| **Income Taxes (Narrative) (Details) (USD $)**                                                                         | 12 Months Ended                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| Net deferred tax assets                                                                                                | $ 146,433,000us-gaap_DeferredTaxAssetsLiabilitiesNet                                                                                                                                                 | $ 10,215,000us-gaap_DeferredTaxAssetsLiabilitiesNet |   |
| Valuation allowance                                                                                                    | 1,300,000us-gaap_DeferredTaxAssetsValuationAllowance                                                                                                                                                 | 148,043,000us-gaap_DeferredTaxAssetsValuationAllowance |   |
| Amount in retained earnings for additions to the tax bad debt reserve for which no federal tax provision has been made | 5,000,000cob_DeferredTaxLiabilityAdditionsToTaxBadDebtReserveNoFederalTaxProvisionMade                                                                                                               |   |   |
| Deferred tax assets related to NOL carryforwards                                                                       | 137,412,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwards                                                                                                                                       | 135,050,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwards |   |
| Increase (decrease) in valuation allowance                                                                             | 146,743,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount                                                                                                                                  | 34,578,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount | (15,392,000)us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount |
| Granite Corp. [Member]                                                                                                 |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| Deferred tax assets related to NOL carryforwards                                                                       |                                                                                                                                                                                                 | 2,900,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwards/ us-gaap_BusinessAcquisitionAxis= cob_GraniteCorpMember |   |
| Increase (decrease) in valuation allowance                                                                             |                                                                                                                                                                                                 | (28,300,000)us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount/ us-gaap_BusinessAcquisitionAxis= cob_GraniteCorpMember |   |
| Federal Tax Authority [Member]                                                                                         |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| Operating loss carryforwards                                                                                           | 355,900,000us-gaap_OperatingLossCarryforwards/ us-gaap_IncomeTaxAuthorityAxis= us-gaap_DomesticCountryMember                                                                                         | 349,600,000us-gaap_OperatingLossCarryforwards/ us-gaap_IncomeTaxAuthorityAxis= us-gaap_DomesticCountryMember |   |
| Federal Tax Authority [Member] | Minimum [Member]                                                                      |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| Remaining carryforward periods                                                                                         | 15 years                                                                                                                                                                                             |   |   |
| Federal Tax Authority [Member] | Maximum [Member]                                                                      |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| Remaining carryforward periods                                                                                         | 19 years                                                                                                                                                                                             |   |   |
| State Jurisdiction [Member]                                                                                            |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| Operating loss carryforwards                                                                                           | 371,800,000us-gaap_OperatingLossCarryforwards/ us-gaap_IncomeTaxAuthorityAxis= us-gaap_StateAndLocalJurisdictionMember                                                                               | 365,800,000us-gaap_OperatingLossCarryforwards/ us-gaap_IncomeTaxAuthorityAxis= us-gaap_StateAndLocalJurisdictionMember |   |
| Increase (decrease) in valuation allowance                                                                             | $ (5,300,000)us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount/ us-gaap_IncomeTaxAuthorityAxis= us-gaap_StateAndLocalJurisdictionMember                                                       |   |   |
| State income tax rate                                                                                                  | 6.90%cob_EffectiveIncomeTaxRateReconciliationatStateStatutoryIncomeTaxRatePercent/ us-gaap_IncomeTaxAuthorityAxis= us-gaap_StateAndLocalJurisdictionMember                                           |   |   |
| State Jurisdiction [Member] | Minimum [Member]                                                                         |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| Remaining carryforward periods                                                                                         | 10 years                                                                                                                                                                                             |   |   |
| State Jurisdiction [Member] | Maximum [Member]                                                                         |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| Remaining carryforward periods                                                                                         | 14 years                                                                                                                                                                                             |   |   |
| Tax Year 2014 [Member] | State Jurisdiction [Member]                                                                   |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| State income tax rate                                                                                                  | 6.00%cob_EffectiveIncomeTaxRateReconciliationatStateStatutoryIncomeTaxRatePercent/ us-gaap_IncomeTaxAuthorityAxis= us-gaap_StateAndLocalJurisdictionMember/ cob_TaxPeriodAxis= cob_TaxYear2014Member |   |   |
| Tax Year 2015 [Member] | State Jurisdiction [Member]                                                                   |                                                                                                                                                                                                 |   |   |
| **Income Tax [Line Items]**                                                                                            |                                                                                                                                                                                                 |   |   |
| State income tax rate                                                                                                  | 5.00%cob_EffectiveIncomeTaxRateReconciliationatStateStatutoryIncomeTaxRatePercent/ us-gaap_IncomeTaxAuthorityAxis= us-gaap_StateAndLocalJurisdictionMember/ cob_TaxPeriodAxis= cob_TaxYear2015Member |   |   |

| X                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Deferred Tax Liability, Additions to Tax Bad Debt Reserve, No Federal Tax Provision Made
+ References
No definition available.
+ Details**Name:**cob_DeferredTaxLiabilityAdditionsToTaxBadDebtReserveNoFederalTaxProvisionMade**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Effective Income Tax Rate Reconciliation, at State Statutory Income Tax Rate, Percent
+ References
No definition available.
+ Details**Name:**cob_EffectiveIncomeTaxRateReconciliationatStateStatutoryIncomeTaxRatePercent**Namespace Prefix:**cob_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cob_IncomeTaxLineItems**Namespace Prefix:**cob_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Operating Loss Carryforwards, Remaining Carryforward Period
+ References
No definition available.
+ Details**Name:**cob_OperatingLossCarryforwardsRemainingCarryforwardPeriod**Namespace Prefix:**cob_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32537-109319
+ Details**Name:**us-gaap_DeferredTaxAssetsLiabilitiesNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 20 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28680-109314
+ Details**Name:**us-gaap_DeferredTaxAssetsOperatingLossCarryforwards**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32537-109319
+ Details**Name:**us-gaap_DeferredTaxAssetsValuationAllowance**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319
+ Details**Name:**us-gaap_OperatingLossCarryforwards**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of the change in the period in the valuation allowance for a specified deferred tax asset.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=21917399&loc=d3e32123-109318
+ Details**Name:**us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cob_TaxPeriodAxis=cob_TaxYear2014Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cob_TaxPeriodAxis=cob_TaxYear2015Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_BusinessAcquisitionAxis=cob_GraniteCorpMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_IncomeTaxAuthorityAxis=us-gaap_DomesticCountryMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_IncomeTaxAuthorityAxis=us-gaap_StateAndLocalJurisdictionMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |