Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 292,438
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	1,815,382
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	2,073,461
Available-for-Sale, Amortized Cost Basis, Due after ten years	974,024
Available-for-Sale, Amortized Cost Basis, Total	5,155,305	$ 5,243,681
Available-for-Sale, Estimated Fair Value, Due within one year	288,985
Available-for-Sale, Estimated Fair Value, Due after one year through five years	1,678,422
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	1,821,254
Available-for-Sale, Estimated Fair Value, Due after ten years	829,098
Securities available-for-sale, Estimated Fair Value, Total	$ 4,617,759	$ 4,732,762