Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Amortized Cost
Due in one year	$ 7,601
Due after one year through five years	131,657
Due after five years through ten years	341,925
Due after ten years	1,727,147
Amortized Cost	2,208,330	$ 1,395,081
Estimated Fair Value
Due in one year	7,645
Due after one year through five years	130,955
Due after five years through ten years	342,606
Due after ten years	1,726,732
Totals	2,207,938	1,414,264
Amortized Cost
Due in one year	0
Due after one year through five years	1,766
Due after five years through ten years	16,612
Due after ten years	181,381
Amortized Cost	199,759	284,563
Estimated Fair Value
Due in one year	0
Due after one year through five years	1,890
Due after five years through ten years	17,090
Due after ten years	189,160
Totals	$ 208,140	$ 298,726