| **Basis of Presentation (Policies)** | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
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| **Accounting Policies [Abstract]**   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Use of Estimates                     | Use of EstimatesWe have made a number of estimates and assumptions relating to the reporting of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period to prepare these consolidated financial statements in conformity with accounting principles generally accepted in the United States ("GAAP").  Actual results could differ from those estimates.  Material estimates subject to change in the near term include, among other items, the allowances for loan losses (“ALL”), the carrying value of other real estate owned (“OREO”), the carrying value of intangible assets and the realization of deferred tax assets.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Reclassification                     | ReclassificationCertain reclassifications have been made to the prior period consolidated financial statements to place them on a comparable basis with the current period consolidated financial statements.  These reclassifications have no effect on net income or shareholders' equity as previously reported.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Subsequent Events                    | Subsequent EventsSubsequent events are events or transactions that occur after the balance sheet date but before financial statements are issued.  Recognized subsequent events are events or transactions that provide additional evidence about conditions that existed at the date of the balance sheet, including the estimates inherent in the process of preparing financial statements.  Non-recognized subsequent events are events that provide evidence about conditions that did not exist at the date of the balance sheet but arose after that date.  Management has reviewed events occurring through the date of this filing and has concluded that no subsequent events have occurred requiring accrual or disclosure in addition to that included herein.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Recent Accounting Pronouncements     | Recent Accounting PronouncementsComprehensive Income - In February 2013, the FASB issued ASU No. 2013-02 Comprehensive Income (Topic 220): Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income (“ASU No. 2013-02”). This pronouncement requires an entity to report the effect of significant reclassifications out of accumulated other comprehensive income for each applicable component of net income, as well as a rollforward of the components of accumulated other comprehensive income on a prospective basis. This pronouncement is effective beginning January 1, 2013. The provisions of ASU No. 2013-02 relate only to financial statement presentation of other comprehensive income and, accordingly, its adoption did not have a material effect on FNB's financial statements. See Note 10 for further disclosure.FASB - From time to time, the Financial Accountings Standards Board (“FASB”) issues exposure drafts for proposed statements of financial accounting standards. Such exposure drafts are subject to comment from the public, to revisions by the FASB and to final issuance by the FASB as statements of financial accounting standards. Management considers the effect of the proposed statements on the consolidated financial statements of FNB and monitors the status of changes to and proposed effective dates of exposure drafts. Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies are not expected to have a material impact on FNB’s financial position, results of operations or cash flows. |

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| - Definition
Disclosure of the adoption of new accounting pronouncements that may impact the entity's financial reporting.
+ References
No definition available.
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| - Definition
Disclosure of accounting policy for reclassifications that affects the comparability of the financial statements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6359566&loc=d3e326-107755
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| - Definition
Disclosure of accounting policy for reporting subsequent events.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367646&loc=d3e18780-107790
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| - Definition
Disclosure of accounting policy for the use of estimates in the preparation of financial statements in conformity with generally accepted accounting principles.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 94-6 -Paragraph 11, 14 -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 275 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6143-108592Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6132-108592Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6061-108592
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