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Securities - Securities Available for Sale (Detail) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 14,037,520 $ 13,999,900
Gross Unrealized Gains 68,628 117,987
Gross Unrealized Losses (445,262) (408,746)
Fair Value 13,660,886 13,709,141
U.S. Treasury [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 2,252,751 2,301,248
Gross Unrealized Gains 8,082 20,008
Gross Unrealized Losses (3,120) (441)
Fair Value 2,257,713 2,320,815
U.S. Agencies [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 49,834 62,069
Gross Unrealized Gains 200 401
Gross Unrealized Losses (66) (100)
Fair Value 49,968 62,370
Mortgage-backed [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 8,589,349 8,427,197
Gross Unrealized Gains 42,549 71,827
Gross Unrealized Losses (344,025) (331,151)
Fair Value 8,287,873 8,167,873
State and political subdivisions [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 2,448,080 2,494,537
Gross Unrealized Gains 17,379 24,898
Gross Unrealized Losses (94,003) (72,847)
Fair Value 2,371,456 2,446,588
Corporates [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 142,631 180,854
Gross Unrealized Gains 267 349
Gross Unrealized Losses (3,217) (4,088)
Fair Value 139,681 177,115
Collateralized loan obligations [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 554,875 533,995
Gross Unrealized Gains 151 504
Gross Unrealized Losses (831) (119)
Fair Value $ 554,195 $ 534,380