Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,127,048	$ 1,253,968
Gross Unrealized Gains	784	83
Gross Unrealized Losses	(23,789)	(43,134)
Estimated Fair Value	1,104,043	1,210,917
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,091,549	1,216,258
Gross Unrealized Gains	699	0
Gross Unrealized Losses	(21,223)	(40,249)
Estimated Fair Value	1,071,025	1,176,009
U.S. Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,432	8,170
Gross Unrealized Gains	74	68
Gross Unrealized Losses	(5)	(6)
Estimated Fair Value	7,501	8,232
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,030	14,807
Gross Unrealized Gains	9	9
Gross Unrealized Losses	(1,469)	(1,772)
Estimated Fair Value	12,570	13,044
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,874	6,570
Gross Unrealized Gains	2	6
Gross Unrealized Losses	(127)	(140)
Estimated Fair Value	5,749	6,436
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,163	8,163
Gross Unrealized Losses	(965)	(967)
Estimated Fair Value	$ 7,198	$ 7,196