|**Short-Term Borrowings and Long-Term Debt (Tables)**                | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
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|**Debt Instrument [Line Items]**                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Schedule of Short-term and Long-term Borrowings                      | The following table stratifies COB’s borrowings as short-term and long-term at the periods indicated:December 31,(dollars in thousands)20152014BalanceRateBalanceRateShort-term borrowings:Retail customer repurchase agreements$7,2190.21%$9,0760.21%Federal Home Loan Bank advances28,5000.49%——%Total short-term borrowings$35,719$9,076Long-term debt:Federal Home Loan Bank advances$65,1811.79$68,2341.68Long-term notes payable5,4151.435,3381.43Junior subordinated debt56,7021.9256,7021.78Total long-term debt$127,298$130,274                                                                             
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|(dollars in thousands)                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
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|Short-term borrowings:                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Retail customer repurchase agreements                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Federal Home Loan Bank advances                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Total short-term borrowings                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Long-term debt:                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Federal Home Loan Bank advances                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Long-term notes payable                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Junior subordinated debt                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Total long-term debt                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Schedule of Retail Repurchase Agreements and Federal Funds Purchased | Information concerning retail repurchase agreements and federal funds purchased is as follows:(dollars in thousands)201520142013RetailRepurchaseAgreementsRetailRepurchaseAgreementsRetailRepurchaseAgreementsBalance at December 31$7,219$9,076$6,917Average balance during the year10,0337,7139,852Maximum month end balance16,75312,21713,064Weighted average interest rate:At December 310.21%0.21%0.21%During the year0.220.210.21                                                                                                                                                                              
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|(dollars in thousands)                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
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|Balance at December 31                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Average balance during the year                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Maximum month end balance                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Weighted average interest rate:                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|At December 31                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|During the year                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|FHLB advance [Member]                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|**Debt Instrument [Line Items]**                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Scheduled Maturities of Long-term Debt                               | AtDecember 31, 2015, 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 31,2016$33,50020175,00020185,1812019—202050,0002021 and thereafter—Total FHLB advances$93,681                                                                                                                                                                                                                             
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|(dollars in thousands)                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Twelve Months Ended December 31,                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|2016                                                                 | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|2017                                                                 | 5,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|2018                                                                 | 5,181                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|2019                                                                 | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|2020                                                                 | 50,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|2021 and thereafter                                                  | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Total FHLB advances                                                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Schedule of Long-term Debt                                           | Long-term debt included the following advances from the FHLB at the periods indicated.(dollars in thousands)December 31,MaturityInterest Rate20152014September 8, 20153.7100%—3,000September 27, 20160.93005,0005,000September 27, 20171.42005,0005,000August 27, 20186.1500181234September 27, 20181.84005,0005,000June 15, 20201.893850,00050,000$65,181$68,234                                                                                                                                                                                                                                                    
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|(dollars in thousands)                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
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|Maturity                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|September 8, 2015                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|September 27, 2016                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|September 27, 2017                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|August 27, 2018                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|September 27, 2018                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|June 15, 2020                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
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|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)CommencementStatedof EarlyAs of December 31,MaturityRedemption20152014IssuerDatePeriodPrincipalUnpaid InterestPrincipalUnpaid InterestInterest RateFNB Trust I12/15/203512/15/2010$20,619$18$20,619$1,1073 month LIBOR + 1.37% =1.88% at 12/31/15FNB Trust II6/30/20366/30/201130,928—30,9281,5883 month LIBOR + 1.32% =1.65% at 12/31/15Catawba Trust II12/30/203212/30/20075,155—5,1556083 month LIBOR + 3.35% =3.68% at 12/31/15Total Junior Subordinated Debentures$56,702$18$56,702$3,303
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|(dollars in thousands)                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
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|Issuer                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|FNB Trust I                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|FNB Trust II                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Catawba Trust II                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Total Junior Subordinated Debentures                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

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