Fair Value Measurements (Unobservable Inputs In Level 3 Valuations Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (Weighted Average [Member], Significant Unobservable Inputs (Level 3) [Member], Fair Value, Measurements, Recurring [Member])	3 Months Ended	6 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Assets [Member] | Inventories Component [Member]
Unobservable inputs in Level 3 Valuations of Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Basis	26.90%	13.50%
Transportation cost	24.50%	8.40%
Assets [Member] | Commodity Derivative Contracts [Member]
Unobservable inputs in Level 3 Valuations of Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Basis	18.60%	45.70%
Transportation cost	10.50%	16.20%
Liabilities [Member] | Inventories Component [Member]
Unobservable inputs in Level 3 Valuations of Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Basis	4.90%	26.20%
Transportation cost	10.60%	9.10%
Liabilities [Member] | Commodity Derivative Contracts [Member]
Unobservable inputs in Level 3 Valuations of Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]
Basis	33.00%	17.00%
Transportation cost	15.30%	7.70%