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

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

No definition available.

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