Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,619,420	$ 1,631,891
Gross Unrealized Gains	586	254
Gross Unrealized Losses	(66,101)	(93,924)
Estimated Fair Value	1,553,905	1,538,221
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,560,265	1,568,563
Gross Unrealized Gains	415
Gross Unrealized Losses	(62,635)	(90,699)
Estimated Fair Value	1,498,045	1,477,864
U.S. Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,631	15,025
Gross Unrealized Gains	142	198
Gross Unrealized Losses	(3)	(1)
Estimated Fair Value	11,770	15,222
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,459	18,449
Gross Unrealized Gains	13	21
Gross Unrealized Losses	(1,677)	(1,884)
Estimated Fair Value	14,795	16,586
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,108	8,320
Gross Unrealized Gains	16	35
Gross Unrealized Losses	(114)	(221)
Estimated Fair Value	10,010	8,134
Asset backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,794	13,371
Gross Unrealized Losses	(282)	(361)
Estimated Fair Value	12,512	13,010
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,163	8,163
Gross Unrealized Losses	(1,390)	(758)
Estimated Fair Value	$ 6,773	$ 7,405