Financial Instruments and Risk Management (Fair Value of Derivative Instruments Not Designated as Hedging Instruments) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Commodity derivative contracts \| Obligations
Derivatives, Fair Value [Line Items]
Derivative liability	$ (41,645)	$ (12,833)
Commodity derivative contracts \| Accounts receivable
Derivatives, Fair Value [Line Items]
Derivative asset	0	13,050
Commodity derivative contracts \| Accounts payable
Derivatives, Fair Value [Line Items]
Derivative liability	(312,448)	(89,842)
Commodity collars \| Accounts receivable
Derivatives, Fair Value [Line Items]
Derivative asset	0	0
Commodity collars \| Accounts payable
Derivatives, Fair Value [Line Items]
Derivative liability	$ (15,929)	$ 0

Fair value, before effects of master netting arrangements, of a financial liability or 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. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Period Type:	instant