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Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) | Sep. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2024
--- | --- | --- | ---
Available-for-sale investment securities: |  |  |
Estimated Fair Value | $ 5,260,813,000 | $ 4,617,759,000 | $ 4,612,299,000
Loans held for sale | 26,015,000 | 8,235,000 | 20,114,000
U.S. Treasury Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 101,970,000 | 273,562,000 | 293,014,000
Obligations of State and Political Subdivisions [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 1,733,911,000 | 1,440,245,000 | 1,471,483,000
Residential Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 2,470,798,000 | 2,350,534,000 | 2,423,930,000
Commercial Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 854,188,000 | 447,752,000 | 316,836,000
IRLCs [Member] |  |  |
Available-for-sale investment securities: |  |  |
Asset Derivative Fair Value | 726,000 | 238,000 | 499,000
Forward mortgage-backed securities trades | 0 | 0 | 0
Forward Mortgage-Backed Securities Trades [Member] |  |  |
Available-for-sale investment securities: |  |  |
Asset Derivative Fair Value | 0 | 84,000 | 0
Forward mortgage-backed securities trades | (214,000) | 0 | (98,000)
Fair Value, Measurements, Recurring [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 5,260,813,000 | 4,617,759,000 | 4,612,299,000
Loans held for sale | 25,180,000 | 7,793,000 | 16,513,000
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 101,970,000 | 273,562,000 | 293,014,000
Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 1,733,911,000 | 1,440,245,000 | 1,471,483,000
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 83,396,000 | 101,238,000 | 102,471,000
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 2,470,798,000 | 2,350,534,000 | 2,423,930,000
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 854,188,000 | 447,752,000 | 316,836,000
Fair Value, Measurements, Recurring [Member] | IRLCs [Member] |  |  |
Available-for-sale investment securities: |  |  |
Asset Derivative Fair Value | 726,000 | 238,000 | 499,000
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Trades [Member] |  |  |
Available-for-sale investment securities: |  |  |
Forward mortgage-backed securities trades | 214,000 | 84,000 | (98,000)
Fair Value, Measurements, Recurring [Member] | Collateralized Securities, Other [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 16,550,000 | 4,428,000 | 4,565,000
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 118,520,000 | 277,990,000 | 297,579,000
Loans held for sale | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | U.S. Treasury Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 101,970,000 | 273,562,000 | 293,014,000
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Obligations of State and Political Subdivisions [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Corporate Bonds [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Residential Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Commercial Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | IRLCs [Member] |  |  |
Available-for-sale investment securities: |  |  |
Asset Derivative Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member] |  |  |
Available-for-sale investment securities: |  |  |
Forward mortgage-backed securities trades | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Collateralized Securities, Other [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 16,550,000 | 4,428,000 | 4,565,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 5,142,293,000 | 4,339,769,000 | 4,314,720,000
Loans held for sale | 25,180,000 | 7,793,000 | 16,513,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | U.S. Treasury Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Obligations of State and Political Subdivisions [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 1,733,911,000 | 1,440,245,000 | 1,471,483,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Corporate Bonds [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 83,396,000 | 101,238,000 | 102,471,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Residential Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 2,470,798,000 | 2,350,534,000 | 2,423,930,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Commercial Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 854,188,000 | 447,752,000 | 316,836,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member] |  |  |
Available-for-sale investment securities: |  |  |
Asset Derivative Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member] |  |  |
Available-for-sale investment securities: |  |  |
Forward mortgage-backed securities trades | 214,000 | 84,000 | (98,000)
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Collateralized Securities, Other [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Loans held for sale | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | U.S. Treasury Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Obligations of State and Political Subdivisions [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Corporate Bonds [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Residential Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Commercial Mortgage-Backed Securities [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | IRLCs [Member] |  |  |
Available-for-sale investment securities: |  |  |
Asset Derivative Fair Value | 726,000 | 238,000 | 499,000
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member] |  |  |
Available-for-sale investment securities: |  |  |
Forward mortgage-backed securities trades | 0 | 0 | 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Collateralized Securities, Other [Member] |  |  |
Available-for-sale investment securities: |  |  |
Estimated Fair Value | $ 0 | $ 0 | $ 0

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- Definition Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 7A -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-7A Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 22 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-22 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 21 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-21 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 20 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-20 Reference 5: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 15 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-15 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483466/210-20-50-3 Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 4D -Subparagraph (c)(2) -SubTopic 20 -Topic 860 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481326/860-20-50-4D + Details
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