Derivative Instruments and Hedging Activities Notional Contracts by Derivative Type (Details)	3 Months Ended
	Dec. 31, 2017 MMBTU bbl
Produced Gasoline Member | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	250,000
Natural Gas - long [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	7,200,000
NYMEX WTI Short [Member] | Economic Hedges [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	1,175,000
Forward Contracts [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	276,751
Forward Contracts [Member] | Economic Hedges [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	85,000
Maturing in Next Twelve Months [Member] | Produced Gasoline Member | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	250,000
Maturing in Next Twelve Months [Member] | Natural Gas - long [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	1,800,000
Maturing in Next Twelve Months [Member] | Forward Contracts [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	276,751
Maturing in Year Two [Member] | Natural Gas - long [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	1,800,000
Maturing in Year Four [Member] | Natural Gas - long [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	1,800,000