Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 360,853
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	1,399,375
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	2,751,006
Available-for-Sale, Amortized Cost Basis, Due after ten years	732,447
Available-for-Sale, Amortized Cost Basis, Total	5,243,681	$ 6,152,348
Available-for-Sale, Estimated Fair Value, Due within one year	355,802
Available-for-Sale, Estimated Fair Value, Due after one year through five years	1,308,406
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	2,455,882
Available-for-Sale, Estimated Fair Value, Due after ten years	612,672
Securities available-for-sale, Estimated Fair Value, Total	$ 4,732,762	$ 5,474,359