Investment Securities - Contractual Maturities of Debt Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Due in one year, Amortized Cost	$ 67,436
Due after one year through five years, Amortized Cost	51,163
Due after five years through ten years, Amortized Cost	338,008
Due after ten years, Amortized Cost	335,853
Residential mortgage-backed securities, Amortized Cost	1,020,852
Total investment securities held to maturity, Amortized Cost	1,813,312	1,731,737
Due in one year, Fair Value	67,471
Due after one year through five years, Fair Value	56,054
Due after five years through ten years, Fair Value	355,791
Due after ten years, Fair Value	334,914
Residential mortgage-backed securities, Fair Value	1,024,402
Fair Value	$ 1,838,632	$ 1,711,427