Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 326,804
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	1,487,053
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	2,817,340
Available-for-Sale, Amortized Cost Basis, Due after ten years	1,056,155
Available-for-Sale, Amortized Cost Basis, Total	5,687,352	$ 6,152,348	$ 6,722,336
Available-for-Sale, Estimated Fair Value, Due within one year	320,734
Available-for-Sale, Estimated Fair Value, Due after one year through five years	1,379,040
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	2,473,140
Available-for-Sale, Estimated Fair Value, Due after ten years	893,348
Securities available-for-sale, Estimated Fair Value, Total	$ 5,066,262	$ 5,474,359	$ 6,215,036