| **Derivatives and Financial Instruments (Details) (USD $)**                                    | 12 Months Ended                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Number of interest rate derivatives                                                            | 2us-gaap_NumberOfInterestRateDerivativesHeld                                                                                                                                                                                                                                |                                                                                                                                                                                                                                             |   |   |
| Not designated as hedges [Member]                                                              |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Gain (loss) recognized                                                                         | $ 19,000us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember                                                                                                                                                              | $ (214,000)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember                                                                                                                                | $ 204,000us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember |   |
| Not designated as hedges [Member] | Interest Rate Lock Commitments [Member]                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Gain (loss) recognized                                                                         | 2,000us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember                                                                                | 4,000us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember                                                     | 152,000us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember |   |
| Not designated as hedges [Member] | Forward Contracts [Member]                                 |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Gain (loss) recognized                                                                         | 17,000us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_ForwardContractsMember/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember                                                                                          | (218,000)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_ForwardContractsMember/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember                                                            | 52,000us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_ForwardContractsMember/ us-gaap_HedgingDesignationAxis= us-gaap_NondesignatedMember |   |
| Designated as hedges [Member] | Interest rate swaps [Member]                                   |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Derivative notional amount                                                                     |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   | 40,000,000invest_DerivativeNotionalAmount/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateSwapMember/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember |
| Gain (loss), net of tax recognized in accumulated other comprehensive loss (effective portion) | (324,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateSwapMember/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember                    | 0us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateSwapMember/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember |   |   |
| Designated as hedges [Member] | Interest Rate Swap 1 [Member]                                  |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Derivative notional amount                                                                     |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   | 20,000,000invest_DerivativeNotionalAmount/ us-gaap_DerivativeInstrumentRiskAxis= cob_InterestRateSwap1Member/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember |
| Designated as hedges [Member] | Interest Rate Swap 1 [Member] | 3 month LIBOR [Member]         |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Basis spread on variable rate                                                                  | 140.00%us-gaap_DerivativeBasisSpreadOnVariableRate/ us-gaap_DerivativeInstrumentRiskAxis= cob_InterestRateSwap1Member/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember |                                                                                                                                                                                                                                             |   |   |
| Fixed interest rate                                                                            | 3.55%us-gaap_DerivativeFixedInterestRate/ us-gaap_DerivativeInstrumentRiskAxis= cob_InterestRateSwap1Member/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember           |                                                                                                                                                                                                                                             |   |   |
| Designated as hedges [Member] | Interest Rate Swap 2 [Member]                                  |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Derivative notional amount                                                                     |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   | $ 20,000,000invest_DerivativeNotionalAmount/ us-gaap_DerivativeInstrumentRiskAxis= cob_InterestRateSwap2Member/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember |
| Designated as hedges [Member] | Interest Rate Swap 2 [Member] | 3 month LIBOR [Member]         |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| **Derivative [Line Items]**                                                                    |                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                             |   |   |
| Basis spread on variable rate                                                                  | 138.00%us-gaap_DerivativeBasisSpreadOnVariableRate/ us-gaap_DerivativeInstrumentRiskAxis= cob_InterestRateSwap2Member/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember |                                                                                                                                                                                                                                             |   |   |
| Fixed interest rate                                                                            | 3.33%us-gaap_DerivativeFixedInterestRate/ us-gaap_DerivativeInstrumentRiskAxis= cob_InterestRateSwap2Member/ us-gaap_HedgingDesignationAxis= us-gaap_DesignatedAsHedgingInstrumentMember/ us-gaap_VariableRateAxis= us-gaap_LondonInterbankOfferedRateLIBORMember           |                                                                                                                                                                                                                                             |   |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B
+ Details**Name:**invest_DerivativeNotionalAmount**Namespace Prefix:**invest_**Data Type:**xbrli:monetaryItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The percentage points added to the reference rate to compute the variable rate on the interest rate derivative.
+ References
No definition available.
+ Details**Name:**us-gaap_DerivativeBasisSpreadOnVariableRate**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fixed interest rate related to the interest rate derivative.
+ References
No definition available.
+ Details**Name:**us-gaap_DerivativeFixedInterestRate**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959
+ Details**Name:**us-gaap_DerivativeGainLossOnDerivativeNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959
+ Details**Name:**us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of interest rate derivative instruments held by the entity at the reporting date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5580258-113959Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959
+ Details**Name:**us-gaap_NumberOfInterestRateDerivativesHeld**Namespace Prefix:**us-gaap_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |