| **Loans and Allowance for Loan Losses (Details) (USD $)**                                      | 12 Months Ended |               |
|------------------------------------------------------------------------------------------------|-----------------|---------------|
||
| **Financing Receivable [Line Items]**                                                          |            |          |   |
| Loan charge-offs                                                                               | $ 30,968,000    | $ 128,424,000 |   |
| Recoveries of loan charge-offs                                                                 | 6,873,000       | 6,735,000     |   |
| Net loan charge-offs                                                                           | 24,100,000      |          |   |
| Ratio of Allowance for loan losses to loans held for investment                                | 2.49%           | 3.23%         | 7.18% |
| Real estate - mortgage, 1-4 family residential [Member] | PC [Member]                          |            |          |   |
| **Financing Receivable [Line Items]**                                                          |            |          |   |
| Loans purchases                                                                                | 137,400,000     |          |   |
| Loans purchases premium                                                                        | 3,700,000       |          |   |
| Granite Corp. [Member] | Real estate - mortgage, 1-4 family residential [Member] | PC [Member] |            |          |   |
| **Financing Receivable [Line Items]**                                                          |            |          |   |
| Loans purchases                                                                                | 35,800,000      |          |   |
| Loans purchases premium                                                                        | $ 300,000       |          |   |

| X                                                                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing Receivable, Allowance for Credit Losses, Write-downs Net of Recoveries
+ References
No definition available.
+ Details**Name:**fnbn_FinancingReceivableAllowanceForCreditLossesWriteDownsNetOfRecoveries**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Purchased principal amount of loans and leases receivable during the period.
+ References
No definition available.
+ Details**Name:**fnbn_LoansAndLeasesReceivablePurchases**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Premium amount related to the purchased loans and leases receivable during the period.
+ References
No definition available.
+ Details**Name:**fnbn_LoansAndLeasesReceivablePurchasesPremium**Namespace Prefix:**fnbn_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Allowance for loan and lease losses to loans and leases receivables ratio.
+ References
No definition available.
+ Details**Name:**fnbn_LoansAndLeasesReceivableRatioAllowanceForLoanAndLeaseLossesToLoansAndLeasesReceivables**Namespace Prefix:**fnbn_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of recovery of financing receivables doubtful of collection that were previously charged off.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953423-111524
+ Details**Name:**us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of direct write-downs of financing receivables charged against the allowance.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953423-111524
+ Details**Name:**us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |