Investment Securities - Contractual Maturities of Held to Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized Cost
Due in one year	$ 66,622
Due after one year through five years	220,086
Due after five years through ten years	338,507
Due after ten years	163,701
Residential mortgage-backed securities	1,113,413
Amortized Cost	1,902,329	$ 1,925,572
Fair Value
Due in one year	66,712
Due after one year through five years	229,218
Due after five years through ten years	353,152
Due after ten years	151,671
Residential mortgage-backed securities	1,103,770
Total investment securities held to maturity	$ 1,904,523	$ 1,924,597