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]	Dec. 31, 2018	Dec. 31, 2017
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	18.50%	12.80%
Transportation cost	25.90%	19.20%
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	21.60%	24.20%
Transportation cost	29.50%	12.50%
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	125.00%	99.90%
Transportation cost	39.40%	0.00%
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	19.10%	23.00%
Transportation cost	35.10%	10.40%