| **Short-Term Borrowings and Long-Term Debt (Tables)**                | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
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| **Debt Disclosure [Abstract]**                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Schedule of FNB's Short-term and Long-term Borrowings                | The following table stratifies FNB’s borrowings as short-term and long-term at the periods indicated.   December 31,(dollars in thousands) 2012 2011  Balance Rate Balance RateShort-term borrowings:        Retail customer repurchase agreements $8,675 0.19% $8,838 0.42%Total short-term borrowings $8,675   $8,838  Long-term debt:        Federal Home Loan Bank advances $58,328 2.62 $58,370 2.63Junior subordinated debt 56,702 1.83 56,702 2.09Total long-term debt $115,030   $115,072                                                                                                                                         |
| Schedule of Retail Repurchase Agreements and Federal Funds Purchased | Information concerning retail repurchase agreements and federal funds purchased is as follows: (dollars in thousands) 2012 2011 2010  RetailRepurchaseAgreements  RetailRepurchaseAgreements  RetailRepurchaseAgreements FederalFundsPurchasedBalance at December 31 $8,675  $8,838  $9,628 $—Average balance during the year 9,861  8,973  13,355 1,537Maximum month end balance 12,720  10,917  16,424 15,000Weighted average interest rate:          At December 31 0.19%  0.42%  0.78% —%During the year 0.29  0.58  0.73 0.26                                                                                        |
| FHLB advance [Member]                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| **Debt Instrument [Line Items]**                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Scheduled Maturities of Long-term Debt                               | At December 31, 2012, the scheduled maturities of FHLB advances payable over the next five years and thereafter, certain of which are convertible to a variable rate at the option of the FHLB before scheduled maturity, are as follows:(dollars in thousands) Twelve Months Ended December 31, 2013$—20145,00020153,0002016—2017—2018 and thereafter50,328Total FHLB advances$58,328                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Schedule of Long-term Debt                                           | Long-term debt consisted of the following advances from the FHLB at the periods indicated. (dollars in thousands)          December 31,Maturity Interest Rate 2012 2011December 29, 2014 3.3125% $5,000 $5,000September 8, 2015 3.7100% 3,000 3,000March 19, 2018 2.8100% 10,000 10,000July 6, 2018 2.4300% 20,000 20,000July 18, 2018 2.3300% 20,000 20,000August 27, 2018 6.1500% 328 370    $58,328 $58,370                                                                                                                                                                                                                                                                |
| Junior Subordinated Debentures [Member]                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| **Debt Instrument [Line Items]**                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Schedule of Long-term Debt                                           | Information concerning the Junior Subordinated Debentures is as follows at the periods indicated. (dollars in thousands)   Commencement        Stated of Early As of December 31,   Maturity Redemption 20122011 Issuer Date Period PrincipalUnpaid InterestPrincipalUnpaid InterestInterest RateFNB Trust I 12/15/2035 12/15/2010 $20,619 $20,619 3 month LIBOR + 1.37% =1.676% at 12/31/12FNB Trust II 6/30/2036 6/30/2011 30,928 30,928 3 month LIBOR + 1.32% =1.626% at 12/31/12Catawba Trust II 12/30/2032 12/30/2007 5,155 5,155 3 month LIBOR + 3.35% =3.656% at 12/31/12Total Junior Subordinated Debentures     $56,702 $56,702   |

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| - Definition
Schedule of Repurchase Agreements, Resale Agreements, Securities Borrowed, and Securities Loaned [Table Text Block]
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| - Definition
Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.
+ References
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| - Definition
Tabular disclosure of information pertaining to short-term and long-debt instruments or arrangements, including but not limited to identification of terms, features, collateral requirements and other information necessary to a fair presentation.
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| - Definition
Tabular disclosure of the combined aggregate amount of maturities and sinking fund requirements for all long-term borrowings for each of the five years following the date of the latest balance sheet date presented.
+ References
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