Fair Value (Details 3)	3 Months Ended
	Mar. 31, 2013
Unobservable inputs used in the valuation of Level 3 instruments of assets
Term of counterparty option to renew gas purchase agreement	5 years
Embedded Derivatives in commodity contracts | Assets | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of Assets
Forward ERCOT Pricing (per MegaWatt Hour)	31.33
Embedded Derivatives in commodity contracts | Assets | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of Assets
Forward ERCOT Pricing (per MegaWatt Hour)	72.19
Embedded Derivatives in commodity contracts | Liabilities | Significant unobservable inputs (Level 3)
Unobservable inputs used in the valuation of Level 3 instruments of assets
Probability of renewal (as a percent)	0.00%
Number of renewal periods	2
Term of counterparty option to renew gas purchase agreement	5 years
Embedded Derivatives in commodity contracts | Propane prices | Liabilities | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	0.92
Embedded Derivatives in commodity contracts | Propane prices | Liabilities | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	0.99
Embedded Derivatives in commodity contracts | Isobutane prices | Liabilities | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.39
Embedded Derivatives in commodity contracts | Isobutane prices | Liabilities | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.54
Embedded Derivatives in commodity contracts | Normal butane prices | Liabilities | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.28
Embedded Derivatives in commodity contracts | Normal butane prices | Liabilities | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.46
Embedded Derivatives in commodity contracts | Natural gasoline prices | Liabilities | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.71
Embedded Derivatives in commodity contracts | Natural gasoline prices | Liabilities | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	2.15
Embedded Derivatives in commodity contracts | Natural gas prices | Liabilities | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	4.04
Embedded Derivatives in commodity contracts | Natural gas prices | Liabilities | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	5.87