| **Employee Benefit Plans (Matching Retirement/Savings Plan) (Details) (USD $)**                           | 12 Months Ended |
|-----------------------------------------------------------------------------------------------------------|-----------------|
||
| **Defined Contribution Pension and Other Postretirement Plans Disclosure [Line Items]**                   |            |   |   |
| Employer matching contribution percentage                                                                 | 50.00%          |   |   |
| Percentage of pay deferred by employee eligible for employer matching contributions                       | 6.00%           |   |   |
| Matching and discretionary contributions                                                                  | $ 600,000       | $ 400,000 | $ 500,000 |
| FNB Matching Retirement/Savings Plan [Member]                                                             |            |   |   |
| **Defined Contribution Pension and Other Postretirement Plans Disclosure [Line Items]**                   |            |   |   |
| Employer matching contribution percentage                                                                 | 50.00%          |   |   |
| Percentage of pay deferred by employee eligible for employer matching contributions                       | 6.00%           |   |   |
| Discretionary contributions                                                                               | 0               | 0 | 0 |
| Matching and discretionary contributions                                                                  | 600,000         | 400,000 | 500,000 |
| Tax-Qualified Profit-Sharing and Savings Retirement Plan [Member] | Granite Corp. [Member]                |            |   |   |
| **Defined Contribution Pension and Other Postretirement Plans Disclosure [Line Items]**                   |            |   |   |
| Employer matching contribution percentage                                                                 | 50.00%          |   |   |
| Percentage of pay deferred by employee eligible for employer matching contributions                       | 6.00%           |   |   |
| Matching and discretionary contributions                                                                  | 0               | 0 |   |
| Non-Tax Qualified Profit-Sharing Supplemental Executive Retirement Plan [Member] | Granite Corp. [Member] |            |   |   |
| **Defined Contribution Pension and Other Postretirement Plans Disclosure [Line Items]**                   |            |   |   |
| Matching and discretionary contributions                                                                  | 0               | 0 |   |
| Future obligations under plan                                                                             | $ 0             | $ 0 |   |

| X                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**fnbn_DefinedContributionPensionAndOtherPostretirementPlansDisclosureLineItems**Namespace Prefix:**fnbn_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage employer matches of the employee's percentage contribution matched.
+ References
No definition available.
+ Details**Name:**fnbn_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch**Namespace Prefix:**fnbn_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.
+ References
No definition available.
+ Details**Name:**us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of the cost recognized during the period for defined contribution plans.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 11 -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.
+ Details**Name:**us-gaap_DefinedContributionPlanCostRecognized**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of discretionary contributions made by an employer to a defined contribution plan.
+ References
No definition available.
+ Details**Name:**us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.
+ References
No definition available.
+ Details**Name:**us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |