Derivatives (Details Textuals) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Derivative [Line Items]
Maximum counterparty loss	$ 5.7
Maximum counterparty loss with netting feature	5.1
Cash Flow Liquid Swap [Member]
Derivative [Line Items]
Unrealized derivative fair value related to cash flow hedges to be reclassfied within 12 months	0.8
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0.9
Cash Flow Gas Swap [Member]
Derivative [Line Items]
Unrealized derivative fair value related to cash flow hedges to be reclassfied within 12 months	$ 0

The amount recognized in earnings related to the change in fair value during the period of derivative or nonderivative instruments designated as fair value hedging instruments.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 45

-Subparagraph a(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Definition

The estimated net amount of unrealized gains or losses on price risk cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 45

-Subparagraph b(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

The maximum potential exposure to credit losses on derivative contracts.

+ References

No definition available.

+ Details

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

- Definition

The net potential exposure to credit losses on derivative contracts

+ References

No definition available.

+ Details

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