| **Intangible Assets (Details Textual) (USD $)**                                    | 12 Months Ended | 0 Months Ended |
|------------------------------------------------------------------------------------|-----------------|----------------|
||
| **Finite-Lived Intangible Assets [Line Items]**                                    |            |           |   |   |
| Amortization of core deposit premiums                                              | $ 1,407,000     | $ 896,000      | $ 795,000 |   |
| Unpaid principal balance of mortgage loans serviced for others (unconsolidated)    | 65,100,000      | 2,000,000      | 493,700,000 |   |
| Servicing Assets, Unconsolidated Mortgage Loans Serviced, Unpaid Principal Balance |            | 700,000        |   |   |
| Sale of Mortgage Servicing Rights (MSR)                                            |            |           |   | 492,900,000 |
| Loss on sale of Mortgage Servicing Rights (MSR)                                    |            |           |   | $ 3,000,000 |

| X                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Gain (Loss) on Sale of Mortgage Servicing Rights (MSR)
+ References
No definition available.
+ Details**Name:**fnbn_GainLossOnSaleOfMortgageServicingRightsMsr**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Sale of Mortgage Servicing Rights (MSR)
+ References
No definition available.
+ Details**Name:**fnbn_SaleOfMortgageServicingRightsMsr**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This represents the unpaid principal balance of the unconsolidated loans serviced under the servicing contract.
+ References
No definition available.
+ Details**Name:**fnbn_ServicingAssetsUnconsolidatedLoansServicedUnpaidPrincipalBalance**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Servicing Assets, Unconsolidated Mortgage Loans Serviced, Unpaid Principal Balance
+ References
No definition available.
+ Details**Name:**fnbn_ServicingAssetsUnconsolidatedMortgageLoansServicedUnpaidPrincipalBalance**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275
+ Details**Name:**us-gaap_AmortizationOfIntangibleAssets**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FiniteLivedIntangibleAssetsLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |