Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) (Commodity Contract [Member], USD $)	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Commodity Contract [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 41,660,000	$ 16,649,000
Purchases	1,056,000	0
Settlements	(53,809,000)	(12,449,000)
Gains (losses) recognized in earnings	999,000	(62,000)
Gains recognized as regulatory assets and liabilities	34,311,000	3,504,000
Balance at end of period	24,217,000	7,642,000
Transfers into Level 3	0	0
Transfers out of Level 3	$ 0	$ 0

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Amount of gain (loss) recognized in the income statement of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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Amount of purchases of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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

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Amount of settlements of financial instrument classified as a derivative asset (liability) after deduction of derivative liability, measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset) out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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This element represents total gains (losses) for the period (realized and unrealized), arising from net assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are recognized in regulatory assets and liabilities.

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No definition available.

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