| **Loans and Allowance for Loan Losses (Credit Quality Indicator) (Details) (USD $)** | Dec. 31, 2014                                                                                                                                                                                                                                                        | Dec. 31, 2013                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | $ 1,357,788,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount                                                                                                                                                                                                   | $ 1,212,248,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount                                                                                                                                                                                                   |
| Loans and Leases Receivable, Deferred Income                                         | (3,200,000)us-gaap_LoansAndLeasesReceivableDeferredIncome                                                                                                                                                                                                            | 3,600,000us-gaap_LoansAndLeasesReceivableDeferredIncome                                                                                                                                                                                                              |
| Servicing Assets, Unconsolidated Loans Serviced, Unpaid Principal Balance            | 235,000,000cob_ServicingAssetsUnconsolidatedLoansServicedUnpaidPrincipalBalance                                                                                                                                                                                      | 190,200,000cob_ServicingAssetsUnconsolidatedLoansServicedUnpaidPrincipalBalance                                                                                                                                                                                      |
| Commercial and agricultural [Member]                                                 |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 113,413,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                                                   | 72,252,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember                                                                    |
| Real estate - construction [Member]                                                  |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 78,327,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                                                       | 64,083,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember                                                                       |
| Real estate - mortgage, 1-4 family residential [Member]                              |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 667,602,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                                                             | 636,107,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember                                                                             |
| Real estate - mortgage, commercial [Member]                                          |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 426,328,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                                                    | 394,924,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember                                                                    |
| Consumer [Member]                                                                    |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 72,118,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                 | 44,882,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                 |
| Substandard or Doubtful [Member]                                                     |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans purchased in the Merger                                                        | 27,000,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet/ us-gaap_InternalCreditAssessmentAxis= cob_SubstandardOrDoubtfulMember                                                                                              | 40,500,000us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet/ us-gaap_InternalCreditAssessmentAxis= cob_SubstandardOrDoubtfulMember                                                                                              |
| Pass [Member]                                                                        |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 1,254,674,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember                                                                                                                                           | 1,070,830,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember                                                                                                                                           |
| Pass [Member] | Commercial and agricultural [Member]                                 |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 104,165,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember         | 67,277,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember          |
| Pass [Member] | Real estate - construction [Member]                                  |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 68,995,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember             | 50,138,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember             |
| Pass [Member] | Real estate - mortgage, 1-4 family residential [Member]              |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 646,897,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember                   | 601,304,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember                   |
| Pass [Member] | Real estate - mortgage, commercial [Member]                          |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 363,267,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember          | 307,661,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember          |
| Pass [Member] | Consumer [Member]                                                    |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 71,350,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember                       | 44,450,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_PassMember                       |
| Special Mention [Member]                                                             |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 39,818,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember                                                                                                                                    | 45,884,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember                                                                                                                                    |
| Special Mention [Member] | Commercial and agricultural [Member]                      |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 6,318,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember | 1,262,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember |
| Special Mention [Member] | Real estate - construction [Member]                       |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 2,411,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember    | 3,984,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember    |
| Special Mention [Member] | Real estate - mortgage, 1-4 family residential [Member]   |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 5,363,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember           | 10,887,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember          |
| Special Mention [Member] | Real estate - mortgage, commercial [Member]               |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 25,715,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember | 29,711,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember |
| Special Mention [Member] | Consumer [Member]                                         |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 11,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember                 | 40,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SpecialMentionMember                 |
| Substandard [Member]                                                                 |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 62,553,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember                                                                                                                                       | 95,189,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember                                                                                                                                       |
| Substandard [Member] | Commercial and agricultural [Member]                          |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 2,930,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember    | 3,713,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember    |
| Substandard [Member] | Real estate - construction [Member]                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 6,921,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember       | 9,961,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember       |
| Substandard [Member] | Real estate - mortgage, 1-4 family residential [Member]       |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 15,342,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember             | 23,916,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember             |
| Substandard [Member] | Real estate - mortgage, commercial [Member]                   |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 36,984,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember    | 57,552,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember    |
| Substandard [Member] | Consumer [Member]                                             |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 376,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember                   | 47,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_SubstandardMember                    |
| Doubtful [Member]                                                                    |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 743,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                                                                                                                                             | 345,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                                                                                                                                             |
| Doubtful [Member] | Commercial and agricultural [Member]                             |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember               | 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_CommercialAndAgriculturalPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember               |
| Doubtful [Member] | Real estate - construction [Member]                              |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                  | 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= cob_RealEstateConstructionPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                  |
| Doubtful [Member] | Real estate - mortgage, 1-4 family residential [Member]          |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                         | 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ResidentialPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                         |
| Doubtful [Member] | Real estate - mortgage, commercial [Member]                      |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | 362,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember          | 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialRealEstatePortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                |
| Doubtful [Member] | Consumer [Member]                                                |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| **Financing Receivable, Recorded Investment [Line Items]**                           |                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                 |
| Loans held for investment                                                            | $ 381,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                    | $ 345,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember/ us-gaap_InternalCreditAssessmentAxis= us-gaap_DoubtfulMember                    |

| X                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This represents the unpaid principal balance of the unconsolidated loans serviced under the servicing contract.
+ References
No definition available.
+ Details**Name:**cob_ServicingAssetsUnconsolidatedLoansServicedUnpaidPrincipalBalance**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses).  This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 15 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544
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| - Definition
Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.
+ References
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| - 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
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