| **Impairment of Investment Securities - Schedule of Unrealized Losses and Estimated Fair Values (Detail) (USD $)** | Mar. 31, 2013 | Dec. 31, 2012 |
|--------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                           |          |               |   |  |
| Estimated Fair Value, Less Than 12 Months                                                                          | $ 313,008,000 |               | $ 135,599,000 |  |
| Gross Unrealized Losses Less Than 12 Months                                                                        | (2,296,000)   |               | (464,000) |  |
| Estimated Fair Value, 12 Months or More                                                                            | 24,487,000    |               | 23,350,000 |  |
| Gross Unrealized Losses 12 Months or More                                                                          | (26,566,000)  |               | (28,496,000) |  |
| Total Estimated Fair Value                                                                                         | 337,495,000   |               | 158,949,000 |  |
| Total Gross Unrealized Losses                                                                                      | 28,862,000    |               | 28,960,000 |  |
| Corporate Debt Securities [Member]                                                                                 |          |               |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                           |          |               |   |  |
| Estimated Fair Value, Less Than 12 Months                                                                          | 4,797,000     |               |   |  |
| Gross Unrealized Losses Less Than 12 Months                                                                        | (30,000)      |               |   |  |
| Estimated Fair Value, 12 Months or More                                                                            | 0             |               |   |  |
| Gross Unrealized Losses 12 Months or More                                                                          | 0             |               |   |  |
| Total Estimated Fair Value                                                                                         | 4,797,000     |               |   |  |
| Total Gross Unrealized Losses                                                                                      | 30,000        |               |   |  |
| Pooled Trust Preferred Collateralized Debt Obligations [Member]                                                    |          |               |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                           |          |               |   |  |
| Estimated Fair Value, Less Than 12 Months                                                                          | 0             |               | 0 |  |
| Gross Unrealized Losses Less Than 12 Months                                                                        | 0             |               | 0 |  |
| Estimated Fair Value, 12 Months or More                                                                            | 24,454,000    |               | 23,316,000 |  |
| Gross Unrealized Losses 12 Months or More                                                                          | (26,566,000)  |               | (28,496,000) |  |
| Total Estimated Fair Value                                                                                         | 24,454,000    |               | 23,316,000 |  |
| Total Gross Unrealized Losses                                                                                      | 26,566,000    |               | 28,496,000 |  |
| Obligations of U.S. Government Agencies [Member] | Mortgage Backed Securities - Residential [Member]               |          |               |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                           |          |               |   |  |
| Estimated Fair Value, Less Than 12 Months                                                                          | 0             |               | 0 |  |
| Gross Unrealized Losses Less Than 12 Months                                                                        | 0             |               | 0 |  |
| Estimated Fair Value, 12 Months or More                                                                            | 13,000        |               | 13,000 |  |
| Gross Unrealized Losses 12 Months or More                                                                          | 0             | [1]           | 0 | [1] |
| Total Estimated Fair Value                                                                                         | 13,000        |               | 13,000 |  |
| Total Gross Unrealized Losses                                                                                      | 0             |               | 0 |  |
| Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage Backed Securities - Residential [Member]  |          |               |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                           |          |               |   |  |
| Estimated Fair Value, Less Than 12 Months                                                                          | 248,747,000   |               | 76,296,000 |  |
| Gross Unrealized Losses Less Than 12 Months                                                                        | (2,153,000)   |               | (392,000) |  |
| Estimated Fair Value, 12 Months or More                                                                            | 20,000        |               | 21,000 |  |
| Gross Unrealized Losses 12 Months or More                                                                          | 0             | [1]           | 0 | [1] |
| Total Estimated Fair Value                                                                                         | 248,767,000   |               | 76,317,000 |  |
| Total Gross Unrealized Losses                                                                                      | 2,153,000     |               | 392,000 |  |
| Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government Sponsored Enterprises [Member]    |          |               |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                           |          |               |   |  |
| Estimated Fair Value, Less Than 12 Months                                                                          | 59,464,000    |               | 59,303,000 |  |
| Gross Unrealized Losses Less Than 12 Months                                                                        | (113,000)     |               | (72,000) |  |
| Estimated Fair Value, 12 Months or More                                                                            | 0             |               | 0 |  |
| Gross Unrealized Losses 12 Months or More                                                                          | 0             |               | 0 |  |
| Total Estimated Fair Value                                                                                         | 59,464,000    |               | 59,303,000 |  |
| Total Gross Unrealized Losses                                                                                      | $ 113,000     |               | $ 72,000 |  |
|                                                                                                                    |
| [1]Gross unrealized losses related to these types of securities are less than $1 thousand.                         |

| X                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Available-for-sale securities continuous unrealized income (loss) position less than twelve months aggregate gain (losses).
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities which are categorized neither as held-to-maturity nor trading securities.
+ References
No definition available.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of the excess of amortized cost basis over fair value of securities in a loss position and categorized neither as held-to-maturity nor trading securities.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.
+ References
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