Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Amortized Cost
Due in one year	$ 14,470
Due after one year through five years	123,099
Due after five years through ten years	423,389
Due after ten years	2,254,209
Amortized Cost	2,815,167	$ 2,208,330
Estimated Fair Value
Due in one year	14,303
Due after one year through five years	118,336
Due after five years through ten years	409,143
Due after ten years	2,064,283
Totals	2,606,065	2,207,938
Amortized Cost
Due in one year	0
Due after one year through five years	1,645
Due after five years through ten years	13,742
Due after ten years	161,407
Totals	176,794	199,759
Estimated Fair Value
Due in one year	0
Due after one year through five years	1,655
Due after five years through ten years	13,605
Due after ten years	155,882
Totals	$ 171,142	$ 208,140