| **Loans (Troubled Debt Restructuring) (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended |
|---------------------------------------------------------------------------------------------------|----------------|
||
| **Financing Receivable, Modifications [Line Items]**                                              |           |   |
| Number of loans                                                                                   | 5              | 11 |
| Pre-modification outstanding recorded investment                                                  | $ 2,928        | $ 426 |
| Post-modification outstanding recorded investment                                                 | 2,580          | 426 |
| Commercial and agricultural [Member]                                                              |           |   |
| **Financing Receivable, Modifications [Line Items]**                                              |           |   |
| Number of loans                                                                                   | 0              | 0 |
| Pre-modification outstanding recorded investment                                                  | 0              | 0 |
| Post-modification outstanding recorded investment                                                 | 0              | 0 |
| Real estate - construction [Member]                                                               |           |   |
| **Financing Receivable, Modifications [Line Items]**                                              |           |   |
| Number of loans                                                                                   | 0              | 2 |
| Pre-modification outstanding recorded investment                                                  | 0              | 192 |
| Post-modification outstanding recorded investment                                                 | 0              | 192 |
| Real estate - mortgage, 1-4 family residential [Member]                                           |           |   |
| **Financing Receivable, Modifications [Line Items]**                                              |           |   |
| Number of loans                                                                                   | 4              | 8 |
| Pre-modification outstanding recorded investment                                                  | 1,777          | 210 |
| Post-modification outstanding recorded investment                                                 | 1,773          | 210 |
| Real estate - mortgage, commercial [Member]                                                       |           |   |
| **Financing Receivable, Modifications [Line Items]**                                              |           |   |
| Number of loans                                                                                   | 1              | 0 |
| Pre-modification outstanding recorded investment                                                  | 1,151          | 0 |
| Post-modification outstanding recorded investment                                                 | 807            | 0 |
| Consumer [Member]                                                                                 |           |   |
| **Financing Receivable, Modifications [Line Items]**                                              |           |   |
| Number of loans                                                                                   | 0              | 1 |
| Pre-modification outstanding recorded investment                                                  | 0              | 24 |
| Post-modification outstanding recorded investment                                                 | $ 0            | $ 24 |

| X                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of financing receivables that have been modified by troubled debt restructurings.
+ References
No definition available.
+ Details**Name:**fnbn_FinancingReceivableModificationsNumberOfContractsAlt**Namespace Prefix:**fnbn_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in financing receivables (after modification) modified by troubled debt restructurings.
+ References
No definition available.
+ Details**Name:**fnbn_FinancingReceivableModificationsPostModificationRecordedInvestmentAlt**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in financing receivables (before modification) modified by troubled debt restructurings.
+ References
No definition available.
+ Details**Name:**fnbn_FinancingReceivableModificationsPreModificationRecordedInvestmentAlt**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableModificationsLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |