v3.26.1
Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Available-for-sale investment securities:    
Estimated Fair Value $ 5,675,957 $ 5,514,113
Loans held for sale 23,616 29,992
U.S. Treasury Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value   60,813
Obligations of State and Political Subdivisions [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 1,753,893 1,751,373
Residential Mortgage-Backed Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 2,637,699 2,611,410
Commercial Mortgage-Backed Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 1,192,391 989,238
IRLCs [Member]    
Available-for-sale investment securities:    
Asset Derivative Fair Value 686 579
Forward mortgage-backed securities trades 0 0
Forward Mortgage-Backed Securities Trades [Member]    
Available-for-sale investment securities:    
Asset Derivative Fair Value 0 0
Forward mortgage-backed securities trades (141) (132)
Fair Value, Measurements, Recurring [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 5,675,957 5,514,113
Loans held for sale 18,932 25,431
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value   60,813
Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 1,753,893 1,751,373
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 63,452 78,709
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 2,637,699 2,611,410
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 1,192,391 989,238
Fair Value, Measurements, Recurring [Member] | IRLCs [Member]    
Available-for-sale investment securities:    
Asset Derivative Fair Value 686 579
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Trades [Member]    
Available-for-sale investment securities:    
Forward mortgage-backed securities trades 141 (132)
Fair Value, Measurements, Recurring [Member] | Collateralized Securities, Other [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 28,522 22,570
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 28,522 83,383
Loans held for sale 0 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | U.S. Treasury Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value   60,813
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
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Corporate Bonds [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 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
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Commercial Mortgage-Backed Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 0 0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | IRLCs [Member]    
Available-for-sale investment securities:    
Asset Derivative Fair Value 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
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Collateralized Securities, Other [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 28,522 22,570
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 5,647,435 5,430,730
Loans held for sale 18,932 25,431
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | U.S. Treasury Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value   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 1,753,893 1,751,373
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Corporate Bonds [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 63,452 78,709
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Residential Mortgage-Backed Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 2,637,699 2,611,410
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Commercial Mortgage-Backed Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 1,192,391 989,238
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member]    
Available-for-sale investment securities:    
Asset Derivative Fair Value 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 141 (132)
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Collateralized Securities, Other [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 0 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 0 0
Loans held for sale 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
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
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Corporate Bonds [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 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
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Commercial Mortgage-Backed Securities [Member]    
Available-for-sale investment securities:    
Estimated Fair Value 0 0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | IRLCs [Member]    
Available-for-sale investment securities:    
Asset Derivative Fair Value 686 579
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
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Collateralized Securities, Other [Member]    
Available-for-sale investment securities:    
Estimated Fair Value $ 0 $ 0