Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,690,430	$ 1,631,891
Gross Unrealized Gains	1,583	254
Gross Unrealized Losses	(76,100)	(93,924)
Estimated Fair Value	1,615,913	1,538,221
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,629,245	1,568,563
Gross Unrealized Gains	1,341
Gross Unrealized Losses	(72,992)	(90,699)
Estimated Fair Value	1,557,594	1,477,864
U.S. Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,072	15,025
Gross Unrealized Gains	183	198
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	14,254	15,222
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,934	18,449
Gross Unrealized Gains	26	21
Gross Unrealized Losses	(1,773)	(1,884)
Estimated Fair Value	16,187	16,586
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,236	8,320
Gross Unrealized Gains	33	35
Gross Unrealized Losses	(114)	(221)
Estimated Fair Value	8,155	8,134
Asset backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,780	13,371
Gross Unrealized Losses	(417)	(361)
Estimated Fair Value	12,363	13,010
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,163	8,163
Gross Unrealized Losses	(803)	(758)
Estimated Fair Value	$ 7,360	$ 7,405