Securities - Carrying Value and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Total	$ 5,253,099	$ 5,155,305	$ 5,217,517
Due within one year	279,646
Due after one year through five years	1,868,240
Due after five years through ten years	1,795,546
Due after ten years	1,309,667
Total	5,253,099
Available-for-Sale, Estimated Fair Value, Due within one year	276,226
Available-for-Sale, Estimated Fair Value, Due after one year through five years	1,754,031
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	1,608,902
Available-for-Sale, Estimated Fair Value, Due after ten years	1,121,272
Available-for-Sale, Estimated Fair Value, Total	$ 4,760,431	$ 4,617,759	$ 4,658,526