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Note 15 - Commitments and Contingencies (Details Textual) | 12 Months Ended
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Dec. 31, 2017
Expiration Period Of Letter Of Credit Issued | 1 year

X
- 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