Securities - Carrying Value and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024
Investments, Debt and Equity Securities [Abstract]
Total	$ 5,359,666	$ 5,155,305	$ 5,132,451
Due within one year	282,480
Due after one year through five years	2,103,481
Due after five years through ten years	1,631,680
Due after ten years	1,342,025
Total	5,359,666
Available-for-Sale, Estimated Fair Value, Due within one year	279,764
Available-for-Sale, Estimated Fair Value, Due after one year through five years	1,986,766
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	1,477,793
Available-for-Sale, Estimated Fair Value, Due after ten years	1,142,225
Available-for-Sale, Estimated Fair Value, Total	$ 4,886,548	$ 4,617,759	$ 4,573,024