| **Loans and Allowance for Loan Losses (Details) (USD $)In Thousands, unless otherwise specified**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 3 Months Ended |     |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|-----|
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| **Financing Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |           |     |   |  |   |
| Allowance for Loan and Lease Losses, Write-offs                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | $ 1,977        |     | $ 3,010 |  |   |
| Allowance for Loan Losses, Recovery                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 1,915          |     | 3,227 |  |   |
| Allowance for Loan and Lease Losses, Net Write-downs                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | $ 62           |     | $ (217) |  |   |
| Loans and Leases Receivable, Ratio, Allowance for Loan and Lease Losses to Loans and Leases Receivables                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 2.13%          | [1] | 2.66% | [1] | 2.21% |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| [1]For Three Months Ended(dollars in thousands) March 31, 2014 March 31, 2013Balance, beginning of period $26,785 $29,314Provision for (recovery of) losses charged to continuing operations (684) 110Net recoveries (charge-offs): Charge-offs (1,977) (3,010)Recoveries 1,915 3,227Net recoveries (charge-offs) (62) 217Balance, end of period $26,039 $29,641Annualized net charge-offs (recoveries) during the period to average loans 0.02% (0.08)%Annualized net charge-offs (recoveries) during the period to ALL 0.97% (2.93)%Allowance for loan losses to loans held for investment 2.13% 2.66 % |

| X                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of net direct write-downs (net of recoveries) of financing receivables charged against the allowance.
+ References
No definition available.
+ Details**Name:**cob_AllowanceForLoanAndLeaseLossesNetWriteDowns**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of recovery of loans and leases receivable doubtful of collection that were previously charged off.
+ References
No definition available.
+ Details**Name:**cob_AllowanceForLoanLossesRecovery**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Allowance for loan and lease losses to loans and leases receivables ratio.
+ References
No definition available.
+ Details**Name:**cob_LoansAndLeasesReceivableRatioAllowanceForLoanAndLeaseLossesToLoansAndLeasesReceivables**Namespace Prefix:**cob_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5212-111524Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph d -Article 9
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