Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,503,706	$ 1,619,420
Gross Unrealized Gains	179	586
Gross Unrealized Losses	(63,358)	(66,101)
Estimated Fair Value	1,440,527	1,553,905
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,450,915	1,560,265
Gross Unrealized Gains		415
Gross Unrealized Losses	(60,133)	(62,635)
Estimated Fair Value	1,390,782	1,498,045
U.S. Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,565	11,631
Gross Unrealized Gains	121	142
Gross Unrealized Losses	(3)	(3)
Estimated Fair Value	9,683	11,770
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,647	16,459
Gross Unrealized Gains	7	13
Gross Unrealized Losses	(1,746)	(1,677)
Estimated Fair Value	13,908	14,795
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,078	10,108
Gross Unrealized Gains	8	16
Gross Unrealized Losses	(135)	(114)
Estimated Fair Value	9,951	10,010
Asset backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,338	12,794
Gross Unrealized Gains	43
Gross Unrealized Losses		(282)
Estimated Fair Value	9,381	12,512
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,163	8,163
Gross Unrealized Losses	(1,341)	(1,390)
Estimated Fair Value	$ 6,822	$ 6,773