v3.26.1
Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities $ 45,839 $ 22,331
Available-for-sale securities 13,488,159 13,709,141
Derivative Assets, Fair Value 236,420 281,329
Derivative Liabilities, Fair Value 148,337 136,452
Securities sold not yet purchased 14,000 4,100
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 11,355 5,145
Available-for-sale securities 2,292,226 2,497,930
Significant Other Observable Inputs (Level 2) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 34,484 17,186
Available-for-sale securities 11,195,933 11,211,211
U.S. Treasury [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 2,204,917 2,320,815
U.S. Agencies [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 48,785 62,370
Mortgage-backed [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 8,223,615 8,167,873
State and political subdivisions [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 2,372,497 2,446,588
Corporates [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 87,309 177,115
Fair Value Measurement, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 45,839 22,331
Available-for-sale securities 13,488,159 13,709,141
Equity securities with readily determinable fair values 12,610 14,690
Derivative Assets, Fair Value 236,420 281,329
Total 13,783,028 14,027,491
Derivative Liabilities, Fair Value 148,337 136,452
Securities sold not yet purchased 14,027 4,052
Total 162,364 140,504
Fair Value Measurement, Recurring [Member] | Collateralized loan obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 551,036 534,380
Fair Value Measurement, Recurring [Member] | Trading - other [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 333 317
Fair Value Measurement, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 11,355 5,145
Available-for-sale securities 2,292,226 2,497,930
Equity securities with readily determinable fair values 12,610 14,690
Total 2,316,191 2,517,765
Fair Value Measurement, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Trading - other [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 333 317
Fair Value Measurement, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 34,484 17,186
Available-for-sale securities 11,195,933 11,211,211
Derivative Assets, Fair Value 236,420 281,329
Total 11,466,837 11,509,726
Derivative Liabilities, Fair Value 148,337 136,452
Securities sold not yet purchased 14,027 4,052
Total 162,364 140,504
Fair Value Measurement, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Collateralized loan obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale securities 551,036 534,380
Fair Value Measurement, Recurring [Member] | U.S. Treasury [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities   2,636
Available-for-sale securities 2,204,917 2,320,815
Fair Value Measurement, Recurring [Member] | U.S. Treasury [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities   2,636
Available-for-sale securities 2,204,917 2,320,815
Fair Value Measurement, Recurring [Member] | U.S. Agencies [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 18,407 13,489
Available-for-sale securities 48,785 62,370
Fair Value Measurement, Recurring [Member] | U.S. Agencies [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 18,407 13,489
Available-for-sale securities 48,785 62,370
Fair Value Measurement, Recurring [Member] | Mortgage-backed [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 2,493  
Available-for-sale securities 8,223,615 8,167,873
Fair Value Measurement, Recurring [Member] | Mortgage-backed [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 2,493  
Available-for-sale securities 8,223,615 8,167,873
Fair Value Measurement, Recurring [Member] | State and political subdivisions [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 13,584 3,697
Available-for-sale securities 2,372,497 2,446,588
Fair Value Measurement, Recurring [Member] | State and political subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 13,584 3,697
Available-for-sale securities 2,372,497 2,446,588
Fair Value Measurement, Recurring [Member] | Corporates [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 11,022 2,192
Available-for-sale securities 87,309 177,115
Fair Value Measurement, Recurring [Member] | Corporates [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Trading securities 11,022 2,192
Available-for-sale securities $ 87,309 $ 177,115