| **Loans and Allowance for Loan Losses (Past Due Status) (Details) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2014                                                                                                                                                                                                                                                                                           | Dec. 31, 2013                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | $ 4,536us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue                                                                                                                                                                                                                                   | $ 6,588us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue                                                                                                                                                                                                                                   |
| 60 - 89 days past due                                                                                               | 647us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue                                                                                                                                                                                                                                       | 1,318us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue                                                                                                                                                                                                                                     |
| More than 90 days past due                                                                                          | 21,157us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue                                                                                                                                                                                                                      | 25,133us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue                                                                                                                                                                                                                      |
| Nonaccrual                                                                                                          | 25,288us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus                                                                                                                                                                                                                                     | 35,165us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus                                                                                                                                                                                                                                     |
| Total past due and nonaccrual                                                                                       | 51,628cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus                                                                                                                                                                                                                               | 68,204cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus                                                                                                                                                                                                                               |
| Current and accruing                                                                                                | 1,306,160cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing                                                                                                                                                                                                                                    | 1,144,044cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing                                                                                                                                                                                                                                    |
| Loans held for investment                                                                                           | 1,357,788us-gaap_LoansAndLeasesReceivableGrossCarryingAmount                                                                                                                                                                                                                                            | 1,212,248us-gaap_LoansAndLeasesReceivableGrossCarryingAmount                                                                                                                                                                                                                                            |
| Commercial and agricultural [Member]                                                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| Loans held for investment                                                                                           | 113,413us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                                                                                          | 72,252us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                                                                                           |
| Real estate - construction [Member]                                                                                 |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| Loans held for investment                                                                                           | 78,327us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                                                                                              | 64,083us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                                                                                              |
| Real estate - mortgage, 1-4 family residential [Member]                                                             |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| Loans held for investment                                                                                           | 667,602us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                                                                                                    | 636,107us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                                                                                                    |
| Real estate - mortgage, commercial [Member]                                                                         |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| Loans held for investment                                                                                           | 426,328us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                                                                                           | 394,924us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                                                                                           |
| Consumer [Member]                                                                                                   |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| Loans held for investment                                                                                           | 72,118us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                        | 44,882us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                        |
| PC [Member]                                                                                                         |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 3,668us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                               | 5,461us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                               |
| 60 - 89 days past due                                                                                               | 513us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                                 | 1,293us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                               |
| More than 90 days past due                                                                                          | 5us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                     | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                     |
| Nonaccrual                                                                                                          | 25,288us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                               | 35,165us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                               |
| Total past due and nonaccrual                                                                                       | 29,474cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                         | 41,919cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                         |
| Current and accruing                                                                                                | 1,205,472cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                              | 1,008,677cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                              |
| Loans held for investment                                                                                           | 1,234,946us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                                      | 1,050,596us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                                                                                                                                      |
| PC [Member] | Commercial and agricultural [Member]                                                                  |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 0us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember               | 18us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember              |
| 60 - 89 days past due                                                                                               | 0us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember               | 43us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember              |
| More than 90 days past due                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember |
| Nonaccrual                                                                                                          | 608us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember              | 516us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember              |
| Total past due and nonaccrual                                                                                       | 608cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember        | 577cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember        |
| Current and accruing                                                                                                | 105,269cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember            | 60,946cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember             |
| Loans held for investment                                                                                           | 105,877us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                    | 61,523us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                     |
| PC [Member] | Real estate - construction [Member]                                                                   |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 100us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                | 168us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                |
| 60 - 89 days past due                                                                                               | 0us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                  | 634us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                |
| More than 90 days past due                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember    | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember    |
| Nonaccrual                                                                                                          | 2,307us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember               | 4,677us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember               |
| Total past due and nonaccrual                                                                                       | 2,407cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember         | 5,479cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember         |
| Current and accruing                                                                                                | 66,723cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                | 48,711cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                |
| Loans held for investment                                                                                           | 69,130us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                        | 54,190us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                        |
| PC [Member] | Real estate - mortgage, 1-4 family residential [Member]                                               |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 2,719us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                     | 3,454us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                     |
| 60 - 89 days past due                                                                                               | 147us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                       | 522us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                       |
| More than 90 days past due                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember           | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember           |
| Nonaccrual                                                                                                          | 8,637us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                      | 11,580us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                     |
| Total past due and nonaccrual                                                                                       | 11,503cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember               | 15,556cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember               |
| Current and accruing                                                                                                | 638,364cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                      | 593,698cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                      |
| Loans held for investment                                                                                           | 649,867us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                              | 609,254us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                              |
| PC [Member] | Real estate - mortgage, commercial [Member]                                                           |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 105us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember              | 1,765us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember            |
| 60 - 89 days past due                                                                                               | 141us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember              | 77us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember               |
| More than 90 days past due                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember  | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember  |
| Nonaccrual                                                                                                          | 13,381us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember            | 18,380us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember            |
