| **Fair Values of Assets and Liabilities (Measured on Nonrecurring Basis) (Details) (Nonrecurring [Member], USD $)In Thousands, unless otherwise specified** | Jun. 30, 2014 | Dec. 31, 2013 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Total [Member]                                                                                                                                              |          |          |
| **Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]**                                                                          |          |          |
| Impaired loans, net                                                                                                                                         | $ 8,837       | $ 2,038       |
| Other real estate owned                                                                                                                                     | 17,956        | 18,263        |
| Total assets at fair value                                                                                                                                  | 26,793        | 20,301        |
| Level 1 [Member]                                                                                                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]**                                                                          |          |          |
| Impaired loans, net                                                                                                                                         | 0             | 0             |
| Other real estate owned                                                                                                                                     | 0             | 0             |
| Total assets at fair value                                                                                                                                  | 0             | 0             |
| Level 2 [Member]                                                                                                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]**                                                                          |          |          |
| Impaired loans, net                                                                                                                                         | 0             | 0             |
| Other real estate owned                                                                                                                                     | 0             | 0             |
| Total assets at fair value                                                                                                                                  | 0             | 0             |
| Level 3 [Member]                                                                                                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]**                                                                          |          |          |
| Impaired loans, net                                                                                                                                         | 8,837         | 2,038         |
| Other real estate owned                                                                                                                                     | 17,956        | 18,263        |
| Total assets at fair value                                                                                                                                  | $ 26,793      | $ 20,301      |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.
+ References
No definition available.
+ Details**Name:**cob_ForeclosedAssetFairValueDisclosure**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.
+ References
No definition available.
+ Details**Name:**cob_ImpairedFinancingReceivableFairValueDisclosure**Namespace Prefix:**cob_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258
+ Details**Name:**us-gaap_AssetsFairValueDisclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |