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

Refers to the expiration dates of letter of credit issued measured in years.

No definition available.

Name:	cban_ExpirationPeriodOfLetterOfCreditIssued
Namespace Prefix:	cban_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration