Loans - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration of loans in a single industry in excess of ten percent	0.00%
Maximum percentage loan related to single industry	10.00%
U.S. dollar denominated loans and commitments to borrowers in Mexico	$ 0		$ 0
Loans and Leases Receivable, Related Parties	$ 425,900		$ 416,100
Texas Leading Index economic condition indicator	128.2		127.1
Financing Receivable, Change in Method, Credit Loss Expense (Reversal)	$ 7,200
Financing Receivable, Allowance for Credit Loss	250,297		$ 245,996
Loans, net of unearned discounts	19,388,206		18,824,251
Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	5,279
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	21,871
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	1,958
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	$ 5,639
Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total loans	5.80%
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total loans	4.80%
Financing Receivable, Allowance for Credit Loss	$ 14,218	$ 19,191	17,814	$ 18,062
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Loans, net of unearned discounts	937,880		936,737
Financing Receivable, Year One, Originated, Current Fiscal Year	227,603
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	35,251
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	5,268
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	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
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	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	600
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	13,857	9,708	13,538	8,004
Financing Receivable, Allowance for Credit Loss, Writeoff	1,669	250
Loans, net of unearned discounts	2,558,670		2,460,726
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
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	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
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	75,596	78,465	74,006	104,237
Financing Receivable, Allowance for Credit Loss, Writeoff	2,144	6,180
Loans, net of unearned discounts	6,108,136		5,967,182
Financing Receivable, Year One, Originated, Current Fiscal Year	878,780
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	873,069
Commercial Portfolio Segment [Member] | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	11
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	2,059
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	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	96
Commercial Portfolio Segment [Member] | Additional Funding Agreement Terms
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	0
Commercial Portfolio Segment [Member] | Combination: Payment Delay and Term Extention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	28,900	0
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Change in Method, Credit Loss Expense (Reversal)	923
Financing Receivable, Allowance for Credit Loss	8,402	8,457	10,040	$ 7,017
Financing Receivable, Allowance for Credit Loss, Writeoff	8,257	$ 6,942
Loans, net of unearned discounts	462,882		476,962
Consumer Loan [Member] | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	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	1,958
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	5,543
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	2,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	5,500
Commercial mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Change in Method, Credit Loss Expense (Reversal)	6,200
Loans, net of unearned discounts	6,980,116		6,746,709
Commitments to Extend Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial instruments with off- balance-sheet risk	12,027,630		12,195,073
Commitments to Extend Credit [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	490,900
Commitments to Extend Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	1,100,000
Standby Letters of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial instruments with off- balance-sheet risk	416,084		438,635
Standby Letters of Credit [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	20,300
Standby Letters of Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	91,700
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Receivable	$ 94,000		$ 90,800