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, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 206,182
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	664,151
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	836,421
Available-for-Sale, Amortized Cost Basis, Due after ten years	3,360
Available-for-Sale, Amortized Cost Basis, Mortgage-backed securities	1,117,658
Available-for-Sale, Amortized Cost Basis, Total	2,827,772	$ 2,654,885
Available-for-Sale, Estimated Fair Value, Due within one year	207,276
Available-for-Sale, Estimated Fair Value, Due after one year through five years	684,849
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	845,257
Available-for-Sale, Estimated Fair Value, Due after ten years	3,658
Available-for-Sale, Estimated Fair Value, Mortgage-backed securities	1,119,797
Securities available-for-sale, Estimated Fair Value, Total	$ 2,860,837	$ 2,733,899