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v3.21.2

Commitments and Contingencies - Narrative (Details) | 6 Months Ended
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Jun. 30, 2021
Commitments and Contingencies Disclosure [Abstract] |
Letter of credit, expiration date period | 1 year

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- Definition Refers to the expiration dates of letter of credit issued measured in years. + References No definition available. + Details
Name: | cban_ExpirationPeriodOfLetterOfCreditIssued
Namespace Prefix: | cban_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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