Other Real Estate Owned and Personal Property Acquired in Settlement of Loans (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Repossessed Assets [Abstract]
Decrease in total OREO and foreclosed assets	$ 8,000,000cob_IncreaseDecreaseInRepossessedAssets
Real estate acquired in settlement of loans	20,122,000	28,353,000	62,796,000
Personal property acquired in settlement of loans	289,000us-gaap_OtherForeclosedAssets	42,000us-gaap_OtherForeclosedAssets
Total property acquired in settlement of loans	$ 20,411,000us-gaap_ForeclosedAssets	$ 28,395,000us-gaap_ForeclosedAssets

The increase (decrease) during the reporting period in the value of repossessed assets.

No definition available.

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- Definition

Carrying amount as of the balance sheet date of 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

+ Details

Name:	us-gaap_ForeclosedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_ForeclosedAssetsAbstract
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Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of assets other than real property that were received in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance.

+ References

+ Details

Name:	us-gaap_OtherForeclosedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4437-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5

+ Details

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Balance Type:	debit
Period Type:	instant