Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Amortized Cost
Due in one year	$ 57,662
Due after one year through five years	114,294
Due after five years through ten years	407,960
Due after ten years	2,081,741
Amortized Cost	2,661,657	$ 2,742,987
Estimated Fair Value
Due in one year	56,205
Due after one year through five years	109,745
Due after five years through ten years	389,802
Due after ten years	1,850,060
Totals	2,405,812	2,452,438
Amortized Cost
Due in one year	0
Due after one year through five years	5,316
Due after five years through ten years	9,592
Due after ten years	137,159
Totals	152,067	160,983
Estimated Fair Value
Due in one year	0
Due after one year through five years	5,157
Due after five years through ten years	9,081
Due after ten years	127,897
Totals	$ 142,135	$ 149,938