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Note 10 - Commitments and Contingencies (Details Textual) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Sep. 30, 2016 | Dec. 31, 2015
Construction [Member] |  |
Other Commitment |  | $ 1.2
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

X
- Definition Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions. + References No definition available. + Details
Name: | us-gaap_OtherCommitment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_OtherCommitmentsAxis=cban_ConstructionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |