Derivative Instruments And Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative Asset Fair Value Net Asset	$ 4,421	$ 17,588
Derivative Liability Fair Value Net Liability	3,781	14,215
Accrued Liabilities [Member]
Derivative [Line Items]
Derivative Liability Fair Value Net Liability	3,723	12,985
Prepayments And Other [Member]
Derivative [Line Items]
Derivative Asset Fair Value Net Asset	4,421	17,588
Other Noncurrent Liabilities [Member]
Derivative [Line Items]
Derivative Liability Fair Value Net Liability	58	1,230
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	915	7,526
Derivative Asset Fair Value Gross Liability	(263)	(1,784)
Derivative Asset Fair Value Net Asset	652	5,742
Derivative Liability Fair Value Gross Liability	58	1,230
Derivative Liability Fair Value Net Liability	58	1,230
Derivative Liability, Fair Value, Gross Asset	0	0
Designated as Hedging Instrument [Member] \| Commodity price swaps
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	915	7,526
Derivative Asset Fair Value Gross Liability	(263)	(1,784)
Derivative Asset Fair Value Net Asset	652	5,742
Derivative Liability Fair Value Gross Liability	58	1,230
Derivative Liability Fair Value Net Liability	58	1,230
Derivative Liability, Fair Value, Gross Asset	0	0
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	3,769	11,846
Derivative Asset Fair Value Gross Liability	0	0
Derivative Asset Fair Value Net Asset	3,769	11,846
Derivative Liability Fair Value Gross Liability	5,531	12,985
Derivative Liability Fair Value Net Liability	3,723	12,985
Derivative Liability, Fair Value, Gross Asset	(1,808)	0
Not Designated as Hedging Instrument [Member] \| Commodity forward contracts
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	71
Derivative Asset Fair Value Gross Liability	0
Derivative Asset Fair Value Net Asset	71
Derivative Liability Fair Value Gross Liability	58
Derivative Liability Fair Value Net Liability	58
Derivative Liability, Fair Value, Gross Asset	0
Not Designated as Hedging Instrument [Member] \| NYMEX futures contracts
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,530	0
Derivative Asset Fair Value Gross Liability	0	0
Derivative Asset Fair Value Net Asset	1,530	0
Derivative Liability Fair Value Gross Liability	0	2,578
Derivative Liability Fair Value Net Liability	0	2,578
Derivative Liability, Fair Value, Gross Asset	0	0
Not Designated as Hedging Instrument [Member] \| Commodity price swaps
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	2,168	7,713
Derivative Asset Fair Value Gross Liability	0	0
Derivative Asset Fair Value Net Asset	2,168	7,713
Derivative Liability Fair Value Gross Liability	76	0
Derivative Liability Fair Value Net Liability	76	0
Derivative Liability, Fair Value, Gross Asset	0	0
Not Designated as Hedging Instrument [Member] \| Commodity price swaps
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		4,133
Derivative Asset Fair Value Gross Liability		0
Derivative Asset Fair Value Net Asset		4,133
Derivative Liability Fair Value Gross Liability		3,685
Derivative Liability Fair Value Net Liability		3,685
Derivative Liability, Fair Value, Gross Asset		0
Not Designated as Hedging Instrument [Member] \| Foreign currency forward contracts
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Asset Fair Value Gross Liability	0	0
Derivative Asset Fair Value Net Asset	0	0
Derivative Liability Fair Value Gross Liability	5,397	6,722
Derivative Liability Fair Value Net Liability	3,589	6,722
Derivative Liability, Fair Value, Gross Asset	$ (1,808)	$ 0

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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