Loans - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2026 USD ($)	Mar. 31, 2025 USD ($)	Feb. 28, 2026	Dec. 31, 2025 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
Bank Overdrafts	15,600			13,800
Loans and Leases Receivable, Related Parties	328,200			316,100
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	18,500,000			17,900,000
Federal Home Loan Bank Borrowings, Fair Value Disclosure	0			0
Loans, net of unearned discounts	22,432,419			$ 21,891,812
Texas Leading Index economic condition indicator			127.9	125.7
Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	0	$ 6,331
Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	$ 127,559
Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total loans	4.70%
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of total loans	5.40%
Loans, net of unearned discounts	$ 1,208,070			$ 1,094,669
Commercial and Industrial Total Energy Loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	1,443
Non Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Excluding Accrued Interest, Impaired Interest Lost On Nonaccrual Loans	1,100	1,400
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	3,880,604			3,718,668
Total consumer real estate loans [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	28,600
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	6,333,349			6,306,980
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] | Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts		$ 4,385
Commercial Portfolio Segment [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	23,366
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	453,103			460,685
Consumer Loan [Member] | Financing Receivables, 30 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	6,614
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	1,900
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,700
Commitments to Extend Credit [Member] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	542,400
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] | Automobile Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	20,000
Standby Letters of Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	115,300
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Receivable	$ 87,700			$ 90,600