Securities - Schedule of Amortized Cost, Fair Value and Gross Unrealized Gains and Losses for Securities Held to Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 5,626,437	$ 5,691,868
Gross Unrealized Gains	15,957	21,039
Gross Unrealized Losses	(617,256)	(529,540)
Held to Maturity, Fair value	5,025,138	5,183,367
Allowance for Credit Losses	(3,820)	(3,258)
Net Carrying Amount	5,622,617	5,688,610
U.S. Agencies [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	123,240	123,210
Gross Unrealized Losses	(2,661)	(2,686)
Held to Maturity, Fair value	120,579	120,524
Net Carrying Amount	123,240	123,210
Mortgage-backed [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	2,691,133	2,738,253
Gross Unrealized Gains		18
Gross Unrealized Losses	(404,520)	(356,657)
Held to Maturity, Fair value	2,286,613	2,381,614
Net Carrying Amount	2,691,133	2,738,253
State and political subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	2,812,064	2,830,405
Gross Unrealized Gains	15,957	21,021
Gross Unrealized Losses	(210,075)	(170,197)
Held to Maturity, Fair value	2,617,946	2,681,229
Allowance for Credit Losses	(3,820)	(3,258)
Net Carrying Amount	$ 2,808,244	$ 2,827,147