Interest-bearing Time Deposits in Banks and Securities - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014
Investments Debt And Equity Securities [Abstract]
Available-for-Sale, Amortized Cost Basis, Due within one year	$ 67,059
Available-for-Sale, Amortized Cost Basis, Due after one year through five years	601,773
Available-for-Sale, Amortized Cost Basis, Due after five years through ten years	564,911
Available-for-Sale, Amortized Cost Basis, Due after ten years	9,786
Available-for-Sale, Amortized Cost Basis, Mortgage-backed securities	869,515
Available-for-Sale, Amortized Cost Basis, Total	2,113,044
Available-for-Sale, Estimated Fair Value, Due within one year	67,834
Available-for-Sale, Estimated Fair Value, Due after one year through five years	630,061
Available-for-Sale, Estimated Fair Value, Due after five years through ten years	586,752
Available-for-Sale, Estimated Fair Value, Due after ten years	10,868
Available-for-Sale, Estimated Fair Value, Mortgage-backed securities	878,313
Available-for-Sale, Estimated Fair Value, Total	$ 2,173,828