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v3.26.1

Securities - Schedule of Amortized Cost, Fair Value and Gross Unrealized Gains and Losses for Securities Held to Maturity (Detail) - USD ($) $ in Thousands | Mar. 31, 2026 | Dec. 31, 2025
--- | --- | ---
Schedule Of Held To Maturity Securities [Line Items] |  |
Amortized Cost | $ 5,703,238 | $ 5,724,227
Gross Unrealized Gains | 13,006 | 27,075
Gross Unrealized Losses | (543,680) | (500,837)
Held to Maturity, Fair value | 5,172,564 | 5,250,465
Allowance for Credit Losses | (3,357) | (1,684)
Net Carrying Amount | 5,699,881 | 5,722,543
U.S. Treasury [Member] |  |
Schedule Of Held To Maturity Securities [Line Items] |  |
Amortized Cost | 38,256 | 38,253
Gross Unrealized Gains |  | 27
Gross Unrealized Losses | (298) | (37)
Held to Maturity, Fair value | 37,958 | 38,243
Net Carrying Amount | 38,256 | 38,253
Mortgage-backed [Member] |  |
Schedule Of Held To Maturity Securities [Line Items] |  |
Amortized Cost | 2,463,304 | 2,513,667
Gross Unrealized Gains | 87 | 335
Gross Unrealized Losses | (307,694) | (305,040)
Held to Maturity, Fair value | 2,155,697 | 2,208,962
Net Carrying Amount | 2,463,304 | 2,513,667
State and political subdivisions [Member] |  |
Schedule Of Held To Maturity Securities [Line Items] |  |
Amortized Cost | 3,201,678 | 3,172,307
Gross Unrealized Gains | 12,919 | 26,713
Gross Unrealized Losses | (235,688) | (195,760)
Held to Maturity, Fair value | 2,978,909 | 3,003,260
Allowance for Credit Losses | (3,357) | (1,684)
Net Carrying Amount | $ 3,198,321 | $ 3,170,623

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