Other Real Estate Owned and Property Acquired in Settlement of Loans (Changes in Real Estate Acquired in Settlement) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Real Estate Acquired Through Foreclosure [Roll Forward]
Real estate acquired in settlement of loans, beginning of period	$ 13,845	$ 20,833	$ 16,251	$ 20,122
Plus: New real estate acquired in settlement of loans	2,143	938	2,202	3,433
Plus: Real estate acquired in BOGC acquisition	0	0
Less: Sales of real estate acquired in settlement of loans	(1,794)	(1,663)	(3,758)	(3,153)
Less: Write-downs and net loss on sales charged to expense	(3)	(391)	(504)	(685)
Real estate acquired in settlement of loans, end of period	$ 14,191	$ 19,717	$ 14,191	$ 19,717

This amount represents new real estate acquired in settlement of loans (net of write downs) during the period.

No definition available.

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- Definition

Real Estate Acquired Through Foreclosure, Additions from Acquisitions

+ References

No definition available.

+ Details

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Definition

This amount represents write-downs on the existing real estate acquired through foreclosure and net gain (loss) on the sales of real estate acquired through foreclosure during the period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

This amount represents sale of real estate acquired in settlement of loans during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	cob_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5162-111524

Reference 2: 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 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 28
-Article 12

Reference 4: 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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Period Type:	instant