Represents the available line of credit with an accordion feature.

No definition available.

Name:	cog_AvailableLineOfCredit
Namespace Prefix:	cog_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the required annual coverage ratio of operating cash flow to interest expense under the terms of the agreement.

+ References

No definition available.

+ Details

Name:	cog_DebtInstrumentCovenantAnnualCoverageRatio
Namespace Prefix:	cog_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the required asset coverage ratio under the terms of the agreement.

+ References

No definition available.

+ Details

Name:	cog_DebtInstrumentCovenantAssetCoverageRatio
Namespace Prefix:	cog_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of trailing quarters used to calculate the annual coverage ratio.

+ References

No definition available.

+ Details

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

- Definition

Number of institutional investors that purchased debt in a private placement offering.

+ References

No definition available.

+ Details

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

- Definition

For an unclassified balance sheet, the amount as of the balance sheet date of capitalized costs associated with the issuance of the original credit facility (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the amended credit facility. Such amount is before the consideration of accumulated amortization.

+ References

No definition available.

+ Details

Name:	cog_DeferredFinanceCostsGrossOriginalCreditFacility
Namespace Prefix:	cog_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash outflow for the amount of a make-whole premium paid due to the repayment of long-term debt prior to the due date.

+ References

No definition available.

+ Details

Name:	cog_EarlyRepaymentOfDebtPremium
Namespace Prefix:	cog_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Increased maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility, if any one or more of the existing banks or new banks agree to provide such increased commitment amount.

+ References

No definition available.

+ Details

Name:	cog_LineOfCreditFacilityContingentIncreaseToMaximumBorrowingCapacity
Namespace Prefix:	cog_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the period over which the entity has to reduce its outstanding borrowings in the event that the adjusted credit line available is less than outstanding borrowings.

+ References

No definition available.

+ Details

Name:	cog_LineOfCreditFacilityPeriodToReduceOutstandingDebtInEqualMonthlyInstallmentsToTheAdjustedCreditLineAvailable
Namespace Prefix:	cog_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the maturity period of long-term debt.

+ References

No definition available.

+ Details

Name:	cog_LongTermDebtMaturityPeriod
Namespace Prefix:	cog_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of tranches in which long-term debt is issued.

+ References

No definition available.

+ Details

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

- Definition

For an unclassified balance sheet, the amount, as of the balance sheet date, of remaining capitalized costs associated with the amended credit facility (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the amended credit facility. Such amount is before the consideration of accumulated amortization.

+ References

No definition available.

+ Details

Name:	cog_RemainingDeferredFinanceCostsUnderAmendedCreditFacility
Namespace Prefix:	cog_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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

- Definition

Interest rate stated in the contractual debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

For an unclassified balance sheet, the amount as of the balance sheet date of capitalized costs associated with the issuance of debt instruments (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the debt instruments to which such costs pertain. Such amount is before the consideration of accumulated amortization.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28555-108399

+ Details

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

Debt and Credit Agreements (Details 2) (USD $)	1 Months Ended	12 Months Ended	1 Months Ended					12 Months Ended	1 Months Ended						1 Months Ended				12 Months Ended		12 Months Ended
Debt and Credit Agreements (Details 2) (USD $)	Jul. 31, 2001 7.33% Weighted-Average Fixed Rate Notes tranche investor	Dec. 31, 2012 7.33% Weighted-Average Fixed Rate Notes Greater than quarter	Dec. 31, 2010 7.33% Weighted-Average Fixed Rate Notes Tranche 1 due July 2011	Jul. 31, 2001 7.33% Weighted-Average Fixed Rate Notes Tranche 1 due July 2011	Jul. 31, 2001 7.33% Weighted-Average Fixed Rate Notes Tranche 2 due July 2013	Jul. 31, 2001 7.33% Weighted-Average Fixed Rate Notes Tranche 3 due July 2026	Jul. 31, 2008 6.51% Weighted-Average Fixed Rate Notes tranche investor	Dec. 31, 2012 6.51% Weighted-Average Fixed Rate Notes Greater than quarter	Jul. 31, 2008 6.51% Weighted-Average Fixed Rate Notes Tranche 1 due July 2018	Jul. 31, 2008 6.51% Weighted-Average Fixed Rate Notes Tranche 2 due July 2020	Jul. 31, 2008 6.51% Weighted-Average Fixed Rate Notes Tranche 3 due July 2023	Dec. 31, 2008 9.78% Notes investor	Dec. 31, 2012 9.78% Notes	Dec. 31, 2011 9.78% Notes	Dec. 31, 2010 5.58% Weighted-Average Fixed Rate Notes investor tranche	Dec. 31, 2010 5.58% Weighted-Average Fixed Rate Notes Tranche 1 due January 2021	Dec. 31, 2010 5.58% Weighted-Average Fixed Rate Notes Tranche 2 due January 2023	Dec. 31, 2010 5.58% Weighted-Average Fixed Rate Notes Tranche 3 due January 2026	Dec. 31, 2012 Revolving Credit Facility quarter	May 31, 2012 Revolving Credit Facility	Dec. 31, 2012 Revolving Credit Facility Greater than
Debt
Number of institutional investors that purchased debt in a private placement offering	7						41					4			8
Number of tranches	3						3								3
Principal	$ 170,000,000			$ 75,000,000	$ 75,000,000	$ 20,000,000	$ 425,000,000		$ 245,000,000	$ 100,000,000	$ 80,000,000	$ 67,000,000			$ 175,000,000	$ 88,000,000	$ 25,000,000	$ 62,000,000
Term				10 years	12 years	15 years			10 years	12 years	15 years	10 years				10 years	12 years	15 years
Coupon (as a percent)				7.26%	7.36%	7.46%			6.44%	6.54%	6.69%	9.78%	9.78%	9.78%		5.42%	5.59%	5.80%
Asset coverage ratio		1.75						1.75													1.75
Annual coverage ratio		2.8						2.8													2.8
Number of trailing quarters used to calculate annual coverage ratio		4						4											4
Payment of make-whole premium due to early repayment of debt			2,800,000
Maximum borrowing capacity																			1,700,000,000	900,000,000
Contingent increase of maximum borrowing capacity																				500,000,000
Capitalized debt issuance costs																			5,000,000	5,000,000
Unamortized debt issuance costs associated with the original credit facility																				1,300,000
Period to reduce outstanding debt in equal monthly installments to the adjusted credit line available																			6 months
Remaining unamortized costs under amended credit facility																				$ 11,000,000