| **Other Real Estate Owned and Personal Property Acquired in Settlement of Loans (Tables)** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
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| **Repossessed Assets [Abstract]**                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Schedule of Repossessed Assets                                                             | The following table summarizes real estate acquired in settlement of loans and personal property acquired in settlement of loans at the periods indicated:(dollars in thousands) December 31, 2013 December 31, 2012Real estate acquired in settlement of loans $28,353 $62,796Personal property acquired in settlement of loans 42 335Total property acquired in settlement of loans $28,395 $63,131                                                                                                                                                                                                    |
| Activities of Real Estate Acquired through Foreclosure                                     | The following table summarize the changes in real estate acquired in settlement of loans at the periods indicated:  For Year Ended(dollars in thousands) December 31, 2013 December 31, 2012Real estate acquired in settlement of loans, beginning of period $62,796 $110,009Plus:  New real estate acquired in settlement of loans 15,001 32,565Less:  Sales of real estate acquired in settlement of loans (45,523) (57,991)Less:  Write-downs and net loss on sales charged to expense (3,921) (21,787)Real estate acquired in settlement of loans, end of period $28,353 $62,796 |

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| - Definition
Tabular disclosure of the change in real estate assets taken in settlement of troubled loans through surrender or foreclosure.
+ References
No definition available.
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| - Definition
Tabular disclosure of real estate and personal property taken in settlement of troubled loans through surrender or foreclosure.
+ References
No definition available.
+ Details**Name:**cob_ScheduleOfRepossessedAssetsTableTextBlock**Namespace Prefix:**cob_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
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| - Details**Name:**us-gaap_ForeclosedAssetsAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |