| **Loans and Allowance for Loan Losses (Evaluation for Impairment) (Details) (USD $)In Thousands, unless otherwise specified** | Mar. 31, 2015                                                                                                                                                                                                                    | Dec. 31, 2014                                                                                                                                                                                                                    | Mar. 31, 2014 | Dec. 31, 2013                                                                                                                                                                                |
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| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                            |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| ALL, individually evaluated for impairment                                                                                    | $ 364us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1                                                                                                                                      | $ 418us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1                                                                                                                                      |               |                                                                                                                                                                                         |   |
| ALL, collectively evaluated for impairment                                                                                    | 15,450us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment                                                                                                                                      | 16,690us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment                                                                                                                                      |               |                                                                                                                                                                                         |   |
| ALL, PI loans evaluated for credit impairment                                                                                 | 3,194us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality                                                                                                                                    | 3,237us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality                                                                                                                                    |               |                                                                                                                                                                                         |   |
| ALL, PI loans with no credit deterioration                                                                                    | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration                                                                                                                                                | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration                                                                                                                                                |               |                                                                                                                                                                                         |   |
| Total ALL evaluated for impairment                                                                                            | 19,008us-gaap_FinancingReceivableAllowanceForCreditLosses                                                                                                                                                                        | 20,345us-gaap_FinancingReceivableAllowanceForCreditLosses                                                                                                                                                                        |               | 26,039us-gaap_FinancingReceivableAllowanceForCreditLosses                                                                                                                                    | 26,785us-gaap_FinancingReceivableAllowanceForCreditLosses |
| Loans held for investment, individually evaluated for impairment                                                              | 29,689us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment                                                                                                                                                              | 34,482us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment                                                                                                                                                              |               |                                                                                                                                                                                         |   |
| Loans held for investment, collectively evaluated for impairment                                                              | 1,256,960us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment                                                                                                                                                           | 1,200,464us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment                                                                                                                                                           |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with subsequent credit deterioration                                                      | 105,662us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality                                                                                                                                                          | 118,701us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality                                                                                                                                                          |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with no credit deterioration                                                              | 3,600cob_FinancingReceivableAcquiredWithNoCreditDeterioration                                                                                                                                                                    | 4,141cob_FinancingReceivableAcquiredWithNoCreditDeterioration                                                                                                                                                                    |               |                                                                                                                                                                                         |   |
| Loans held for investment                                                                                                     | 1,395,911us-gaap_LoansAndLeasesReceivableGrossCarryingAmount                                                                                                                                                                     | 1,357,788us-gaap_LoansAndLeasesReceivableGrossCarryingAmount                                                                                                                                                                     | [1]           |                                                                                                                                                                                         |   |
| Commercial and agricultural [Member]                                                                                          |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                            |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| ALL, individually evaluated for impairment                                                                                    | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember      | 58us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember     |               |                                                                                                                                                                                         |   |
| ALL, collectively evaluated for impairment                                                                                    | 3,159us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember   | 3,600us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember   |               |                                                                                                                                                                                         |   |
| ALL, PI loans evaluated for credit impairment                                                                                 | 239us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember  | 257us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember  |               |                                                                                                                                                                                         |   |
| ALL, PI loans with no credit deterioration                                                                                    | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember            | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember            |               |                                                                                                                                                                                         |   |
| Total ALL evaluated for impairment                                                                                            | 3,398us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                     | 3,915us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                     |               | 3,441us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember | 2,931us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember |
| Loans held for investment, individually evaluated for impairment                                                              | 444us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                             | 498us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                             |               |                                                                                                                                                                                         |   |
| Loans held for investment, collectively evaluated for impairment                                                              | 108,348us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                         | 105,380us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                         |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with subsequent credit deterioration                                                      | 6,841us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                        | 7,535us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                        |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with no credit deterioration                                                              | 0cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                    | 0cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                    |               |                                                                                                                                                                                         |   |
| Loans held for investment                                                                                                     | 115,633us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                   | 113,413us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                   |               |                                                                                                                                                                                         |   |
| Real estate - construction [Member]                                                                                           |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                            |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| ALL, individually evaluated for impairment                                                                                    | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember         | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember         |               |                                                                                                                                                                                         |   |
| ALL, collectively evaluated for impairment                                                                                    | 2,337us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember      | 2,656us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember      |               |                                                                                                                                                                                         |   |
| ALL, PI loans evaluated for credit impairment                                                                                 | 783us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember     | 507us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember     |               |                                                                                                                                                                                         |   |
| ALL, PI loans with no credit deterioration                                                                                    | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember               | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember               |               |                                                                                                                                                                                         |   |
| Total ALL evaluated for impairment                                                                                            | 3,120us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                        | 3,163us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                        |               | 5,308us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember    | 5,233us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember |
| Loans held for investment, individually evaluated for impairment                                                              | 1,262us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                              | 2,344us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                              |               |                                                                                                                                                                                         |   |
| Loans held for investment, collectively evaluated for impairment                                                              | 72,808us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                             | 66,786us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                             |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with subsequent credit deterioration                                                      | 8,112us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                           | 8,619us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                           |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with no credit deterioration                                                              | 543cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                     | 578cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                     |               |                                                                                                                                                                                         |   |
| Loans held for investment                                                                                                     | 82,725us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                       | 78,327us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                       |               |                                                                                                                                                                                         |   |
