Fair Value (Details 3) - Jun. 30, 2015 - Embedded derivatives in commodity contracts	item $ / MWh $ / MMBTU $ / item
Propane prices | Asset | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit)	0.44
Propane prices | Asset | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit)	0.61
Isobutane prices | Asset | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit)	0.59
Isobutane prices | Asset | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit)	0.82
Normal butane prices | Asset | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit)	0.58
Normal butane prices | Asset | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit)	0.79
Natural gasoline prices | Asset | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit)	1.22
Natural gasoline prices | Asset | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit)	1.34
Natural gas prices | Asset | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit) | $ / MMBTU	2.68
Natural gas prices | Asset | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward price (in dollars per unit) | $ / MMBTU	3.69
Embedded derivative in gas processing and purchase contract
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Number of renewal periods | item	2
Term of producer's option to renew gas purchase agreement	5 years
Embedded derivative in gas processing and purchase contract | Asset | Significant unobservable inputs (Level 3)
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Probability of renewal (as a percent)	0.00%
Embedded derivative in electricity purchase contract | Liability | Significant unobservable inputs (Level 3) | Minimum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward ERCOT Pricing (in dollars per unit) | $ / MWh	26.55
Embedded derivative in electricity purchase contract | Liability | Significant unobservable inputs (Level 3) | Maximum
Unobservable inputs used in the valuation of Level 3 instruments of Assets and Liabilities
Forward ERCOT Pricing (in dollars per unit) | $ / MWh	35.56