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Summary of Significant Accounting Policies (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of Significant Accounting Policies
Realization of brokered natural gas margin	$ 5.5	$ 7.4	$ 8.8
Total sales
Credit Risk
Threshold percentage which the entity uses for disclosure		10.00%
Customer
Credit Risk
Number of customers	3
Customer one
Credit Risk
Percentage of total sales	18.00%		11.00%
Number of customers			1
Customer two
Credit Risk
Percentage of total sales	12.00%
Customer three
Credit Risk
Percentage of total sales	10.00%

X

- Definition

Margin related to brokering natural gas, a result of buying and selling natural gas in back-to-back transactions, during the reporting period.

+ References

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the number of customers.

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- Definition

Threshold percentage which the entity uses for disclosure.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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