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, Recurring [Member]	Dec. 31, 2020	Dec. 31, 2019
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	4.30%	28.20%
Transportation cost	10.60%	24.70%
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	28.30%	16.00%
Transportation cost	1.90%	9.70%
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	13.70%	14.70%
Transportation cost	0.00%	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	0.70%	20.20%
Transportation cost	1.30%	3.10%