| **Short-Term Borrowings and Long-Term Debt (Junior Subordinated Debentures) (Details) (USD $)In Thousands, unless otherwise specified** | 12 Months Ended                                                                                                                                                                                                                                                                      |                                                                   |                                                                                                                                                                                                        |
|-----------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Debt Instrument [Line Items]**                                                                                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| Number of Junior Subordinated Debentures issued from funds invested from the sale of trust preferred securities                         | 2cob_JuniorSubordinatedDebenturesNumberIssuedResultingFromFundsInvestedfromtheSaleofTrustPreferredSecurities                                                                                                                                                                         |                                                              |                                                                                                                                                                                                   |
| Number of Junior Subordinated Debentures acquired from merger                                                                           |                                                                                                                                                                                                                                                                                 | 2cob_JuniorSubordinatedDebenturesNumberofIssuesAcquiredfromMerger |                                                                                                                                                                                                   |
| Junior Subordinated Debentures [Member]                                                                                                 |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| **Debt Instrument [Line Items]**                                                                                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| Principal                                                                                                                               | 56,702us-gaap_DebtInstrumentFaceAmount/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                                                                                                           |                                                              | $ 56,702us-gaap_DebtInstrumentFaceAmount/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                           |
| Interest Payable                                                                                                                        | 3,303us-gaap_InterestPayableCurrentAndNoncurrent/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                                                                                                 |                                                              | 2,235us-gaap_InterestPayableCurrentAndNoncurrent/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                   |
| Junior Subordinated Debentures [Member] | Issuer - FNB Trust I [Member]                                                                 |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| **Debt Instrument [Line Items]**                                                                                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| Principal                                                                                                                               | 20,619us-gaap_DebtInstrumentFaceAmount/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                              |                                                              | 20,619us-gaap_DebtInstrumentFaceAmount/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                |
| Interest Payable                                                                                                                        | 1,107us-gaap_InterestPayableCurrentAndNoncurrent/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                    |                                                              | 753us-gaap_InterestPayableCurrentAndNoncurrent/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember        |
| Junior Subordinated Debentures [Member] | Issuer - FNB Trust I [Member] | 3 month LIBOR [Member]                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| **Debt Instrument [Line Items]**                                                                                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| Variable rate basis                                                                                                                     | 3 month LIBOR                                                                                                                                                                                                                                                                        |                                                              |                                                                                                                                                                                                   |
| Basis spread on variable rate                                                                                                           | 1.37%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember      |                                                              |                                                                                                                                                                                                   |
| Interest rate at period end                                                                                                             | 1.61%us-gaap_DebtInstrumentInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember         |                                                              |                                                                                                                                                                                                   |
| Junior Subordinated Debentures [Member] | Issuer - FNB Trust II [Member]                                                                |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| **Debt Instrument [Line Items]**                                                                                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| Principal                                                                                                                               | 30,928us-gaap_DebtInstrumentFaceAmount/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                             |                                                              | 30,928us-gaap_DebtInstrumentFaceAmount/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember               |
| Interest Payable                                                                                                                        | 1,588us-gaap_InterestPayableCurrentAndNoncurrent/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                   |                                                              | 1,078us-gaap_InterestPayableCurrentAndNoncurrent/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember     |
| Junior Subordinated Debentures [Member] | Issuer - FNB Trust II [Member] | 3 month LIBOR [Member]                                       |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| **Debt Instrument [Line Items]**                                                                                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| Variable rate basis                                                                                                                     | 3 month LIBOR                                                                                                                                                                                                                                                                        |                                                              |                                                                                                                                                                                                   |
| Basis spread on variable rate                                                                                                           | 1.32%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember     |                                                              |                                                                                                                                                                                                   |
| Interest rate at period end                                                                                                             | 1.58%us-gaap_DebtInstrumentInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesFnbTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember        |                                                              |                                                                                                                                                                                                   |
| Junior Subordinated Debentures [Member] | Issuer - Catawba Trust II [Member]                                                            |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| **Debt Instrument [Line Items]**                                                                                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| Principal                                                                                                                               | 5,155us-gaap_DebtInstrumentFaceAmount/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesCatawbaTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                          |                                                              | 5,155us-gaap_DebtInstrumentFaceAmount/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesCatawbaTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember            |
| Interest Payable                                                                                                                        | 608us-gaap_InterestPayableCurrentAndNoncurrent/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesCatawbaTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember                                                                                 |                                                              | $ 404us-gaap_InterestPayableCurrentAndNoncurrent/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesCatawbaTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember |
| Junior Subordinated Debentures [Member] | Issuer - Catawba Trust II [Member] | 3 month LIBOR [Member]                                   |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| **Debt Instrument [Line Items]**                                                                                                        |                                                                                                                                                                                                                                                                                 |                                                              |                                                                                                                                                                                                   |
| Variable rate basis                                                                                                                     | 3 month LIBOR                                                                                                                                                                                                                                                                        |                                                              |                                                                                                                                                                                                   |
| Basis spread on variable rate                                                                                                           | 3.35%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesCatawbaTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember |                                                              |                                                                                                                                                                                                   |
| Interest rate at period end                                                                                                             | 3.61%us-gaap_DebtInstrumentInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_JuniorSubordinatedDebenturesCatawbaTrustIiMember/ us-gaap_LongtermDebtTypeAxis= us-gaap_JuniorSubordinatedDebtMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember    |                                                              |                                                                                                                                                                                                   |

| X                                                                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Junior Subordinated Debentures, Number Issued Resulting From Funds Invested from the Sale of Trust Preferred Securities
+ References
No definition available.
+ Details**Name:**cob_JuniorSubordinatedDebenturesNumberIssuedResultingFromFundsInvestedfromtheSaleofTrustPreferredSecurities**Namespace Prefix:**cob_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Junior Subordinated Debentures, Number of Issues Acquired from Merger
+ References
No definition available.
+ Details**Name:**cob_JuniorSubordinatedDebenturesNumberofIssuesAcquiredfromMerger**Namespace Prefix:**cob_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage points added to the reference rate to compute the variable rate on the debt instrument.
+ References
No definition available.
+ Details**Name:**us-gaap_DebtInstrumentBasisSpreadOnVariableRate1**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.
+ References
No definition available.
+ Details**Name:**us-gaap_DebtInstrumentDescriptionOfVariableRateBasis**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Face (par) amount of debt instrument at time of issuance.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400
+ Details**Name:**us-gaap_DebtInstrumentFaceAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The effective interest rate at the end of the reporting period.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
+ Details**Name:**us-gaap_DebtInstrumentInterestRateAtPeriodEnd**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of interest payable on debt, including, but not limited to, trade payables.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.15(5)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.15(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Subparagraph a -Article 7Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Subparagraph 5 -Article 9
+ Details**Name:**us-gaap_InterestPayableCurrentAndNoncurrent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LongtermDebtTypeAxis=us-gaap_JuniorSubordinatedDebtMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |