Note 3 - Age Analysis of Past Due Loans and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Commercial and Agricultural Portfolio Segment [Member] \| Commercial [Member] \| Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	$ 320	$ 491
Commercial and Agricultural Portfolio Segment [Member] \| Commercial [Member]
Accruing loans past due	320	491
Nonaccrual loans	461	577
Current loans	47,153	46,714
Loans and Leases Receivable, Gross	47,934	47,782	$ 52,506
Commercial and Agricultural Portfolio Segment [Member] \| Agricultural [Member] \| Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	104	71
Commercial and Agricultural Portfolio Segment [Member] \| Agricultural [Member]
Accruing loans past due	104	71
Nonaccrual loans	192	178
Current loans	24,011	18,944
Loans and Leases Receivable, Gross	24,307	19,193	24,019
Real Estate Portfolio Segment [Member] \| Commercial [Member] \| Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	1,452	6,031
Real Estate Portfolio Segment [Member] \| Commercial [Member]
Accruing loans past due	1,452	6,031
Nonaccrual loans	7,678	7,565
Current loans	336,051	332,666
Loans and Leases Receivable, Gross	345,181	346,262	341,167
Real Estate Portfolio Segment [Member] \| Commercial Construction [Member] \| Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	148	90
Real Estate Portfolio Segment [Member] \| Commercial Construction [Member]
Accruing loans past due	148	90
Nonaccrual loans	190	1,643
Current loans	31,954	38,374
Loans and Leases Receivable, Gross	32,292	40,107	46,699
Real Estate Portfolio Segment [Member] \| Residential Construction [Member]
Current loans	9,141	9,413
Loans and Leases Receivable, Gross	9,141	9,413	11,327
Real Estate Portfolio Segment [Member] \| Residential [Member] \| Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	3,123	3,683
Real Estate Portfolio Segment [Member] \| Residential [Member]
Accruing loans past due	3,123	3,683
Nonaccrual loans	3,455	3,164
Current loans	189,562	190,155
Loans and Leases Receivable, Gross	196,140	197,002	202,805
Real Estate Portfolio Segment [Member] \| Farmland [Member] \| Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	220	123
Real Estate Portfolio Segment [Member] \| Farmland [Member]
Accruing loans past due	220	123
Nonaccrual loans	933	1,103
Current loans	68,984	60,554
Loans and Leases Receivable, Gross	70,137	61,780	54,135
Consumer and Other Portfolio Segment [Member] \| Consumer [Member] \| Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	244	470
Consumer and Other Portfolio Segment [Member] \| Consumer [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due		8
Consumer and Other Portfolio Segment [Member] \| Consumer [Member]
Accruing loans past due	244	478
Nonaccrual loans	240	178
Current loans	19,452	19,949
Loans and Leases Receivable, Gross	19,936	20,605	21,371
Consumer and Other Portfolio Segment [Member] \| Other [Member]
Current loans	19,141	16,492
Loans and Leases Receivable, Gross	19,141	16,492	6,049
Financing Receivables, 30-89 Days Past Due [Member]
Accruing loans past due	5,611	10,959
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accruing loans past due		8
Accruing loans past due	5,611	10,967
Nonaccrual loans	13,149	14,408
Current loans	745,449	733,261
Loans and Leases Receivable, Gross	$ 764,209	$ 758,636	$ 760,078

Financing receivables that are current.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953401-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5111-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953401-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=cban_CommercialAndAgriculturalPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_CommercialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=cban_FinancingReceivables3089DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_AgriculturalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=cban_RealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_CommercialConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_ResidentialConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_ResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_FarmlandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=cban_ConsumerAndOtherPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_ConsumerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_OtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: