| **Investment Securities - Investments in Debt and Equity Securities Reported Less than Historical Cost (Detail) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2012 | Dec. 31, 2011 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Schedule of Investments [Line Items]**                                                                                                                          |          |          |
| Fair value                                                                                                                                                        | $ 17,038      | $ 6,339       |
| Investments in Debt and Equity Securities, Reported at Less than Historical Cost                                                                                  |          |          |
| **Schedule of Investments [Line Items]**                                                                                                                          |          |          |
| Historical cost                                                                                                                                                   | 22,999        | 11,925        |
| Fair value                                                                                                                                                        | $ 17,038      | $ 6,339       |
| Percent of the Corporation's available for sale and held to maturity portfolio                                                                                    | 1.90%         | 0.70%         |

| X                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Investment Historical Cost
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of Total Investment Portfolio, Fair Value
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Securities, Continuous Unrealized Loss Position, Fair Value
+ References
No definition available.
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| X                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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