Derivative Instruments And Hedging Activities (Summary Of Balance Sheet Locations And Related Fair Values Of Outstanding Derivative Instruments) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Mar. 31, 2020
Derivative [Line Items]
Derivative Asset Fair Value Net Asset	$ 17,588	$ 37,644
Derivative Liability Fair Value Net Liability	14,215	15,766
Accrued Liabilities [Member]
Derivative [Line Items]
Derivative Liability Fair Value Net Liability	12,985	15,069
Prepayments And Other [Member]
Derivative [Line Items]
Derivative Asset Fair Value Net Asset	17,588	37,644
Other Noncurrent Liabilities [Member]
Derivative [Line Items]
Derivative Liability Fair Value Net Liability	1,230	697
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7,526	0
Derivative Asset Fair Value Gross Liability	(1,784)	0
Derivative Asset Fair Value Net Asset	5,742	0
Derivative Liability Fair Value Gross Liability	1,230	8,812
Derivative Liability Fair Value Gross Asset	0	0
Derivative Liability Fair Value Net Liability	1,230	8,812
Designated as Hedging Instrument [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7,526	0
Derivative Asset Fair Value Gross Liability	(1,784)	0
Derivative Asset Fair Value Net Asset	5,742	0
Derivative Liability Fair Value Gross Liability	1,230	8,812
Derivative Liability Fair Value Gross Asset	0	0
Derivative Liability Fair Value Net Liability	1,230	8,812
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	11,846	37,644
Derivative Asset Fair Value Gross Liability	0	0
Derivative Asset Fair Value Net Asset	11,846	37,644
Derivative Liability Fair Value Gross Liability	12,985	6,954
Derivative Instruments Not Designated as Hedging Instruments, Loss	0
Derivative Liability Fair Value Gross Asset	0	0
Derivative Liability Fair Value Net Liability	12,985	6,954
Not Designated as Hedging Instrument [Member] \| Nymex Futures Contracts [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	7,412
Derivative Asset Fair Value Gross Liability	0	0
Derivative Asset Fair Value Net Asset	0	7,412
Derivative Liability Fair Value Gross Liability	2,578	0
Derivative Liability Fair Value Gross Asset		0
Derivative Liability Fair Value Net Liability	2,578	0
Not Designated as Hedging Instrument [Member] \| NYMEX WTI Short [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7,713	0
Derivative Asset Fair Value Gross Liability	0	0
Derivative Asset Fair Value Net Asset	7,713	0
Derivative Liability Fair Value Gross Liability	0	3,197
Derivative Liability Fair Value Gross Asset		0
Derivative Liability Fair Value Net Liability	0	3,197
Not Designated as Hedging Instrument [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	4,133	4,564
Derivative Asset Fair Value Gross Liability	0	0
Derivative Asset Fair Value Net Asset	4,133	4,564
Derivative Liability Fair Value Gross Liability	3,685	3,757
Derivative Liability Fair Value Gross Asset	0	0
Derivative Liability Fair Value Net Liability	3,685	3,757
Not Designated as Hedging Instrument [Member] \| Foreign Exchange Forward [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	25,668
Derivative Asset Fair Value Gross Liability		0
Derivative Asset Fair Value Net Asset	0	25,668
Derivative Liability Fair Value Gross Liability	6,722	0
Derivative Liability Fair Value Gross Asset		0
Derivative Liability Fair Value Net Liability	$ 6,722	$ 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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Aggregate fair value of all derivative assets designated as hedging instruments. Includes instruments designated as cash flow hedges, fair value hedges, and hedges of net investments in foreign operations.

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Amount of realized and unrealized loss of derivative instruments not designated or qualifying as hedging instruments.

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