| **Other Real Estate Owned and Property Acquired in Settlement of Loans (Tables)** | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
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| **Repossessed Assets [Abstract]**                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Schedule of Repossessed Assets                                                    | The following table summarizes OREO and property acquired in settlement of loans at the periods indicated:(dollars in thousands) March 31, 2015 December 31, 2014Real estate acquired in settlement of loans $20,833 $20,122Property acquired in settlement of loans 207 289Total property acquired in settlement of loans $21,040 $20,411                                                                                                                                                                                                                                                                                                     |
| Activities of Real Estate Acquired through Foreclosure                            | The following tables summarize the changes in real estate acquired in settlement of loans at the periods indicated:  For Three Months Ended(dollars in thousands) March 31, 2015 March 31, 2014Real estate acquired in settlement of loans, beginning of period $20,122 $28,353Plus:  New real estate acquired in settlement of loans 2,495 268Less:  Sales of real estate acquired in settlement of loans (1,490) (3,774)Less:  Write-downs and net gain (loss) on sales charged to expense (294) (274)Real estate acquired in settlement of loans, end of period $20,833 $24,573      |

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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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| X                                                                                                                                                                                                                                                                                                                                                            |
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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 |