Note 9 - Subordinated Debentures (Trust Preferred Securities) (Details)	6 Months Ended
Jun. 30, 2015
Subordinated Borrowings [Abstract]
Number of Deferred Consecutive Quarterly Periods Without Default Or Penalty Maximum	20

Maximum number of deferred consecutive quarterly periods without default or penalty for deferment of interest payment.

No definition available.

Name:	cban_NumberOfDeferredConsecutiveQuarterlyPeriodsWithoutDefaultOrPenaltyMaximum
Namespace Prefix:	cban_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration