Securities - Carrying Value and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Due within one year	$ 281,764
Due after one year through five years	1,758,382
Due after five years through ten years	2,167,043
Due after ten years	822,935
Total	5,030,124
Available-for-Sale, Estimated Fair Value, Due within one year	278,517
Available-for-Sale, Estimated Fair Value, Due after one year through five years	1,662,649
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	1,955,247
Available-for-Sale, Estimated Fair Value, Due after ten years	715,886
Available-for-Sale, Estimated Fair Value, Total	$ 4,612,299	$ 4,732,762	$ 4,652,537