| **Valuation Methodologies Used for Instruments Measured at Fair Value on Non-Recurring Basis (Detail) (Fair Value, Measurements, Nonrecurring, USD $)In Thousands, unless otherwise specified** | Mar. 31, 2013 | Dec. 31, 2012 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Impaired Loans                                                                                                                                                                                  |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                |          |          |
| Asset fair value                                                                                                                                                                                | $ 11,096      | $ 17,703      |
| Other Real Estate Owned                                                                                                                                                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                |          |          |
| Asset fair value                                                                                                                                                                                | 4,411         | 7,684         |
| Significant Unobservable Inputs (Level 3) | Impaired Loans                                                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                |          |          |
| Asset fair value                                                                                                                                                                                | 11,096        | 17,703        |
| Significant Unobservable Inputs (Level 3) | Other Real Estate Owned                                                                                                                             |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                                                |          |          |
| Asset fair value                                                                                                                                                                                | $ 4,411       | $ 7,684       |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258
+ Details**Name:**us-gaap_AssetsFairValueDisclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |