Investment Securities - Contractual Maturities of Debt Securities Held to Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Due in one year, Amortized Cost	$ 77,803
Due after one year through five years, Amortized Cost	145,649
Due after five years through ten years, Amortized Cost	314,175
Due after ten years, Amortized Cost	206,469
Residential mortgage-backed securities, Amortized Cost	852,289
Amortized Cost	1,596,385	$ 1,778,316
Due in one year, Fair Value	77,803
Due after one year through five years, Fair Value	154,897
Due after five years through ten years, Fair Value	332,505
Due after ten years, Fair Value	200,562
Residential mortgage-backed securities, Fair Value	855,272
Fair Value	$ 1,621,039	$ 1,815,976