Investment Securities - Contractual Maturities of Debt Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Due in one year, Amortized Cost	$ 133,726
Due after one year through five years, Amortized Cost	43,702
Due after five years through ten years, Amortized Cost	254,295
Due after ten years, Amortized Cost	346,479
Residential mortgage-backed securities, Amortized Cost	925,577
Total investment securities held to maturity, Amortized Cost	1,703,779	1,599,707
Due in one year, Fair Value	134,039
Due after one year through five years, Fair Value	48,325
Due after five years through ten years, Fair Value	266,007
Due after ten years, Fair Value	331,041
Residential mortgage-backed securities, Fair Value	922,080
Fair Value	$ 1,701,492	$ 1,657,950