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, 2017 USD ($)
Colony Bankcorp Statutory Trust III [Member]
Issuance date	Jun. 17, 2004
Debt amount	$ 4,640
Total interest rate	4.00111%
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	1.32111%
Added points	2.68%
Colony Bankcorp Capital Trust I [Member]
Issuance date	Apr. 13, 2006
Debt amount	$ 5,155
Total interest rate	2.835%
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	1.335%
Added points	1.50%
Colony Bankcorp Capital Trust II [Member]
Issuance date	Mar. 12, 2007
Debt amount	$ 9,279
Total interest rate	2.985%
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	1.335%
Added points	1.65%
Colony Bankcorp Capital Trust III [Member]
Issuance date	Sep. 14, 2007
Debt amount	$ 5,155
Total interest rate	2.71111%
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	1.31111%
Added points	1.40%

Minimum redemption date.

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- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	cban_
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- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

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Balance Type:	na
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- 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/presentationRef
-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

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- 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://www.xbrl.org/2003/role/presentationRef
-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

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- Details

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- Details

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