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

No definition available.

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

No definition available.

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Area of land held.

No definition available.

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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
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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
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Cash payments to lessor's for use of assets under operating leases.

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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 946
-SubTopic 220
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-Section S99
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-Subparagraph (SX 210.6-07(2)(c)(2)(i))
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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Data Type:	xbrli:stringItemType
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Period Type:	duration

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Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=ccoi_AuditoriumSuitableForTrainingMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=ccoi_DataCenterInBuildingMember
Namespace Prefix:
Data Type:	na
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Namespace Prefix:
Data Type:	na
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Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	srt_CounterpartyNameAxis=ccoi_SodiumLlcMember
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Data Type:	na
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Name:	srt_CounterpartyNameAxis=ccoi_ThoriumLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
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