| Real estate - mortgage, 1-4 family residential [Member]                                                                       |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                            |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| ALL, individually evaluated for impairment                                                                                    | 353us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember              | 331us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember              |               |                                                                                                                                                                                         |   |
| ALL, collectively evaluated for impairment                                                                                    | 5,030us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember             | 5,317us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember             |               |                                                                                                                                                                                         |   |
| ALL, PI loans evaluated for credit impairment                                                                                 | 240us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember            | 199us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember            |               |                                                                                                                                                                                         |   |
| ALL, PI loans with no credit deterioration                                                                                    | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                      | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                      |               |                                                                                                                                                                                         |   |
| Total ALL evaluated for impairment                                                                                            | 5,623us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                               | 5,847us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                               |               | 7,923us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember           | 8,869us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember |
| Loans held for investment, individually evaluated for impairment                                                              | 11,596us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                    | 11,409us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                    |               |                                                                                                                                                                                         |   |
| Loans held for investment, collectively evaluated for impairment                                                              | 648,184us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                   | 638,456us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                   |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with subsequent credit deterioration                                                      | 13,272us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                 | 14,174us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                 |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with no credit deterioration                                                              | 3,057cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                          | 3,563cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                          |               |                                                                                                                                                                                         |   |
| Loans held for investment                                                                                                     | 676,109us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                             | 667,602us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                             |               |                                                                                                                                                                                         |   |
| Real estate - mortgage, commercial [Member]                                                                                   |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                            |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| ALL, individually evaluated for impairment                                                                                    | 11us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember      | 29us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember      |               |                                                                                                                                                                                         |   |
| ALL, collectively evaluated for impairment                                                                                    | 1,397us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember    | 2,065us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember    |               |                                                                                                                                                                                         |   |
| ALL, PI loans evaluated for credit impairment                                                                                 | 1,744us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember | 2,085us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember |               |                                                                                                                                                                                         |   |
| ALL, PI loans with no credit deterioration                                                                                    | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember             | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember             |               |                                                                                                                                                                                         |   |
| Total ALL evaluated for impairment                                                                                            | 3,152us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                      | 4,179us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                      |               | 6,966us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember  | 7,195us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember |
| Loans held for investment, individually evaluated for impairment                                                              | 16,387us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                           | 20,231us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                           |               |                                                                                                                                                                                         |   |
| Loans held for investment, collectively evaluated for impairment                                                              | 345,229us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                          | 318,752us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                          |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with subsequent credit deterioration                                                      | 76,489us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                        | 87,345us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                        |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with no credit deterioration                                                              | 0cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                     | 0cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                     |               |                                                                                                                                                                                         |   |
| Loans held for investment                                                                                                     | 438,105us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                    | 426,328us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                    |               |                                                                                                                                                                                         |   |
| Consumer [Member]                                                                                                             |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                            |                                                                                                                                                                                                                             |                                                                                                                                                                                                                             |               |                                                                                                                                                                                         |   |
| ALL, individually evaluated for impairment                                                                                    | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                   | 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                   |               |                                                                                                                                                                                         |   |
| ALL, collectively evaluated for impairment                                                                                    | 3,527us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                | 3,052us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                |               |                                                                                                                                                                                         |   |
| ALL, PI loans evaluated for credit impairment                                                                                 | 188us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember               | 189us-gaap_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember               |               |                                                                                                                                                                                         |   |
| ALL, PI loans with no credit deterioration                                                                                    | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                         | 0cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                         |               |                                                                                                                                                                                         |   |
| Total ALL evaluated for impairment                                                                                            | 3,715us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                  | 3,241us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                  |               | 2,401us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember              | 2,557us-gaap_FinancingReceivableAllowanceForCreditLosses/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember |
| Loans held for investment, individually evaluated for impairment                                                              | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                            | 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                            |               |                                                                                                                                                                                         |   |
| Loans held for investment, collectively evaluated for impairment                                                              | 82,391us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                       | 71,090us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                       |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with subsequent credit deterioration                                                      | 948us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                       | 1,028us-gaap_FinancingReceivableAcquiredWithDeterioratedCreditQuality/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                     |               |                                                                                                                                                                                         |   |
| Loans held for investment, PI loans with no credit deterioration                                                              | 0cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                 | 0cob_FinancingReceivableAcquiredWithNoCreditDeterioration/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                 |               |                                                                                                                                                                                         |   |
| Loans held for investment                                                                                                     | $ 83,339us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                               | $ 72,118us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                               |               |                                                                                                                                                                                         |   |
|                                                                                                                               |
| [1]Derived from audited consolidated financial statements                                                                     |

| X                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The balance of financing receivables that were acquired with no credit deterioration.
+ References
No definition available.
+ Details**Name:**cob_FinancingReceivableAcquiredWithNoCreditDeterioration**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The valuation allowance for financing recievable acquired with no credit deterioration.
+ References
No definition available.
+ Details**Name:**cob_FinancingReceivableAllowanceForCreditLossesAcquiredWithNoCreditDeterioration**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The balance of financing receivables that were acquired with deteriorated credit quality.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A valuation allowance for financing receivables that are expected to be uncollectible.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524
+ Details**Name:**us-gaap_FinancingReceivableAllowanceForCreditLosses**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The valuation allowance for financing receivables acquired with deteriorated credit quality.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524
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| X                                                                                                                                                                                        |
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| - Details**Name:**us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The balance of financing receivables that were collectively evaluated for impairment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The balance of financing receivables that were individually evaluated for impairment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953423-111524
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| 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
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| X                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| 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:** |