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Fair Value Measurements - Narrative (Additional Information) (Details) - impaired_asset_and_liability | 9 Months Ended
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Sep. 30, 2015 | Sep. 30, 2014
Fair Value Disclosures [Abstract] |  |
Number of non-financial assets and liabilities impaired | 0 | 0

X
- Definition Represents the number of non-financial assets and liabilities that were impaired during the period. + References No definition available. + Details
Name: | cog_NumberOfNonFinancialAssetsAndLiabilitiesImpaired
Namespace Prefix: | cog_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration