Securities - Amortized Cost and Fair Value of Held to Maturity Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Due in one year or less, Amortized Cost	$ 14,545
Securities Held to Maturity, Due after one year through five years, Amortized Cost	417,869
Securities Held to Maturity, Due after five years through ten years, Amortized Cost	94,584
Securities Held to Maturity, Due after ten years, Amortized Cost	1,141,020
Total Held to Maturity securities, Amortized Cost	1,668,018
Securities Held to Maturity, Due in one year or less, Fair Value	14,626
Securities Held to Maturity, Due after one year through five years, Fair Value	427,022
Securities Held to Maturity, Due after five years through ten years, Fair Value	104,739
Securities Held to Maturity, Due after ten years, Fair Value	1,164,078
Total Held to Maturity Securities, Fair Value	$ 1,710,465

Amount of held-to-maturity debt securities at fair value maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing in the fifth through tenth fiscal year following the latest fiscal year.

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Amount of held-to-maturity debt securities at fair value maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year.

+ References

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing in the next fiscal year through the fifth fiscal year following the latest fiscal year.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Amount of held-to-maturity debt securities at fair value maturing after the tenth fiscal year following the latest fiscal year.

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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing after the tenth fiscal year following the latest fiscal year.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized as held-to-maturity.

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Amount of held-to-maturity debt securities at fair value maturing in the next fiscal year following the latest fiscal year.

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