Note 9 - Subordinated Debentures (Trusted Preferred Securities) - Schedule of Subordinated Debentures (Details) - Trust Preferred Securities Subject to Mandatory Redemption [Member] $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Colony Bankcorp Statutory Trust III [Member]
Issuance date	Jun. 17, 2004
Debt amount	$ 4,640
Total interest rate	5.01415%
Maturity date	Jun. 14, 2034
5 year call option	Jun. 17, 2009
Colony Bankcorp Statutory Trust III [Member] \| London Interbank Offered Rate (LIBOR) [Member]
3 month LIBOR rate	2.33413%
Added points	0.0268%
Colony Bankcorp Capital Trust I [Member]
Issuance date	Apr. 13, 2006
Debt amount	$ 5,155
Total interest rate	3.896%
Maturity date	Apr. 13, 2036
5 year call option	Apr. 13, 2011
Colony Bankcorp Capital Trust I [Member] \| London Interbank Offered Rate (LIBOR) [Member]
3 month LIBOR rate	2.396%
Added points	0.015%
Colony Bankcorp Capital Trust II [Member]
Issuance date	Mar. 12, 2007
Debt amount	$ 9,279
Total interest rate	4.046%
Maturity date	Mar. 12, 2037
5 year call option	Mar. 12, 2012
Colony Bankcorp Capital Trust II [Member] \| London Interbank Offered Rate (LIBOR) [Member]
3 month LIBOR rate	2.396%
Added points	0.0165%
Colony Bankcorp Capital Trust III [Member]
Issuance date	Sep. 14, 2007
Debt amount	$ 5,155
Total interest rate	3.73888%
Maturity date	Sep. 14, 2037
5 year call option	Sep. 14, 2012
Colony Bankcorp Capital Trust III [Member] \| London Interbank Offered Rate (LIBOR) [Member]
3 month LIBOR rate	2.33888%
Added points	0.014%

Minimum redemption date.

No definition available.

Name:	cban_RedemptionDateMinimum
Namespace Prefix:	cban_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The rate which is used as a benchmark to determine the variable rates.

+ References

No definition available.

+ Details

Name:	cban_ReferenceRate
Namespace Prefix:	cban_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the debt instrument was issued, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentIssuanceDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebtPercentageBearingVariableInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_ScheduleOfSharesSubjectToMandatoryRedemptionBySettlementTermsAxis=us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=cban_ColonyBankcorpStatutoryTrustIIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=cban_ColonyBankcorpCapitalTrustIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=cban_ColonyBankcorpCapitalTrustIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=cban_ColonyBankcorpCapitalTrustIIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: