| **Other Real Estate Owned and Property Acquired in Settlement of Loans (Tables)** | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|-----------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Repossessed Assets [Abstract]**                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| Schedule of Repossessed Assets                                                    | The following table summarizes OREO and personal property acquired in settlement of loans at the periods indicated:(dollars in thousands) March 31, 2013 December 31, 2012Real estate acquired in settlement of loans $46,307 $62,796Personal property acquired in settlement of loans 230 335Total property acquired in settlement of loans $46,537 $63,131                                                                                                                                                                                                                                                      |
| Activities of Real Estate Acquired through Foreclosure                            | The following tables summarize the changes in real estate acquired in settlement of loans at the periods indicated:  For Three Months Ended(dollars in thousands) March 31, 2013 March 31, 2012Real estate acquired in settlement of loans, beginning of period $62,796 $110,009Plus:  New real estate acquired in settlement of loans 3,969 8,935Less:  Sales of real estate acquired in settlement of loans (20,239) (10,874)Less:  Write-downs and net loss on sales charged to expense (219) (3,877)Real estate acquired in settlement of loans, end of period $46,307 $104,193 |

| X                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of the change in real estate assets taken in settlement of troubled loans through surrender or foreclosure.
+ References
No definition available.
+ Details**Name:**fnbn_ActivitiesOfRealEstateAcquiredThroughForeclosureTableTextBlock**Namespace Prefix:**fnbn_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of real estate and personal property taken in settlement of troubled loans through surrender or foreclosure.
+ References
No definition available.
+ Details**Name:**fnbn_ScheduleOfRepossessedAssetsTableTextBlock**Namespace Prefix:**fnbn_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_ForeclosedAssetsAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |