Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 267,375
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	1,499,938
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	3,126,228
Available-for-Sale, Amortized Cost Basis, Due after ten years	985,499
Available-for-Sale, Amortized Cost Basis, Total	5,879,040	$ 6,152,348	$ 6,767,967
Available-for-Sale, Estimated Fair Value, Due within one year	264,338
Available-for-Sale, Estimated Fair Value, Due after one year through five years	1,420,069
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	2,771,041
Available-for-Sale, Estimated Fair Value, Due after ten years	843,109
Securities available-for-sale, Estimated Fair Value, Total	$ 5,298,557	$ 5,474,359	$ 6,502,495