Loans and Allowance for Loan Losses (Allowance for Loan Losses) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	$ 26,785	$ 29,314	$ 39,360
Provision for loan losses	(5,371)us-gaap_ProvisionForLoanAndLeaseLosses	523us-gaap_ProvisionForLoanAndLeaseLosses	14,049us-gaap_ProvisionForLoanAndLeaseLosses
Charge-offs	(7,703)	(13,344)	(30,968)
Recoveries	6,634cob_AllowanceForLoanLossesRecovery	10,292cob_AllowanceForLoanLossesRecovery	6,873cob_AllowanceForLoanLossesRecovery
Net charge-offs	(1,069)	(3,052)	(24,095)
Balance, end of period	$ 20,345	$ 26,785	$ 29,314
Annualized net charge-offs during the period to average loans	0.08%	0.26%	2.13%
Annualized net charge-offs during the period to ALL	5.25%	11.39%	82.20%
Allowance for loan losses to loans held for investment	1.50%	2.21%	2.41%

Amount of net direct write-downs (net of recoveries) of financing receivables charged against the allowance.

No definition available.

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- Definition

Amount of recovery of loans and leases receivable doubtful of collection that were previously charged off.

+ References

No definition available.

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- Definition

Allowance for loan and lease losses to loans and leases receivables ratio.

+ References

No definition available.

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- Definition

Net write-downs to allowance for loan and lease losses ratio.

+ References

No definition available.

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- Definition

Net write-downs to average loans and leases receivable ratio.

+ References

No definition available.

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- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

-Paragraph 15

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-Publisher SEC

-Name Regulation S-X (SX)

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-Section 03

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

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-Number Topic 6

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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

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