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Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale (Detail) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 1,253,968 $ 1,619,420
Gross Unrealized Gains 83 586
Gross Unrealized Losses (43,134) (66,101)
Estimated Fair Value 1,210,917 1,553,905
U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,216,258 1,560,265
Gross Unrealized Gains   415
Gross Unrealized Losses (40,249) (62,635)
Estimated Fair Value 1,176,009 1,498,045
U.S. Federal Agencies [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 8,170 11,631
Gross Unrealized Gains 68 142
Gross Unrealized Losses (6) (3)
Estimated Fair Value 8,232 11,770
Mortgage Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 14,807 16,459
Gross Unrealized Gains 9 13
Gross Unrealized Losses (1,772) (1,677)
Estimated Fair Value 13,044 14,795
States and Political Subdivisions [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 6,570 10,108
Gross Unrealized Gains 6 16
Gross Unrealized Losses (140) (114)
Estimated Fair Value 6,436 10,010
Asset backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost   12,794
Gross Unrealized Losses   (282)
Estimated Fair Value   12,512
Other Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 8,163 8,163
Gross Unrealized Losses (967) (1,390)
Estimated Fair Value $ 7,196 $ 6,773