| **Fair Values of Financial Instruments - Transfer Between Levels 1, 2 and 3 and Reasons For Those Transfers (Detail) (USD $)In Thousands, unless otherwise specified** | 12 Months Ended                                                                                                                                                                                                                                                         |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| Available-for-sale securities                                                                                                                                          |                                                                                                                                                                                                                                                                    |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                       |                                                                                                                                                                                                                                                                    |
| Reason for Transfer                                                                                                                                                    | Selected state and municipal securities were transferred from Level 2 to Level 3 due to limited availability of similar securities in active markets.                                                                                                                   |
| Held to Maturity Securities                                                                                                                                            |                                                                                                                                                                                                                                                                    |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                       |                                                                                                                                                                                                                                                                    |
| Reason for Transfer                                                                                                                                                    | Selected state and municipal securities were transferred from available for sale to held to maturity.  These securities are valued at amortized cost and are no longer classified within the fair value hierarchy.                                                      |
| Significant Other Observable Inputs (Level 2) | Available-for-sale securities                                                                                          |                                                                                                                                                                                                                                                                    |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                       |                                                                                                                                                                                                                                                                    |
| Transfer between Levels 1, 2 and 3                                                                                                                                     | (350)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet/ us-gaap_FairValueByAssetClassAxis= us-gaap_AvailableforsaleSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member  |
| Significant Other Observable Inputs (Level 2) | Held to Maturity Securities                                                                                            |                                                                                                                                                                                                                                                                    |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                       |                                                                                                                                                                                                                                                                    |
| Transfer between Levels 1, 2 and 3                                                                                                                                     |                                                                                                                                                                                                                                                               |
| Significant Unobservable Inputs (Level 3) | Available-for-sale securities                                                                                              |                                                                                                                                                                                                                                                                    |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                       |                                                                                                                                                                                                                                                                    |
| Transfer between Levels 1, 2 and 3                                                                                                                                     | 350us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet/ us-gaap_FairValueByAssetClassAxis= us-gaap_AvailableforsaleSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member    |
| Significant Unobservable Inputs (Level 3) | Held to Maturity Securities                                                                                                |                                                                                                                                                                                                                                                                    |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                                                       |                                                                                                                                                                                                                                                                    |
| Transfer between Levels 1, 2 and 3                                                                                                                                     | (16,784)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet/ us-gaap_FairValueByAssetClassAxis= us-gaap_HeldtomaturitySecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member |

| X                                                                                                                                                                                                                 |
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
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| - Definition
Disclosures concerning the reasons for transfers out of Level 3 of the fair value hierarchy.
+ 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 (c)(3) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258
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| X                                                                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.
+ References
No definition available.
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| X                                                                                                                                                                          |
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| X                                                                                                                                                                          |
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