| Total past due and nonaccrual                                                                                       | 13,627cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember      | 20,222cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember      |
| Current and accruing                                                                                                | 325,356cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember             | 261,524cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember             |
| Loans held for investment                                                                                           | 338,983us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                     | 281,746us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                     |
| PC [Member] | Consumer [Member]                                                                                     |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 744us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                          | 56us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                           |
| 60 - 89 days past due                                                                                               | 225us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                          | 17us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                           |
| More than 90 days past due                                                                                          | 5us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember              | 0us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember              |
| Nonaccrual                                                                                                          | 355us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                           | 12us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                            |
| Total past due and nonaccrual                                                                                       | 1,329cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                   | 85cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                      |
| Current and accruing                                                                                                | 69,760cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                          | 43,798cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                          |
| Loans held for investment                                                                                           | 71,089us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                  | 43,883us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedContractsAndOriginatedLoansMember                                  |
| PI [Member]                                                                                                         |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 868us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                               | 1,127us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                             |
| 60 - 89 days past due                                                                                               | 134us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                               | 25us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                                |
| More than 90 days past due                                                                                          | 21,152us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                              | 25,133us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                              |
| Nonaccrual                                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                                  | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                                  |
| Total past due and nonaccrual                                                                                       | 22,154cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                       | 26,285cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                       |
| Current and accruing                                                                                                | 100,688cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                              | 135,367cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                              |
| Loans held for investment                                                                                           | 122,842us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                                      | 161,652us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                                                                                                                                      |
| PI [Member] | Commercial and agricultural [Member]                                                                  |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 0us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                             | 35us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            |
| 60 - 89 days past due                                                                                               | 0us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                             | 16us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            |
| More than 90 days past due                                                                                          | 2,232us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember           | 1,977us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember           |
| Nonaccrual                                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                              | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                              |
| Total past due and nonaccrual                                                                                       | 2,232cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                    | 2,028cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                    |
| Current and accruing                                                                                                | 5,303cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            | 8,701cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            |
| Loans held for investment                                                                                           | 7,535us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                    | 10,729us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                   |
| PI [Member] | Real estate - construction [Member]                                                                   |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 0us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                | 48us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                               |
| 60 - 89 days past due                                                                                               | 0us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                | 0us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                |
| More than 90 days past due                                                                                          | 3,737us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember              | 2,758us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember              |
| Nonaccrual                                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                 | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                 |
| Total past due and nonaccrual                                                                                       | 3,737cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                       | 2,806cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                       |
| Current and accruing                                                                                                | 5,460cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                               | 7,087cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                               |
| Loans held for investment                                                                                           | 9,197us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                       | 9,893us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                       |
| PI [Member] | Real estate - mortgage, 1-4 family residential [Member]                                               |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 579us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                     | 135us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                     |
| 60 - 89 days past due                                                                                               | 15us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                      | 9us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                       |
| More than 90 days past due                                                                                          | 2,209us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                     | 2,907us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                     |
| Nonaccrual                                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                        | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                        |
| Total past due and nonaccrual                                                                                       | 2,803cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                              | 3,051cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                              |
| Current and accruing                                                                                                | 14,934cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                     | 23,802cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                     |
| Loans held for investment                                                                                           | 17,737us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                             | 26,853us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                             |
| PI [Member] | Real estate - mortgage, commercial [Member]                                                           |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 287us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            | 903us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            |
| 60 - 89 days past due                                                                                               | 119us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            | 0us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                              |
| More than 90 days past due                                                                                          | 12,964us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember           | 17,479us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember           |
| Nonaccrual                                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                               | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                               |
| Total past due and nonaccrual                                                                                       | 13,370cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                    | 18,382cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                    |
| Current and accruing                                                                                                | 73,975cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            | 94,796cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                            |
| Loans held for investment                                                                                           | 87,345us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                    | 113,178us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                   |
| PI [Member] | Consumer [Member]                                                                                     |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                                |                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                    |
| 30 - 59 days past due                                                                                               | 2us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                          | 6us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                          |
| 60 - 89 days past due                                                                                               | 0us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                          | 0us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                          |
| More than 90 days past due                                                                                          | 10us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                           | 12us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                           |
| Nonaccrual                                                                                                          | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                           | 0us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                           |
| Total past due and nonaccrual                                                                                       | 12cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                    | 18cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                    |
| Current and accruing                                                                                                | 1,016cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                         | 981cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                           |
| Loans held for investment                                                                                           | $ 1,028us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                               | $ 999us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= cob_PurchasedImpairedLoansMember                                                 |

| X                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing Receivable, Recorded Investment, Current and Accruing
+ References
No definition available.
+ Details**Name:**cob_FinancingReceivableRecordedInvestmentCurrentAndAccruing**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing Receivable, Recorded Investment, Past Due and Nonaccrual Status
+ References
No definition available.
+ Details**Name:**cob_FinancingReceivableRecordedInvestmentPastDueAndNonaccrualStatus**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivables that are less than 60 days past due but more than 29 days past due.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953401-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivables that are less than 90 days past due but more than 59 days past due.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953401-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivables that are equal to or greater than 90 days past due.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953401-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5111-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522
+ Details**Name:**us-gaap_LoansAndLeasesReceivableGrossCarryingAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cob_CommercialAndAgriculturalPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cob_RealEstateConstructionPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=cob_PurchasedContractsAndOriginatedLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=cob_PurchasedImpairedLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |