Interest-bearing Time Deposits in Banks and Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year		$ 187,600
Available-for-Sale, Amortized Cost Basis, Due after one year through five years		547,868
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years		507,792
Available-for-Sale, Amortized Cost Basis, Due after ten years		1,714
Available-for-Sale, Amortized Cost Basis, Mortgage-backed securities		1,908,594
Available-for-Sale, Amortized Cost Basis, Total	$ 3,153,568	3,153,568	$ 3,042,618
Available-for-Sale, Estimated Fair Value, Due within one year		188,914
Available-for-Sale, Estimated Fair Value, Due after one year through five years		563,679
Available-for-Sale, Estimated Fair Value, Due after five years through ten years		518,317
Available-for-Sale, Estimated Fair Value, Due after ten years		2,022
Available-for-Sale, Estimated Fair Value, Mortgage-backed securities		1,885,845
Securities available-for-sale, Estimated Fair Value, Total	$ 3,158,777	$ 3,158,777	$ 3,087,473