Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 261,110
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	3,087,180
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	2,771,160
Available-for-Sale, Amortized Cost Basis, Due after ten years	328,060
Available-for-Sale, Amortized Cost Basis, Total	6,447,510	$ 4,177,179
Available-for-Sale, Estimated Fair Value, Due within one year	264,173
Available-for-Sale, Estimated Fair Value, Due after one year through five years	3,150,010
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	2,831,581
Available-for-Sale, Estimated Fair Value, Due after ten years	327,415
Securities available-for-sale, Estimated Fair Value, Total	$ 6,573,179	$ 4,393,029