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Summary of Significant Accounting Policies (Details) | 9 Months Ended
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Sep. 30, 2020
Accounting Policies [Abstract] |
Percentage of Loan Portfolio Concentrated in Loans Secured by Real Estate | 75.00%

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- Definition Percentage of loan portfolio concentrated in loans secured by real estate. + References No definition available. + Details
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Namespace Prefix: | cban_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration