Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,602,069	$ 1,619,420
Gross Unrealized Gains	135	586
Gross Unrealized Losses	(68,682)	(66,101)
Estimated Fair Value	1,533,522	1,553,905
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,545,588	1,560,265
Gross Unrealized Gains		415
Gross Unrealized Losses	(65,207)	(62,635)
Estimated Fair Value	1,480,381	1,498,045
U.S. Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,729	11,631
Gross Unrealized Gains	119	142
Gross Unrealized Losses	(4)	(3)
Estimated Fair Value	10,844	11,770
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,049	16,459
Gross Unrealized Gains	9	13
Gross Unrealized Losses	(1,795)	(1,677)
Estimated Fair Value	14,263	14,795
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,100	10,108
Gross Unrealized Gains	7	16
Gross Unrealized Losses	(137)	(114)
Estimated Fair Value	9,970	10,010
Asset backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,440	12,794
Gross Unrealized Losses	(188)	(282)
Estimated Fair Value	11,252	12,512
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,163	8,163
Gross Unrealized Losses	(1,351)	(1,390)
Estimated Fair Value	$ 6,812	$ 6,773