Securities - Amortized Cost and Fair Value of Held to Maturity Securities by Final Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investments Debt And Equity Securities [Abstract]
Securities Held to Maturity, Due in one year or less, Amortized Cost	$ 4,736
Securities Held to Maturity, Due after one year through five years, Amortized Cost	651,155
Securities Held to Maturity, Due after five years through ten years, Amortized Cost	126,510
Securities Held to Maturity, Due after ten years, Amortized Cost	1,644,534
Total Held to Maturity securities, Amortized Cost	2,426,935	2,611,352
Securities Held to Maturity, Due in one year or less, Fair Value	4,764
Securities Held to Maturity, Due after one year through five years, Fair Value	636,445
Securities Held to Maturity, Due after five years through ten years, Fair Value	124,267
Securities Held to Maturity, Due after ten years, Fair Value	1,652,403
Total Held to Maturity Securities, Fair Value	$ 2,417,879	$ 2,576,584