Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 239,670
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	2,912,498
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	2,925,448
Available-for-Sale, Amortized Cost Basis, Due after ten years	644,720
Available-for-Sale, Amortized Cost Basis, Total	6,722,336	$ 6,447,510	$ 5,405,189
Available-for-Sale, Estimated Fair Value, Due within one year	239,640
Available-for-Sale, Estimated Fair Value, Due after one year through five years	2,780,193
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	2,630,741
Available-for-Sale, Estimated Fair Value, Due after ten years	564,462
Securities available-for-sale, Estimated Fair Value, Total	$ 6,215,036	$ 6,573,179	$ 5,578,048

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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