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Fair Value of Financial Instruments and Fair Value Measurements - Narrative (Details) | Mar. 31, 2021
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Fair Value Disclosures [Abstract] |
Fair value input, discount amount | 10.00%

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- Definition Refers to the discounted rate to account for selling and marketing costs in fair value measurements. + References No definition available. + Details
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Namespace Prefix: | cban_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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