| **Investment Securities - Investments' Gross Unrealized Losses and Fair Value Aggregated by Investment Category and Length of Time in Continuous Unrealized Loss Position (Detail) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2012 | Dec. 31, 2011 |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Investments, Unrealized Loss Position [Line Items]**                                                                                                                                                                               |          |          |
| Less than 12 Months Fair Value                                                                                                                                                                                                       | $ 16,844      | $ 6,176       |
| Less than 12 Months Gross Unrealized Losses                                                                                                                                                                                          | 80            | 16            |
| 12 Months or Longer Fair Value                                                                                                                                                                                                       | 194           | 163           |
| 12 Months or Longer Gross Unrealized Losses                                                                                                                                                                                          | 5,881         | 5,572         |
| Total Fair Value                                                                                                                                                                                                                     | 17,038        | 6,339         |
| Total Gross Unrealized Losses                                                                                                                                                                                                        | 5,961         | 5,588         |
| State and municipal                                                                                                                                                                                                                  |          |          |
| **Investments, Unrealized Loss Position [Line Items]**                                                                                                                                                                               |          |          |
| Less than 12 Months Fair Value                                                                                                                                                                                                       | 4,524         |          |
| Less than 12 Months Gross Unrealized Losses                                                                                                                                                                                          | 19            |          |
| 12 Months or Longer Fair Value                                                                                                                                                                                                       |     |          |
| 12 Months or Longer Gross Unrealized Losses                                                                                                                                                                                          |     |          |
| Total Fair Value                                                                                                                                                                                                                     | 4,524         |          |
| Total Gross Unrealized Losses                                                                                                                                                                                                        | 19            |          |
| U.S. Government-sponsored mortgage-backed securities                                                                                                                                                                                 |          |          |
| **Investments, Unrealized Loss Position [Line Items]**                                                                                                                                                                               |          |          |
| Less than 12 Months Fair Value                                                                                                                                                                                                       | 12,320        | 6,176         |
| Less than 12 Months Gross Unrealized Losses                                                                                                                                                                                          | 61            | 16            |
| 12 Months or Longer Fair Value                                                                                                                                                                                                       |     |     |
| 12 Months or Longer Gross Unrealized Losses                                                                                                                                                                                          |     |     |
| Total Fair Value                                                                                                                                                                                                                     | 12,320        | 6,176         |
| Total Gross Unrealized Losses                                                                                                                                                                                                        | 61            | 16            |
| Corporate Bonds and Notes                                                                                                                                                                                                            |          |          |
| **Investments, Unrealized Loss Position [Line Items]**                                                                                                                                                                               |          |          |
| Less than 12 Months Fair Value                                                                                                                                                                                                       |     |     |
| Less than 12 Months Gross Unrealized Losses                                                                                                                                                                                          |     |     |
| 12 Months or Longer Fair Value                                                                                                                                                                                                       | 194           | 163           |
| 12 Months or Longer Gross Unrealized Losses                                                                                                                                                                                          | 5,881         | 5,572         |
| Total Fair Value                                                                                                                                                                                                                     | 194           | 163           |
| Total Gross Unrealized Losses                                                                                                                                                                                                        | $ 5,881       | $ 5,572       |

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