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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 |

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