| **Discontinued Operations (Tables)**                          | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
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| **Discontinued Operation, Additional Disclosures [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Schedule of Net Income (Loss) from Discontinued Operations    | Net loss from discontinued operations, net of tax, at the dates indicated were as follows:(dollars in thousands) Nine Months Ended September 30,  2013 2012Interest Income    Total interest income $— $—Interest Expense    Total interest expense — —Net Interest Income before Provision for Loan Losses — —Provision for loan losses — —Net Interest Income after Provision for Loan Losses — —Noninterest Income    Total noninterest income — —Noninterest Expense    Personnel expense — 1Net occupancy expense — 1Professional fees — 25Total noninterest expense — 27Loss before income taxes — (27)Income tax (benefit)/expense — —Net loss from discontinued operations, net of tax $— $(27) |

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| - Definition
Tabular disclosure of disposal groups, which may include the gain (loss) recognized in the income statement and the income statement caption that includes that gain (loss), amounts of revenues and pretax profit or loss reported in discontinued operations.
+ References
No definition available.
+ Details**Name:**cob_ScheduleOfDisposalGroupsIncludingDiscontinuedOperationsIncomeStatementDisclosureTableTextBlock**Namespace Prefix:**cob_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
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| - Details**Name:**us-gaap_DiscontinuedOperationAdditionalDisclosuresAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |