| **Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Detail) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2012 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|
| **Schedule of Available for sale Securities and Held to maturity Securities [Line Items]**                                                                                                                  |          |
| Due in one year or less                                                                                                                                                                                     | $ 4,366       |
| Due after one through five years                                                                                                                                                                            | 14,764        |
| Due after five through ten years                                                                                                                                                                            | 54,148        |
| Due after ten years                                                                                                                                                                                         | 85,489        |
| Available-For-Sale Securities, Debt Maturity, with Single Maturity Date, Amortized Cost, Total                                                                                                              | 158,767       |
| Total Investment Securities                                                                                                                                                                                 | 498,104       |
| Due in one year or less                                                                                                                                                                                     | 4,415         |
| Due after one through five years                                                                                                                                                                            | 15,468        |
| Due after five through ten years                                                                                                                                                                            | 57,442        |
| Due after ten years                                                                                                                                                                                         | 85,733        |
| Available-For-Sale Securities, Debt Maturity, with Single Maturity Date, Fair Value, Total                                                                                                                  | 163,058       |
| Total Investment Securities                                                                                                                                                                                 | 513,343       |
| Due in one year or less                                                                                                                                                                                     | 2,590         |
| Due after one through five years                                                                                                                                                                            | 2,554         |
| Due after five through ten years                                                                                                                                                                            | 57,811        |
| Due after ten years                                                                                                                                                                                         | 54,272        |
| Held-To-Maturity Securities, Debt Maturities, with Single Maturity Date, Net Carrying Amount, Total                                                                                                         | 117,227       |
| Total Investment Securities                                                                                                                                                                                 | 361,020       |
| Due in one year or less                                                                                                                                                                                     | 2,594         |
| Due after one through five years                                                                                                                                                                            | 2,575         |
| Due after five through ten years                                                                                                                                                                            | 60,163        |
| Due after ten years                                                                                                                                                                                         | 57,383        |
| Held-To-Maturity Securities, Debt Maturity, with Single Maturity Date, Fair Value, Total                                                                                                                    | 122,715       |
| Total Investment Securities                                                                                                                                                                                 | 378,174       |
| U.S. Government-sponsored mortgage-backed securities                                                                                                                                                        |          |
| **Schedule of Available for sale Securities and Held to maturity Securities [Line Items]**                                                                                                                  |          |
| Without single maturity date                                                                                                                                                                                | 337,631       |
| Without single maturity date                                                                                                                                                                                | 348,579       |
| Without single maturity date                                                                                                                                                                                | 243,793       |
| Without single maturity date                                                                                                                                                                                | 255,459       |
| Equity securities                                                                                                                                                                                           |          |
| **Schedule of Available for sale Securities and Held to maturity Securities [Line Items]**                                                                                                                  |          |
| Without single maturity date                                                                                                                                                                                | 1,706         |
| Without single maturity date                                                                                                                                                                                | 1,706         |
| Without single maturity date                                                                                                                                                                                |     |
| Without single maturity date                                                                                                                                                                                |     |

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| - Definition
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 rolling twelve months following the latest balance sheet presented.
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| - Definition
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 rolling twelve months following the latest balance sheet presented.
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| - Definition
Amount of available-for-sale debt securities at cost, net of adjustments, which include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.
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Amount of available-for-sale debt securities at cost, net of adjustments, maturing after the tenth rolling twelve months following the latest balance sheet presented. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.
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| - Definition
Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the sixth rolling twelve months through the tenth rolling twelve months following the latest balance sheet presented. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.
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Amount of available-for-sale debt securities at fair value maturing in the sixth rolling twelve months through the tenth rolling twelve months following the latest balance sheet presented.
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| - Definition
Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the second rolling twelve months through the fifth rolling twelve months following the latest balance sheet presented. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.
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Amount of available-for-sale debt securities at fair value maturing in the second rolling twelve months through the fifth rolling twelve months following the latest balance sheet presented.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of available-for-sale debt securities at cost, net of adjustments, that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the cost over several maturity groupings. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.
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| - Definition
Amount of available-for-sale debt securities at fair value that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the fair value over several maturity groupings.
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| - Definition
Amount of debt securities categorized neither as held-to-maturity nor trading.
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| - Definition
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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| - Definition
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.
+ References
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Amount of held-to-maturity debt securities at fair value maturing in the next rolling twelve months following the latest balance sheet presented.
+ References
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Amount of held-to-maturity debt securities at fair value maturing after the tenth rolling twelve months following the latest balance sheet presented.
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Amount of held-to-maturity debt securities at fair value maturing in the sixth rolling twelve months through the tenth rolling twelve months following the latest balance sheet presented.
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No definition available.
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Amount of held-to-maturity debt securities at fair value maturing in the second rolling twelve months through the fifth rolling twelve months following the latest balance sheet presented.
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| - Definition
Amount of held-to-maturity debt securities at fair value that do not have a single maturity date and which the entity has decided to disclose separately rather than allocating the fair value over several maturity groupings.
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| - Definition
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, over several maturity groupings.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 20 -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 Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (d),(f) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27232-111563
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