Commitments and Contingencies (Details 1) (USD $)	1 Months Ended
Feb. 28, 2011	Jun. 30, 2011
Targa North Texas LP [Member]
Long Term Supply Commitment [Line Items]
Obligated to pay annual fees per ("Mcf") for 2011		$ 1.1
Obligated to pay annual fees per thousand cubic feet ("Mcf") for 2012		1.15
Obligated to pay annual fees per thousand cubic feet ("Mcf") for 2013		1.25
Amount paid under settlement of obligation	2,134,000
Amount under accrued obligation		907,000
Fort Union Gas Gathering [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Obligated to pay for gathering agreements for 2011		3,220,000
Obligated to pay for gathering agreements for 2012		7,154,000
Obligated to pay for gathering agreements for 2013		7,665,000
Obligated to pay for gathering agreements for 2014		7,665,000
Obligated to pay for gathering agreements for 2015		7,665,000
Obligated to pay for gathering agreements for thereafter		$ 14,700,000

Amount paid under settlement of obligation.

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- Definition

Amount under accrued obligation.

+ Details

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- Definition

Long Term Supply Commitment Line Items.

+ Details

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- Definition

Recorded Unconditional Purchase Obligation Due In Second Year in dollars Per Thousand Cubic .

+ Details

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Namespace Prefix:	cpno
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Recorded Unconditional Purchase Obligation Due Remainder Of Current Year in dollars per thousand cubic feet.

+ Details

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Namespace Prefix:	cpno
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Balance Type:	credit
Period Type:	instant

- Definition

Recorded Unconditional Purchase Obligation Due Within One Year In Dollars Per Thousand Cubic Feet.

+ Details

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- Definition

Unrecorded Unconditional Purchase Obligation Balance due Remainder Of Current Year.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Unrecorded Unconditional Purchase Obligation Balance due thereafter.

+ Details

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Namespace Prefix:	cpno
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Balance Type:	credit
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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation on the first anniversary of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 47
-Paragraph 7
-Subparagraph b

+ Details

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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation on the fourth anniversary of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 47
-Paragraph 7
-Subparagraph b

+ Details

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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation on the second anniversary of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 47
-Paragraph 7
-Subparagraph b

+ Details

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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation on the third anniversary of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 47
-Paragraph 7
-Subparagraph b

+ Details

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- Definition

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.

+ Details

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