Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 239,974
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	2,213,010
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	2,394,729
Available-for-Sale, Amortized Cost Basis, Due after ten years	1,698,758
Available-for-Sale, Amortized Cost Basis, Total	6,546,471	$ 6,447,510	$ 5,981,374
Available-for-Sale, Estimated Fair Value, Due within one year	238,511
Available-for-Sale, Estimated Fair Value, Due after one year through five years	2,056,408
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	2,051,847
Available-for-Sale, Estimated Fair Value, Due after ten years	1,398,677
Securities available-for-sale, Estimated Fair Value, Total	$ 5,745,443	$ 6,573,179	$ 6,119,984