Investment Securities - Contractual Maturities of Debt Securities Held to Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost
Due in one year	$ 85,139
Due after one year through five years	191,207
Due after five years through ten years	364,471
Due after ten years	172,295
Residential mortgage-backed securities	1,112,460
Amortized Cost	1,925,572	$ 1,596,385
Fair Value
Due in one year	85,139
Due after one year through five years	199,327
Due after five years through ten years	377,665
Due after ten years	159,664
Residential mortgage-backed securities	1,102,802
Total investment securities held to maturity	$ 1,924,597	$ 1,621,039