Fair Value Measurements - Narratives (Details)	12 Months Ended
Dec. 31, 2018 USD ($) Impaired_Asset_And_Liabilty	Dec. 31, 2017 USD ($) Impaired_Asset_And_Liabilty	Dec. 31, 2016 USD ($) Impaired_Asset_And_Liabilty
Fair Value Disclosures [Abstract]
Fair value assets Level 1 to Level 2 transfers amount	$ 0	$ 0	$ 0
Fair value liabilities Level 1 to Level 2 transfers amount	0	0	0
Fair value assets Level 2 to Level 1 transfers amount	0	0	0
Fair value liabilities Level 2 to Level 1 transfers amount	$ 0	$ 0	$ 0
Number of non-financial assets and liabilities impaired \| Impaired_Asset_And_Liabilty	0	0	0

Represents the number of non-financial assets and liabilities that were impaired during the period.

No definition available.

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Namespace Prefix:	cog_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

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

- Definition

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of transfers of liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

+ Details

Name:	us-gaap_FairValueLiabilitiesLevel1ToLevel2TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of transfers of liabilities measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

+ Details

Name:	us-gaap_FairValueLiabilitiesLevel2ToLevel1TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant