| **Short-Term Borrowings and Long-Term Debt (FHLB Advances) (Details) (USD $)**     | Dec. 31, 2014                                                                                                                                                                               | Dec. 31, 2013                                                                                                                                  | Jun. 30, 2013                                               |
|------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------|
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | $ 68,234,000us-gaap_FederalHomeLoanBankAdvancesLongTerm                                                                                                                                     | $ 73,283,000us-gaap_FederalHomeLoanBankAdvancesLongTerm                                                                                        |                                                        |
| FHLB Advances, interest rate, ranging from                                         | 0.93%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateRangeFrom                                                                                              | 0.93%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateRangeFrom                                                 |                                                        |
| FHLB Advances, interest rate, ranging to                                           | 6.15%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateRangeTo                                                                                                | 6.15%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateRangeTo                                                   |                                                        |
| **Scheduled Maturities of FHLB Advances**                                          |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| 2015                                                                               | 3,000,000us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate                                                                                             |                                                                                                                                           |                                                        |
| 2016                                                                               | 5,000,000us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneToTwoYearsOfBalanceSheetDate                                                                                         |                                                                                                                                           |                                                        |
| 2017                                                                               | 5,000,000us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromTwoToThreeYearsOfBalanceSheetDate                                                                                       |                                                                                                                                           |                                                        |
| 2018                                                                               | 5,234,000us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromThreeToFourYearsOfBalanceSheetDate                                                                                      |                                                                                                                                           |                                                        |
| 2019                                                                               | 0us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromFourToFiveYearsOfBalanceSheetDate                                                                                               |                                                                                                                                           |                                                        |
| 2020 and thereafter                                                                | 50,000,000us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueAfterFiveYearsOfBalanceSheetDate                                                                                           |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 68,234,000us-gaap_FederalHomeLoanBankAdvancesLongTerm                                                                                                                                       | 73,283,000us-gaap_FederalHomeLoanBankAdvancesLongTerm                                                                                          |                                                        |
| FHLB advances restructured                                                         |                                                                                                                                                                                        |                                                                                                                                           | 50,000,000cob_FederalHomeLoanBankAdvancesAmountRestructured |
| FHLB Advances, Maturing December 29, 2014 [Member]                                 |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 0us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingDecember292014Member                                                       | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingDecember292014Member  |                                                        |
| **Scheduled Maturities of FHLB Advances**                                          |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 0us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingDecember292014Member                                                       | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingDecember292014Member  |                                                        |
| FHLB Advances, interest rate                                                       | 3.3125%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingDecember292014Member |                                                                                                                                           |                                                        |
| FHLB Advances, Maturing September 8, 2015 [Member]                                 |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 3,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember82015Member                                               | 3,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember82015Member  |                                                        |
| **Scheduled Maturities of FHLB Advances**                                          |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 3,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember82015Member                                               | 3,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember82015Member  |                                                        |
| FHLB Advances, interest rate                                                       | 3.71%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember82015Member   |                                                                                                                                           |                                                        |
| FHLB Advances, Maturing September 27, 2016 [Member]                                |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272016Member                                              | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272016Member |                                                        |
| **Scheduled Maturities of FHLB Advances**                                          |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272016Member                                              | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272016Member |                                                        |
| FHLB Advances, interest rate                                                       | 0.93%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272016Member  |                                                                                                                                           |                                                        |
| FHLB Advances, Maturing September 27, 2017 [Member]                                |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272017Member                                              | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272017Member |                                                        |
| **Scheduled Maturities of FHLB Advances**                                          |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272017Member                                              | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272017Member |                                                        |
| FHLB Advances, interest rate                                                       | 1.42%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272017Member  |                                                                                                                                           |                                                        |
| FHLB Advances, Maturing August 27, 2018 [Member]                                   |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 234,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingAugust272018Member                                                   | 283,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingAugust272018Member      |                                                        |
| **Scheduled Maturities of FHLB Advances**                                          |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 234,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingAugust272018Member                                                   | 283,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingAugust272018Member      |                                                        |
| FHLB Advances, interest rate                                                       | 6.15%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingAugust272018Member     |                                                                                                                                           |                                                        |
| FHLB Advances, Maturing September 27, 2018 [Member]                                |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272018Member                                              | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272018Member |                                                        |
| **Scheduled Maturities of FHLB Advances**                                          |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272018Member                                              | 5,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272018Member |                                                        |
| FHLB Advances, interest rate                                                       | 1.84%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingSeptember272018Member  |                                                                                                                                           |                                                        |
| FHLB Advances, Maturing June 15, 2020 [Member]                                     |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 50,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingJune152020Member                                                  | 50,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingJune152020Member     |                                                        |
| **Scheduled Maturities of FHLB Advances**                                          |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB advances                                                                      | 50,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingJune152020Member                                                  | 50,000,000us-gaap_FederalHomeLoanBankAdvancesLongTerm/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingJune152020Member     |                                                        |
| FHLB Advances, interest rate                                                       | 1.6224%us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd/ us-gaap_DebtInstrumentAxis= cob_FederalHomeLoanBankAdvancesMaturingJune152020Member     |                                                                                                                                           |                                                        |
| CommunityOne [Member]                                                              |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| **Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]**             |                                                                                                                                                                                        |                                                                                                                                           |                                                        |
| FHLB Advances, available borrowing capacity without pledging additional collateral | 130,800,000cob_FederalHomeLoanBankAdvancesGeneralDebtObligationsAmountOfAvailableUnusedFundsNoAdditionalCollateralPledged/ dei_LegalEntityAxis= cob_CommunityoneMember                      |                                                                                                                                           |                                                        |
| FHLB Advances, additional borrowing by pledging additional collateral              | $ 202,500,000cob_FederalHomeLoanBankAdvancesGeneralDebtObligationsAmountOfAvailableUnusedFundsByPledgingAdditionalCollateral/ dei_LegalEntityAxis= cob_CommunityoneMember                   |                                                                                                                                           |                                                        |

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Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds, by Pledging Additional Collateral
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
States the interest rate applicable to Federal Home Loan Bank advances outstanding as of the Balance Sheet date.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
States the lowest interest rate applicable to any of the advances from the Federal Home Loan Bank as of the Balance Sheet date.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
States the highest interest rate applicable to any of the advances from the Federal Home Loan Bank as of the Balance Sheet date.
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| - Definition
Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.
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| - Definition
Amount of federal home loan bank advances maturing after the fifth fiscal year following the latest fiscal year.
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| - Definition
Amount of federal home loan bank advances maturing in the fifth fiscal year following the latest fiscal year.
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| - Definition
Amount of federal home loan bank advances maturing in the second fiscal year following the latest fiscal year.
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Amount of federal home loan bank advances maturing in the fourth fiscal year following the latest fiscal year.
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Amount of federal home loan bank advances maturing in the third fiscal year following the latest fiscal year.
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| - Definition
Amount of federal home loan bank advances maturing in the next fiscal year following the latest fiscal year.
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