Name:	ccoi_LesseeLeasingArrangementsRequiredNoticePeriodForCancellationOfLease
Namespace Prefix:	ccoi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Amount of the fixed annual rent per year under lease agreement.

No definition available.

Name:	ccoi_OperatingLeaseFixedAnnualRent
Namespace Prefix:	ccoi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Area of land held.

No definition available.

Name:	us-gaap_AreaOfLand
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

Indicates line item in statement of income or comprehensive income that includes operating lease income.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479016/842-30-45-3

Name:	us-gaap_OperatingLeaseIncomeComprehensiveIncomeExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	duration

Amount of operating lease income from lease payments and variable lease payments paid and payable to lessor. Includes, but is not limited to, variable lease payments not included in measurement of lease receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 270
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482964/270-10-50-6A

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479016/842-30-45-3

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

Amount of operating lease income from lease payments paid and payable to lessor. Excludes variable lease payments not included in measurement of lease receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 270
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482964/270-10-50-6A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-5

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

Cash payments to lessor's for use of assets under operating leases.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 25
-Subparagraph (g)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-25

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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_RelatedPartyTransactionAxis=ccoi_SecondAmendmentToOfficeLeaseWithGermaniumLlcWhichAmendsLeaseForTechnicalSpaceUnderNetworkOperationsLeaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=ccoi_AuditoriumSuitableForTrainingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=ccoi_DataCenterInBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_RelatedPartyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RelatedPartyTransactionAxis=ccoi_OfficeLeaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_CounterpartyNameAxis=ccoi_SodiumLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_CounterpartyNameAxis=ccoi_ThoriumLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RelatedPartyTransactionAxis=ccoi_NetworkOperationsLeaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: