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Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale (Detail) - USD ($)
$ in Thousands
Mar. 31, 2025
Dec. 31, 2024
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 1,197,739 $ 1,253,968
Gross Unrealized Gains 116 83
Gross Unrealized Losses (31,191) (43,134)
Estimated Fair Value 1,166,664 1,210,917
U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,161,345 1,216,258
Gross Unrealized Gains 41 0
Gross Unrealized Losses (28,550) (40,249)
Estimated Fair Value 1,132,836 1,176,009
U.S. Federal Agencies [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 7,674 8,170
Gross Unrealized Gains 61 68
Gross Unrealized Losses (7) (6)
Estimated Fair Value 7,728 8,232
Mortgage Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 14,494 14,807
Gross Unrealized Gains 9 9
Gross Unrealized Losses (1,539) (1,772)
Estimated Fair Value 12,964 13,044
States and Political Subdivisions [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 6,063 6,570
Gross Unrealized Gains 5 6
Gross Unrealized Losses (128) (140)
Estimated Fair Value 5,940 6,436
Other Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 8,163 8,163
Gross Unrealized Losses (967) (967)
Estimated Fair Value $ 7,196 $ 7,196