Note 4 - Allowance for Loan Losses (Details) - Allowance for Loan Losses - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Commercial and Agricultural
Allowance for loan losses, beginning balance			$ 8,802	$ 11,806
Allowance for loan losses, charge-offs			(1,776)	(3,933)
Allowance for loan losses, recoveries			635	607
Allowance for loan losses, provision	$ 250	$ 500	741	1,308
Allowance for loan losses, ending balance	8,402	9,788	8,402	9,788
Allowance for loan losses, individually evaluated for impairment	713	1,077	713	1,077
Allowance for loan losses, collectively evaluated for impairment	7,689	8,711	7,689	8,711
Loans receivable, individually evaluated for impairment	27,917	31,018	27,917	31,018
Loans receivable, collectively evaluated for impairment	736,287	712,263	736,287	712,263
Loans receivable	764,204	743,281	764,204	743,281	$ 746,094
Commercial and Agricultural Portfolio Segment [Member] \| Commercial [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			497	1,017
Allowance for loan losses, charge-offs			(257)	(453)
Allowance for loan losses, recoveries			45	69
Allowance for loan losses, provision			17	29
Allowance for loan losses, ending balance	302	662	302	662
Allowance for loan losses, individually evaluated for impairment	91	99	91	99
Allowance for loan losses, collectively evaluated for impairment	211	563	211	563
Loans receivable, individually evaluated for impairment	91	100	91	100
Loans receivable, collectively evaluated for impairment	48,668	46,381	48,668	46,381
Loans receivable	48,759	46,481	48,759	46,481	50,960
Commercial and Agricultural Portfolio Segment [Member] \| Agricultural [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			304	294
Allowance for loan losses, charge-offs			(5)	0
Allowance for loan losses, recoveries			3	2
Allowance for loan losses, provision			4	8
Allowance for loan losses, ending balance	306	304	306	304
Allowance for loan losses, individually evaluated for impairment	0	0	0	0
Allowance for loan losses, collectively evaluated for impairment	306	304	306	304
Loans receivable, individually evaluated for impairment	8	0	8	0
Loans receivable, collectively evaluated for impairment	27,365	23,017	27,365	23,017
Loans receivable	27,373	23,017	27,373	23,017	16,689
Real Estate Portfolio Segment [Member] \| Commercial [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			3,665	4,379
Allowance for loan losses, charge-offs			(275)	(761)
Allowance for loan losses, recoveries			138	109
Allowance for loan losses, provision			296	522
Allowance for loan losses, ending balance	3,824	4,249	3,824	4,249
Allowance for loan losses, individually evaluated for impairment	243	283	243	283
Allowance for loan losses, collectively evaluated for impairment	3,581	3,966	3,581	3,966
Loans receivable, individually evaluated for impairment	20,049	21,348	20,049	21,348
Loans receivable, collectively evaluated for impairment	327,654	306,150	327,654	306,150
Loans receivable	347,703	327,498	347,703	327,498	332,231
Real Estate Portfolio Segment [Member] \| Commercial Constuction [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			1,223	1,782
Allowance for loan losses, charge-offs			(96)	(1,541)
Allowance for loan losses, recoveries			282	302
Allowance for loan losses, provision			282	499
Allowance for loan losses, ending balance	1,691	1,042	1,691	1,042
Allowance for loan losses, individually evaluated for impairment	14	59	14	59
Allowance for loan losses, collectively evaluated for impairment	1,677	983	1,677	983
Loans receivable, individually evaluated for impairment	2,694	3,039	2,694	3,039
Loans receivable, collectively evaluated for impairment	40,895	47,416	40,895	47,416
Loans receivable	43,589	50,455	43,589	50,455	51,259
Real Estate Portfolio Segment [Member] \| Residential Construction [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			138	138
Allowance for loan losses, charge-offs			0	0
Allowance for loan losses, recoveries			0	0
Allowance for loan losses, provision			0	0
Allowance for loan losses, ending balance	138	138	138	138
Allowance for loan losses, individually evaluated for impairment	0	0	0	0
Allowance for loan losses, collectively evaluated for impairment	138	138	138	138
Loans receivable, individually evaluated for impairment	0	0	0	0
Loans receivable, collectively evaluated for impairment	10,465	9,700	10,465	9,700
Loans receivable	10,465	9,700	10,465	9,700	11,221
Real Estate Portfolio Segment [Member] \| Residential [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			2,425	3,278
Allowance for loan losses, charge-offs			(910)	(670)
Allowance for loan losses, recoveries			95	27
Allowance for loan losses, provision			85	150
Allowance for loan losses, ending balance	1,695	2,785	1,695	2,785
Allowance for loan losses, individually evaluated for impairment	308	605	308	605
Allowance for loan losses, collectively evaluated for impairment	1,387	2,180	1,387	2,180
Loans receivable, individually evaluated for impairment	3,380	5,522	3,380	5,522
Loans receivable, collectively evaluated for impairment	192,420	198,791	192,420	198,791
Loans receivable	195,800	204,313	195,800	204,313	203,753
Real Estate Portfolio Segment [Member] \| Farmland [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			104	312
Allowance for loan losses, charge-offs			(40)	(234)
Allowance for loan losses, recoveries			10	20
Allowance for loan losses, provision			3	6
Allowance for loan losses, ending balance	77	104	77	104
Allowance for loan losses, individually evaluated for impairment	57	31	57	31
Allowance for loan losses, collectively evaluated for impairment	20	73	20	73
Loans receivable, individually evaluated for impairment	1,695	1,009	1,695	1,009
Loans receivable, collectively evaluated for impairment	59,856	49,392	59,856	49,392
Loans receivable	61,551	50,401	61,551	50,401	49,951
Consumer and Other Portfolio Segment [Member] \| Consumer [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			67	243
Allowance for loan losses, charge-offs			(167)	(274)
Allowance for loan losses, recoveries			47	64
Allowance for loan losses, provision			53	93
Allowance for loan losses, ending balance	0	126	0	126
Allowance for loan losses, individually evaluated for impairment	0	0	0	0
Allowance for loan losses, collectively evaluated for impairment	0	126	0	126
Loans receivable, individually evaluated for impairment	0	0	0	0
Loans receivable, collectively evaluated for impairment	20,958	23,448	20,958	23,448
Loans receivable	20,958	23,448	20,958	23,448	22,820
Consumer and Other Portfolio Segment [Member] \| Other [Member]
Commercial and Agricultural
Allowance for loan losses, beginning balance			379	363
Allowance for loan losses, charge-offs			(26)	0
Allowance for loan losses, recoveries			15	14
Allowance for loan losses, provision			1	1
Allowance for loan losses, ending balance	369	378	369	378
Allowance for loan losses, individually evaluated for impairment	0	0	0	0
Allowance for loan losses, collectively evaluated for impairment	369	378	369	378
Loans receivable, individually evaluated for impairment	0	0	0	0
Loans receivable, collectively evaluated for impairment	8,006	7,968	8,006	7,968
Loans receivable	$ 8,006	$ 7,968	$ 8,006	$ 7,968	$ 7,210

No definition available.

Name:	cban_CommercialAndAgriculturalAbstract00000
Namespace Prefix:	cban_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for 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 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1

+ Details

Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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=28367877&loc=d3e4428-111522

+ Details

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

- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.11)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

+ Details

Name:	us-gaap_ProvisionForLoanAndLeaseLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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_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_CommercialConstuctionMember
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cban_OtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: