Fair Value (Details 3) (Embedded Derivatives in commodity contracts, Significant unobservable inputs (Level 3))	12 Months Ended
	Dec. 31, 2012 item
Assets | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of Assets
Forward ERCOT Pricing (per MegaWatt Hour)	28.79
Assets | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of Assets
Forward ERCOT Pricing (per MegaWatt Hour)	62.10
Liabilities
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
Propane prices | Liabilities | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	0.91
Propane prices | Liabilities | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.01
Isobutane prices | Liabilities | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.60
Isobutane prices | Liabilities | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.84
Normal butane prices | Liabilities | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.44
Normal butane prices | Liabilities | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.73
Natural gasoline prices | Liabilities | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	1.84
Natural gasoline prices | Liabilities | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	2.21
Natural gas prices | Liabilities | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	3.33
Natural gas prices | Liabilities | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of assets
Forward price (in dollars per unit)	6.22