0			130.4
Financing Receivable, Change in Method, Credit Loss Expense (Reversal)			$ (45,000)
Financing Receivable, Allowance for Credit Loss	$ 242,235		242,235			$ 227,621
Loans, net of unearned discounts	$ 18,399,259		$ 18,399,259			17,154,969
Loans Receivable, Basis Spread on Variable Rate | Rate	1.75%		1.75%
Loan Receivable Variable Rate | Rate	10.25%		10.25%
Loan Receivable Fixed Rate | Rate	6.74%		6.74%
Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 26,586		$ 26,586
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	464		464
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	15,667		15,667
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	5,341		5,341
Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	0	$ 1,083	0	$ 1,083
Additional Funding Agreement Terms
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	$ 0		$ 0
Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total loans	5.60%		5.60%
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total loans	5.50%		5.50%
Financing Receivable, Allowance for Credit Loss	$ 17,066	18,851	$ 17,066	18,851	$ 14,929	18,062	$ 16,267	$ 17,217
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0	518	371
Loans, net of unearned discounts	1,006,859		1,006,859			925,729
Financing Receivable, Year One, Originated, Current Fiscal Year	331,902		331,902
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	72,578		72,578
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	8,148		8,148
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
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	1,200	372	2,700	1,200
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	15,039	8,035	15,039	8,035	13,035	8,004	6,854	6,585
Financing Receivable, Allowance for Credit Loss, Writeoff	170	68	1,500	430
Loans, net of unearned discounts	2,339,363		2,339,363			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	74,307	98,830	74,307	98,830	75,166	104,237	87,270	72,091
Financing Receivable, Allowance for Credit Loss, Writeoff	943	572	14,259	5,918
Loans, net of unearned discounts	5,836,877		5,836,877			5,674,798
Financing Receivable, Year One, Originated, Current Fiscal Year	1,391,552		1,391,552
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	877,000		877,000
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	359		359
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	952		952
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	9,331	7,992	9,331	7,992	$ 9,563	7,017	$ 12,135	$ 7,837
Financing Receivable, Allowance for Credit Loss, Writeoff	8,189	6,549	22,147	17,642
Loans, net of unearned discounts	459,764		459,764			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	15,543		15,543
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,389		4,389
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	15,500		15,500
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,200		4,200
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	17,945		17,945			34,852
Commitments to Extend Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial instruments with off- balance-sheet risk	12,053,260		12,053,260			12,137,957
Commitments to Extend Credit [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	459,500		459,500
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	370,718		370,718			383,851
Standby Letters of Credit [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	20,200		20,200
Standby Letters of Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	87,200		87,200
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Receivable	$ 83,900		$ 83,900			$ 68,700